OK, I know that there are certