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  #1  
Old 04-27-2006, 11:38 AM
Dunderman Dunderman is offline
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What can you find out from a blood sample?

If you're a forensic technician or similar with access to a fully equipped laboratory, what can you realistically find out from a blood sample recovered from a crime scene, provided you have no idea who it's from?

Obviously you can find out the blood type, whether the subject is HIV positive and so forth, but what else? Can you establish gender? Age?

Also, how old can the blood sample be before recovering information becomes difficult? How long afterwards can you see things like presence of toxins/alcohol?
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  #2  
Old 04-27-2006, 12:44 PM
Smeghead Smeghead is offline
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Well, speaking from a genetics standpoint, you could theoretically sequence the entire genome. Gender would be extremely simple - just look and see wether there's a Y chromosome or not.
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  #3  
Old 04-27-2006, 01:16 PM
Dunderman Dunderman is offline
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Theoretically, of course you could do that. Could you do it realistically? If so, what time-frame are we talking about?

Just in case she vanity searches: yo, gabriela, get your forensic butt in here!
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  #4  
Old 04-27-2006, 01:32 PM
edwino edwino is offline
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Yes to gender, no to age. I don't know what is done routinely, but it is a possibility that one could identify certain population haplotypes, hemoglobin and cell surface marker isotypes, and other factors and make a reasonable guess at the person's ethnicity, although it would certainly be a probability thing not a definite thing.

One could in theory sequence a genome from a blood sample but it would be highly impractical at present.
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  #5  
Old 04-27-2006, 02:01 PM
Dunderman Dunderman is offline
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Quote:
Originally Posted by edwino
Yes to gender, no to age.
You couldn't even tell the difference between infant blood and octogenarian blood?

Another thing: When testing for the presence of e.g. drugs, you can't actually just test "for drugs", can you? You have to do one test for each drug you want to look for, right?
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  #6  
Old 04-27-2006, 04:20 PM
mks57 mks57 is offline
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Quote:
Originally Posted by Priceguy
Another thing: When testing for the presence of e.g. drugs, you can't actually just test "for drugs", can you? You have to do one test for each drug you want to look for, right?
With a gas chromatograph-mass spectrometer, you can look for anything unusual. As I understand it, most drugs have an identifiable fingerprint.
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  #7  
Old 04-27-2006, 04:21 PM
Dunderman Dunderman is offline
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Is that something an average forensics laboratory would have?
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  #8  
Old 04-27-2006, 05:47 PM
Smeghead Smeghead is offline
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Quote:
Originally Posted by Priceguy
Is that something an average forensics laboratory would have?
Yeah, it's a fairly standard tool. They'd know where to send it even if they didn't have one themselves.
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  #9  
Old 04-27-2006, 06:09 PM
groman groman is offline
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Quote:
Originally Posted by Priceguy
You couldn't even tell the difference between infant blood and octogenarian blood?
I think you would be able to if you wanted to. For one, not that many infants are taking geriatric drugs. I would guess prolonged aspirin use would be visible, as well as cholesterol drugs, etc. Plus there might be a chromosomal test for age, I don't know.
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  #10  
Old 04-27-2006, 07:14 PM
t-bonham@scc.net t-bonham@scc.net is offline
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Quote:
Originally Posted by Smeghead
Yeah, it's a fairly standard tool. They'd know where to send it even if they didn't have one themselves.
Yes, they have it.
But for your average overworked police crime lab, there's a waiting list of 3-6 weeks for this test.

In real life, you won't see results in a few hours like on TV shows.
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  #11  
Old 04-27-2006, 07:18 PM
Sequent Sequent is offline
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I had my blood carbon-dated once. My bith certificate says 1975 but turns out I'm really a mid-80's forgery.
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  #12  
Old 04-27-2006, 07:50 PM
gabriela gabriela is offline
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Did someone ask for my forensic butt?

The cool thing about blood and forensics is 99% of the blood is worthless for DNA analysis. Yes, that's right, folks, red cells are the only common cell in the body that have no DNA, because they have no nucleus. I think about that sometimes when I'm squirting a few precious cc's from a baby autopsy onto the two DNA spot cards we use. It would save blood for tox, and be more useful, if I could just rub liver on the spots. But the people who process them aren't set up to recognize the value of liver. They have this silly idea, if the spots aren't soaked through to the back of the card, they're not quality enough for processing.

In my mind, the red cells in blood serve as a marker for where the technician should look to find the white cells, which have DNA in them.

You don't need a whole genome sequence to look for male versus female. You don't even really need a karyotype. Ever heard of Barr bodies? Anyone with XX has one of the X's inactivated in every cell. It forms a Barr body that is easily distinguished on light microscopy. Rehydrate your stain, or scoop it up on a glass slide if there's lots of it as we so often see, and I can tell you in ten minutes if it's got a Barr body. No one ever asks me, of course. The dead body is usually near by.

But if it's a tiny stain, they won't waste it on rehydration. DNA is the way to go. Right now they are using RFLP's (pronounced rufflups) which are a really kludgy and old fashioned way to go; ask Colibri if you want an explanation. Eventually they will sequence everybody. Right now sequencing takes too long, but they're working on automating it and it'll get faster. Before I retire, everybody's blood will get sequenced, and that way they'll know exactly what genome you have; can match it exactly to your previously set aside blood spot. Or to hairs from your hairbrush. Or cells from your toothbrush. Those being what we ask family for now, when we have to ID an unidentifiable body through DNA. Those results right now take five to ten weeks.

What nobody here has mentioned in re little blood spots at a crime scene is the wonders of blood spatter (never "splatter") analysis. High velocity, medium velocity, low velocity spatter, anyone?

Gabriela
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  #13  
Old 04-27-2006, 07:53 PM
gabriela gabriela is offline
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Oh yeah - forgot to say - red cells useless for age OR gender. First, in a stain, most of the red cells have clotted and/or burst, and are valueless. Second, once you get past the first three days of life, in which you might have a few circulating nucleated erythrocytes, baby RBC = octogenarian RBC. That is because you make all new RBC's all the time; if you are one of the fortunate normals with a properly functioning bone marrow, they have a 120 day life span, after which they are retired by the spleen. Every day, every night, as you sit here reading this, your skull, ribs, breastbone, spine, and hips are oozing out fresh red cells to keep up the supply. So no help in forensics at all.

Except for the spatter patterns. Wow.
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  #14  
Old 04-27-2006, 07:59 PM
gabriela gabriela is offline
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Quote:
Originally Posted by Priceguy
If you're a forensic technician or similar with access to a fully equipped laboratory, what can you realistically find out from a blood sample recovered from a crime scene, provided you have no idea who it's from?

Obviously you can find out the blood type, whether the subject is HIV positive and so forth, but what else? Can you establish gender? Age?

Also, how old can the blood sample be before recovering information becomes difficult? How long afterwards can you see things like presence of toxins/alcohol?
Sorry to hog thread. Wanted to address the OP's questions. You probably cannot find out HIV status from a dry smear; you'd need several CC's for testing. Blood type might need more than a half cc. Gender we said was easy. Age, impossible.

How old can the blood sample be If it has dried, very old. The blood spots the US military is now doing on every member admitted (no more Unknown Soldiers, ever) will keep in a filing cabinet for fifty years. Conceivably longer. We often get forensic information from the cold files on cases 10 or 15 or 20 years old. Preserve it dry, we can work with it.

If it decomposes before it dries, much more difficult. Maybe and maybe not. DNA degrades when bacteria get hold of it.

You need more than a cc to do alcohols and you might need several ccs to do drugs (is that what you mean by "toxins")? If I want cocaine, opiates, fentanyl, amphetamines, alcohol, methanol, and a base and acid neutral screen, I probably need to send the lab 20 cc. So if you're talking about a mere fingerprint's worth of blood smeared on a wall, we can't send that for tox. DNA will be the way to go.

Again, if the blood is decomposed, it'll have alcohol in it made by bacteria, and the value will be meaningless. If it's not, if it got put in a fridge or was in a cabin up North that was cold all winter, it can be tested almost as well the year after it was collected as the day it was collected. Cocaine will go to BE (benzoylecgonine), but that's all.
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  #15  
Old 04-27-2006, 09:04 PM
Vlad/Igor Vlad/Igor is offline
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Addendum: You can get an idea of the ethnicity of the spatter-producer from the 30 or so proteins that are on the outside of a red cell. It is possible to extract DNA from cells other than leukocytes, but it isn't as easy.

RFLP: you make a bazillion copies of a section of DNA, and then cut it up with an enzyme that only cuts at a specific sequence. For instance, the enzyme AvaII cuts only when the DNA base sequence is GACC, and DpnII only cuts when the sequence is GATC. The result is a bunch of cut up DNA strands of several specific lengths that form a distinct pattern when separated on an agarose gel. If you perform RFLP analysis on the right part of a chromosome with the right enzyme, you can tell two or more individuals apart based on their RFPL patterns.

Vlad/Igor, MT(ASCP)
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  #16  
Old 04-27-2006, 09:22 PM
gabriela gabriela is offline
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Thanks, Vlad/Igor.
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  #17  
Old 04-27-2006, 10:00 PM
Smeghead Smeghead is offline
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Quote:
Originally Posted by Vlad/Igor
It is possible to extract DNA from cells other than leukocytes, but it isn't as easy.
I'm not sure what kind of cells you're talking about here, but we extract DNA from tissue samples all the time in our lab. It's actually slightly easier than doing it from blood, because you don't have to lyse the RBCs and pellet the WBCs first. It does take longer, because there's generally more stuff to digest, but it's pretty simple.
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  #18  
Old 04-28-2006, 02:09 AM
Dunderman Dunderman is offline
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Quote:
Originally Posted by gabriela
How old can the blood sample be If it has dried, very old. The blood spots the US military is now doing on every member admitted (no more Unknown Soldiers, ever) will keep in a filing cabinet for fifty years. Conceivably longer. We often get forensic information from the cold files on cases 10 or 15 or 20 years old. Preserve it dry, we can work with it.

If it decomposes before it dries, much more difficult. Maybe and maybe not. DNA degrades when bacteria get hold of it.
The situation is this: I'm writing a role-playing scenario and trying to keep it as realistic as possible. The players find a very bloody kitchen knife and have no idea how old the blood is or whose it is, but it has spent that time in roughly room temperature. Could you find out anything meaningful from such a sample? Gender? Drugs (probably not, due to small quantity)? Approximate time since the stabbing? If they ask you to simply "tell us as much as you can", what could you do?
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  #19  
Old 04-28-2006, 03:40 AM
Smeghead Smeghead is offline
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Quote:
Originally Posted by Priceguy
The situation is this: I'm writing a role-playing scenario and trying to keep it as realistic as possible. The players find a very bloody kitchen knife and have no idea how old the blood is or whose it is, but it has spent that time in roughly room temperature. Could you find out anything meaningful from such a sample? Gender? Drugs (probably not, due to small quantity)? Approximate time since the stabbing? If they ask you to simply "tell us as much as you can", what could you do?
Gender, certainly, if that's what's requested.
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  #20  
Old 04-28-2006, 04:22 AM
gabriela gabriela is offline
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Quote:
Originally Posted by Priceguy
The situation is this: I'm writing a role-playing scenario and trying to keep it as realistic as possible. The players find a very bloody kitchen knife and have no idea how old the blood is or whose it is, but it has spent that time in roughly room temperature. Could you find out anything meaningful from such a sample? Gender? Drugs (probably not, due to small quantity)? Approximate time since the stabbing? If they ask you to simply "tell us as much as you can", what could you do?
First, is there a body? Or a person missing? Because lots of times, knives are used for butchering animals.

Let's assume it's a murder of a human being. The blood will have dried, so it will work just fine for DNA. But let's stop and do the obvious first: fingerprints. Blood is a great medium for preserving the assailant's fingerprints. Very few people wear rubber gloves to a crime. Stabbings are crazy wild moments in which success is not guaranteed, violence takes over without common sense in charge, and in the vast majority of cases, the other person defends themselves before the fatal blow. In situations like that assailants just can't guarantee there will be no prints on the knife. If they do the usual thing, cast the knife away in the moments after they've won, they won't even think about their fingerprints. If they did, they would wipe the knife, which screws your scenario.

Second: DNA. Two kinds. Victim (copious) and assailant (not guaranteed, but quite possible!). Assailants cut themselves more often than you would believe. Vertical shallow cuts along the edge of the palm are classic assailant accidental self-cuts (long cuts across the palm are classic defense cuts). We'd definitely look for assailant DNA. There might be some non-bloody assailant DNA on the handle, too. Wouldn't be much if any, but PCR does wonders.

If your story is in the present day, victim and assailant blood don't do you much good until the police develop suspects. Because there is no central bank of DNA-typed humans to whom to compare it, and because they don't sequence it. So it won't tell you much, although you could do gender. If your story is in the not so far future, it could tell you ethnicity possibly, particularly if your victim or assailant came from one of those little groups that has odd quirks in their blood, but it won't tell you race. It won't tell you height. It won't tell you eye color. It won't tell you age. It won't tell you the way the face looks. So its major use is to match up to the DNA of either a dead body (or living but wounded person), or to the DNA of a guy who swears he was never there, never seen the place, never met her in my life, Officer. And to do that, you have to find the guy first.

If you are working in the slightly farther but not so far off future, everybody born in the USA will have been karyotyped from the umbilical blood, and they'll just stroll down to the databank plug, feed in the sequencing, and ask it to pick out your man. Of course, if he was born in Russia or Mexico or Peru, you might be out of luck.

So the answer so far is: Not much, but scrape that dried blood and hang onto it, and we'll see whose it tells us it is.
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  #21  
Old 04-28-2006, 05:58 AM
Dunderman Dunderman is offline
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Great, thanks for all the info. One last thing: could you tell approximately how old the blood is, ie how long it's been since the murder or whatever it was?
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  #22  
Old 04-28-2006, 06:55 AM
gabriela gabriela is offline
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Quote:
Originally Posted by Priceguy
Great, thanks for all the info. One last thing: could you tell approximately how old the blood is, ie how long it's been since the murder or whatever it was?
Uh, no. Well, only in the vaguest of terms. Wet stain with clots still on it, dry stain with wet clots, red-brown stain, brown stain. Fresh, drying, dry, older. No hard number of days or weeks attached. Once it's old, it stays old. Analogy: any scar on your skin. Say it took a week to go from fresh cut to healing scar with scabs coming off, and six months to mature to old scar. Once it matured to its final form, it stayed that way for years, and no one can tell whether you got it six months ago or sixteen years ago.
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  #23  
Old 04-28-2006, 07:02 AM
Vlad/Igor Vlad/Igor is offline
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Originally Posted by Smeghead
I'm not sure what kind of cells you're talking about here, but we extract DNA from tissue samples all the time in our lab. It's actually slightly easier than doing it from blood...
DNA extraction from the buffy coat of a spun-down EDTA tube, using Qiagen QIamp kit. ~25 mins from draw to quantitation at 260 nm. We have not had good luck with buccal scrapings, and that may be due to a lack of cell deposited on the scraper. We did find a good protocol for extracting DNA from a forensic brain specimen, but I forget the steps at the moment.

Vlad/Igor
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  #24  
Old 04-28-2006, 08:10 AM
Auntbeast Auntbeast is offline
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When I gave birth to my daughter, they gave me a sealed packet of what I assume is blood. It is a metal foil packet placed in a ziploc baggie and written on it is: DNA Card with her sex, name, DOB and a 4 digit number. As well as a happy little note that says: Do Not Open.

It seems nowadays, they give you a sample of your childs DNA from the get-go. I would find it hard to believe that I am raising her and would not have her DNA hanging around the house, but I think it's a nice policy that makes it "easier to find" I suppose. Speaking of which, can you get DNA from poo? What parts of us do NOT give DNA?

Is a drop or two enough blood, or would a diligent parent gather other little bits (hair, nails) to give other information? Or is DNA pretty much the end all be all?
Sorry, I have a 7 month old, poo is my life.

No, this isn't a way to get vlad and gabriela to continue waxing poetic on this interesting subject, why do you ask?
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  #25  
Old 04-28-2006, 11:19 AM
Vlad/Igor Vlad/Igor is offline
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That's interesting; I hadn't heard of getting a blood spot on a newborn hermetically sealed like that. No, you don't want to open it (I know, curiosity is killing you), as you will contaminate the sample with DNA from your sloughed skin cells. I think it might be a bit over the top to give you such a sample, because as you point out, she's leaving a trail of crumbs as it were by licking, drooling, handling toys, getting her hair brushed or being dried off by a towel. ID by DNA can be done from cells left in the environment, and blood relationship determined by comparing nonsense repeats in the DNA. It sounds like the foil packet is some attempt at a chain-of-custody, where her sealed sample is given to you, so that you can later identify it as coming from her.

Ah, yes, stool samples. Wonderful things those. Never open one unless it's under a fume hood. While it is theoretically possible to get human DNA from intestinal cells that hitch a ride with the poop, it would be damn near impossible, as intestinal bacteria outnumber the human cells about a gazillion to one (and make up about a third of stool by weight).

Vlad/Igor
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  #26  
Old 04-28-2006, 01:27 PM
Smeghead Smeghead is offline
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Also, stool tends to be very fatty and just generally difficult to work with. It can be done, but as Vlad said, there will be a lot of bacterial contamination, which may or may not be a problem, depending on what you're going to do with the DNA.

As a slight hijack (much as I hate to distract from the laser-like focus of the thread so far), I read a study about an interesting use of those infant blood spot cards. They were looking at a childhood leukemia associated with a certain chromosomal translocation. They found about a dozen kids that had developed this leukemia, and went back and tested their infant blood. In about two thirds of them, they found the translocation, meaning that they had actually acquired it in the womb, then later on in youth acquired some other insult that lead to active leukemia. I understand there's now work going on to look for periods during gestation that leave fetuses unusually vulnerable to DNA damage. If enough evidence is found, the authors even suggested routine blood testig of all infants to see if they have DNA damage that could lead to cancer, so that they can keep a closer eye on them and catch any cancers earlier.

Anyway, back to poop.
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  #27  
Old 04-29-2006, 05:34 AM
gabriela gabriela is offline
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Quote:
Originally Posted by Vlad/Igor
We have not had good luck with buccal scrapings, and that may be due to a lack of cell deposited on the scraper. We did find a good protocol for extracting DNA from a forensic brain specimen, but I forget the steps at the moment.
Vlad/Igor
Slight hijack:

I'm sorry to hear that about the buccal cells. We retrieve buccal cells for DNA on every homicide victim who has survived to be hospitalized, operated, and extensively transfused. And by extensively I mean massively - three times their own blood volume, for example. We feel the cheek cells are likelier to reflect the victim's own DNA in that situation than their blood.

But I don't know that any officer has yet had to call on the lab to obtain DNA from those cells yet, so I don't know how well they do.

A mitigating factor may be that our patients are dead, and can't feel pain, so we scrape like hell.

We also submit brain, liver, and kidney in varying stages of decomposition from fresh to yuck, and when it reaches yuck, relatively preserved muscle. We have also had to go to DNA from bone in skeletonized unknowns. These have gone to testing and have been successful in making identifications. Don't know if the lab was doing mitochondrial DNA or went for nuclear DNA on deep bone samples.

I hope the forensic protocol works when you do it. I really hope so.
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  #28  
Old 04-29-2006, 05:38 AM
gabriela gabriela is offline
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Quote:
Originally Posted by Smeghead
Also, stool tends to be very fatty and just generally difficult to work with. It can be done, but as Vlad said, there will be a lot of bacterial contamination, which may or may not be a problem, depending on what you're going to do with the DNA.

As a slight hijack (much as I hate to distract from the laser-like focus of the thread so far), I read a study about an interesting use of those infant blood spot cards. They were looking at a childhood leukemia associated with a certain chromosomal translocation. They found about a dozen kids that had developed this leukemia, and went back and tested their infant blood. In about two thirds of them, they found the translocation, meaning that they had actually acquired it in the womb, then later on in youth acquired some other insult that lead to active leukemia. I understand there's now work going on to look for periods during gestation that leave fetuses unusually vulnerable to DNA damage. If enough evidence is found, the authors even suggested routine blood testig of all infants to see if they have DNA damage that could lead to cancer, so that they can keep a closer eye on them and catch any cancers earlier.

Anyway, back to poop.
I knew about the children born with leukemia (commonest outside of Down syndrome is acute myelogenous leukemia, Philadelphia chromosome negative), but I hadn't heard about the periods during gestation that would leave fetuses unusually vulnerable to DNA damage. That's fascinating. I hate to ask "Cite?" when I'm not at all disagreeing with a poster, but can you remember roughly where you learned that? It sounds like something I should be up on... and would be really interested to know.

And, to un-hijack the thread, I totally agree with you and Vlad/Igor about the poop. Seems like most people are not aware their feces are 90% dead bacterial carcases. Until they go on antibiotics.
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  #29  
Old 04-29-2006, 11:34 AM
Caiata Caiata is offline
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Quote:
Originally Posted by gabriela
But if it's a tiny stain, they won't waste it on rehydration. DNA is the way to go. Right now they are using RFLP's (pronounced rufflups) which are a really kludgy and old fashioned way to go ...
Really? I thought STR/PCR was the way of choice, moreso than RFLP, and that SNPs were becoming more frequently used as well! I guess I could be biased given that I'm a forensic chemist & the only time I'm really involved in DNA stuff is when I attend conferences, where everyone talks up the most recent techniques, but I'm certain that here in Australia we use STRs exclusively. I mean ... hell ... you guys don't still use a Southern blot do you? :P

What I understand of blood evidence is such:
  • Probably the first thing the crime scene investigators would do is a presumptive test on the stain on the knife to determine that it may be blood. This test is typically performed using a proprietary device such as the Hemastix, which is a slip of paper with a yellow chemical on the end. You swipe the yellow chemical bit over the stain, then add a drop of water. If the yellow bit turns dark green within a couple seconds, then your stain MIGHT be blood. There are lots of false positives (e.g. rust, tomatoes, etc. - the test works on the basis of chemical oxidation, which the haem part of haemoglobin performs if blood is present, but lots of other things can oxidate the chemical as well) but there really isn't much scope for a false negative on a visible blood stain. Another possibility is the o-toluidine test, which involves 2 steps, and rules out some chemical oxidants, but still has false positives and is a more complicated process - it's not really done much at the scene. Could be done at the lab, though.
  • Determining that the blood is human probably is done by just DNA profiling. However, there are immunoassays such as the Ouchterlony test which also do this.
  • Blood type is really easy, but not very helpful. However, there's a lot of different antibodies being used for blood typing now so it's not AS useless as it used to be. Combining things like A/B/O, Rh, and MN can get as specific as 10% of the population having that combination of antibodies. It can also hint at ethnicity in certain instances.
  • If using a PCR-based profiling kit like Profiler Plus etc., you can get 13 to 16 locations on the genes to create a DNA profile. This is through STRs ("short tandem repeats") which are areas outside of our genes (and thus more likely to vary) that have repeating, short units of DNA (e.g. CATTCATTCATT - I think that's the TH01 locus). The number of repeating units in each locus is the distinguishing factor here. This can individualise blood to a 1-in-a-billion type accuracy, but of course it's likely that two identical twins would produce the same DNA profile. This doesn't tell you anything about the person though.
  • Except for sex, because the amelogenin gene is one of the 13 or 16 loci being tested for. The amelogenin gene is 6 base pairs longer on the Y chromosome than on the X chromosome, thereby allowing us to determine sex.
  • If you have a mixed profile (you can tell because you might get 3 or 4 answers for the same locus, when for a single person you should only get 2) and you are armed with some DNA from a relative of one of the two contributors, you can probably work out which profile is from which person.
  • You could do a rough estimation of age, THEORETICALLY speaking, based upon the length of the telosome (the end part of the chromosome), as each time the DNA replicates the telosome is shortened slightly. However, I don't think many crime labs would undertake this kind of complicated analysis. If your roleplaying scenario is in the CSI:NY world, they might!
  • Foetal blood and infant blood may have a different type of haemoglobin (gamma?) but I'm not sure how long that sticks around.
  • SNPs - pronounced "snips" but meaning Single Nucleotide Polymorphisms - find and identify single points in the genome where the DNA polymerase enzyme screwed up and put in the wrong base. Research is still assessing exactly how helpful this is, but in April I saw a very convincing presentation on the use of a smattering of SNPs to assign a racial group to the profile - caucasian vs south-east asian vs south-west asian vs african vs indigenous Australian, for example. The worst result was something like 60% accuracy for one of the racial groups, I think it was caucasian. SNPs may also be used to determine likely hair colour, eye colour, etc. - this is still in the early stages, but it's developed enough that a crime lab with a fairly high-tech laboratory could potentially do this analysis or outsource it if the case was important enough and there was no other avenue for identfying the bloodstain.
  • I don't know if there would be much in the way of mitochondrial DNA (mtDNA) in a dried blood sample, but due to the abundance of mitochondria in normal cells (not present in red blood cells) mtDNA is often the easiest DNA to find in a degraded sample. mtDNA is identified by sequencing a section of the mt genome. mtDNA is maternally inherited so you can identify that a person is descended from a certain maternal heritage - e.g. link a son to his mother/grandmother/mother's sister etc.
  • Depending upon the amount of blood available you could possibly use an extraction method to attempt to isolate foreign drug substances and then identify them by GC/MS. Every forensic lab should have a GC/MS, it's like we wouldn't even exist without them! However - in my opinion - HPLC/MS/MS is a better method for detecting drugs in blood. I don't know that it's more sensitive per se, but it's more flexible and customisable for the specific type of thing you're looking for. Depending upon the size of the sample and the amount of drug that's present, you might not be able to quantify it, but you could still be able to detect and identify it at low levels. Of course you have to screen for metabolites as well.

    As for testing "for drugs", you're right in that you can't just run one test to identify all possible drugs that may be in a person's system. However, there are shorter "screening tests" you can do to determine whether drugs MAY be present. For example, there are colour tests which involve adding a chemical reagent or two to a drop of extract from the blood, and seeing if a colour change occurs. These are presumptive tests only but are very sensitive and rarely exhibit false negatives, especially in a laboratory setting.

    You can divide the entire range of drugs up into a few classes - "acidic", "basic", and "neutral" tends to work well for analytical purposes - and then use a separatory technique (GC/HPLC/TLC) to look for the presence of each of these classes of drugs. If you find any indication that an acidic drug is present, for example, you can then perform another test to perfect your separation and determine which drug it is (usually by a spectroscopic detector, Mass Spectrometry being the most popular, but infrared spectrscopy works well also).

    There are also immunoassay-based detection methods for drugs, but since they're more biological than chemical, I don't know much about them.
  • If we're talking just a knife, then blood spatter evidence wouldn't really help much. It's more useful in looking at a trail of blood droplets on a surface and determining the direction of the attack, the number of attacks made, and the type of weapon used when making the attack; whether a person was sitting or standing or lying down when they were attacked; etc. These can all be determined by simple trigonometric calculations.

Sorry for the length! If this was a more chemical-related question I could have babbled on even more than this. Kinda scary, huh?
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  #30  
Old 04-29-2006, 01:13 PM
gabriela gabriela is offline
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Hey, Caiata, do you work for private industry? Rufflups are cheap. I work for a state government. They hang onto old methods for a long time. Do what's cheapest. We just year before last stopped using Windows 95. We squeeze every penny until it cries.

The telomere thing is a great idea. I've never seen it done, but who knows when the real world will catch up? One question: how close to age does it get you? You know forensic anthro tends to get you very close to age from birth to 13, within three years from 13 to 20, then by decades from 20 to 50, then "old" and "real old" from 50 on up. Do telomere lengths pinpoint your unknown's age within a year, five years, a decade, or only narrow it down to first or final third of life?

Fetal hemoglobin is gone within three days of birth except in very rare circumstances (some of the thalassemia variants) which I'm sure you know about, but which aren't helpful to the OP.

Yeah, I can't offer up much about blood spatter to a role-playing game scenario that only wants to start with a bloody knife. But if he had wanted to start with a bloody scene!!!

And I'm still waiting to hear if there's a body. What use is a blood-stained knife without a body?
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  #31  
Old 04-29-2006, 01:54 PM
Smeghead Smeghead is offline
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Quote:
Originally Posted by gabriela
I knew about the children born with leukemia (commonest outside of Down syndrome is acute myelogenous leukemia, Philadelphia chromosome negative), but I hadn't heard about the periods during gestation that would leave fetuses unusually vulnerable to DNA damage. That's fascinating. I hate to ask "Cite?" when I'm not at all disagreeing with a poster, but can you remember roughly where you learned that? It sounds like something I should be up on... and would be really interested to know.
All I can tell you is that I was researching a presentation I gave on the AML-ETO (8;21) translocation. It was in the one paper I ran across that was about fetal acquisition, and they just sort of casually mentioned that there was a theory out there about the possible existence of these periods. There was probably a footnote, but I didn't follow it up.

Quote:
I mean ... hell ... you guys don't still use a Southern blot do you? :P
I'm in a clinical lab, not a forensic one, but we still use Southerns for a couple of things. And the technology hasn't changed at all - we still do it in Tupperware tubs, and we have a paper cutter to cut up the paper towels to put on top.

Quote:
We just year before last stopped using Windows 95.
We're currently in the process of upgrading our computer system from our old one. Which is DOS-based. From 1984.
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  #32  
Old 04-29-2006, 04:16 PM
Eleusis Eleusis is offline
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Originally Posted by gabriela
If you are working in the slightly farther but not so far off future, everybody born in the USA will have been karyotyped from the umbilical blood
Is this a sure thing absolutely going to happen, or just possible?

It seems that privacy advocates would fight this tooth and nail.
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  #33  
Old 04-29-2006, 04:49 PM
WhyNot WhyNot is offline
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Quote:
Originally Posted by gabriela
<snip>

Fetal hemoglobin is gone within three days of birth except in very rare circumstances (some of the thalassemia variants) which I'm sure you know about, but which aren't helpful to the OP.
<snip>
Out of curiosity, do preemies maintain their fetal hemoglobin until term, or does it change after 3 days? If a baby needs a blood transfusion before they're 3 days old, do they have to recieve infant blood with fetal hemoglobin, or can they use any old blood (type matched, of course) with "regular" hemoglobin?
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  #34  
Old 04-29-2006, 07:25 PM
Caiata Caiata is offline
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Quote:
Originally Posted by gabriela
Hey, Caiata, do you work for private industry? Rufflups are cheap. I work for a state government. They hang onto old methods for a long time. Do what's cheapest. We just year before last stopped using Windows 95. We squeeze every penny until it cries.
I currently work for a government-run teaching facility, and let me tell you we certainly aren't well-funded in the chemistry department (we don't even have a GCMS, just a GC, what good is that?!?). However, I think there's been a glut of funding here in Australia for DNA-based technology, because even our pathetic teaching lab has an autosequencer and several PCR machines. Our students, who have completed 4 units of Forensic Molecular Biology type courses, graduate without ever having run a Southern blot.

As for computers though, I know the Australian Federal Police still has some equipment that runs off a machine that actually has a TURBO button. You press it, and it switches the CPU from 20MHz to 66MHz. Wow, huh?

Quote:
Originally Posted by gabriela
The telomere thing is a great idea. I've never seen it done, but who knows when the real world will catch up? One question: how close to age does it get you? You know forensic anthro tends to get you very close to age from birth to 13, within three years from 13 to 20, then by decades from 20 to 50, then "old" and "real old" from 50 on up. Do telomere lengths pinpoint your unknown's age within a year, five years, a decade, or only narrow it down to first or final third of life?
I'm not sure how far the research has advanced into this one - I imagine at this stage you can only get to the decade level, as you have to sort of guess how many times a cell would replicate over the course of a person's life. Maybe real biologists know that, but I'm just a pseudo-biologist so I'm not sure However I think there's room there for a really interesting addition to the forensic portfolio of DNA testing - if someone can get the statistics research done.
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  #35  
Old 04-30-2006, 02:38 AM
Dunderman Dunderman is offline
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Originally Posted by gabriela
Yeah, I can't offer up much about blood spatter to a role-playing game scenario that only wants to start with a bloody knife. But if he had wanted to start with a bloody scene!!!
Hey, if a bloody scene ever comes up, you'll be the first one I ask.
Quote:
And I'm still waiting to hear if there's a body. What use is a blood-stained knife without a body?
Well, that's kind of what I wanted to know. There is a body, of course, but I haven't quite decided where it is yet, and at any rate the players find the knife long before they find the body, if they ever do.
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  #36  
Old 04-30-2006, 06:06 AM
gabriela gabriela is offline
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Originally Posted by Smeghead
We're currently in the process of upgrading our computer system from our old one. Which is DOS-based. From 1984.
Smeghead wins.
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  #37  
Old 04-30-2006, 06:13 AM
gabriela gabriela is offline
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Originally Posted by Eleusis
Is this a sure thing absolutely going to happen, or just possible?

It seems that privacy advocates would fight this tooth and nail.
Just possible. Just possible. However, it's likelier to sneak in because there are pressing health reasons for making sure a sample is saved. Not only childhood leukemia and other blood dyscrasias to check for in the infant, but matching cord blood with its wealth of stem cells, to other children (and adults) who need urgent treatment for cancer. Also, my state (and many others) does a dried blood spot card on every infant to check for mitochondrial disorders (MCAD testing). They toss those cards out right now at six months if the tests come back normal, because they have so many of them. All it takes is a policy change to keep them forever.

Also, people tend to OK stuff happening for medical reasons to very tiny babies. You saw that Auntbeast got a dried sample with hers? Hear any outcry?

For that matter, hear any outcry at the national blood spot card filing program of the military? Even hear before that it existed? Ever hear of No More Unknown Soldiers?

I know it's a step (and an opportunity for privacy advocates) from blood spot card filing to karyotyping, but as the technology gets quicker and cheaper, the step gets shorter and faster.

I'm willing to predict there will be national blood spot card filing in the next twenty years, and karyotyping before I retire. Ten dollars on that to any Doper who wants to take me up on it.
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  #38  
Old 04-30-2006, 06:18 AM
gabriela gabriela is offline
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Originally Posted by WhyNot
Out of curiosity, do preemies maintain their fetal hemoglobin until term, or does it change after 3 days? If a baby needs a blood transfusion before they're 3 days old, do they have to recieve infant blood with fetal hemoglobin, or can they use any old blood (type matched, of course) with "regular" hemoglobin?
The proportion of fetal hemoglobin to regular hemoglobin declines very rapidly. Like anything in the body, it's not an all-or-none switch. Red cells filled with mostly mature hemoglobin start appearing rapidly and take over.

Children who need transfusions in the womb (erythroblastosis fetalis, fetal-maternal blood loss victims) are transfused with regular banked blood. Where are we gonna get fetal blood, vampire it off some other fetus through the pregnant woman's belly? I don't think so.

Fetal hemoglobin is different only because it hangs on to oxygen a little longer and gives it up in oxygen-poorer environments than regular hemoglobin. Which figures, if you think about the womb setup.
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  #39  
Old 04-30-2006, 06:19 AM
gabriela gabriela is offline
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Quote:
Originally Posted by Caiata
As for computers though, I know the Australian Federal Police still has some equipment that runs off a machine that actually has a TURBO button. You press it, and it switches the CPU from 20MHz to 66MHz. Wow, huh?
OK, the Australian Federal Police win. Smeghead, take note.
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  #40  
Old 04-30-2006, 06:20 AM
gabriela gabriela is offline
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Originally Posted by Priceguy
Hey, if a bloody scene ever comes up, you'll be the first one I ask.

Well, that's kind of what I wanted to know. There is a body, of course, but I haven't quite decided where it is yet, and at any rate the players find the knife long before they find the body, if they ever do.
If the bloody knife is found in the same room where the killing was done, there'll be spatter.

If not, hack away!

You do ask the weirdest questions. I am so grateful they give me an opportunity to pontificate. I wonder sometimes about the RPG you're writing, what it's like. I bet you're having fun.

I bet the people who play the RPG will be having fun soon, too.
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  #41  
Old 04-30-2006, 04:40 PM
Dunderman Dunderman is offline
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Originally Posted by gabriela
You do ask the weirdest questions. I am so grateful they give me an opportunity to pontificate. I wonder sometimes about the RPG you're writing, what it's like. I bet you're having fun.
I am, but I think you're getting me mixed up with someone else. I only remember asking one role-playing-scenario-related question before, and that was to do with the narrative and happened before you joined.
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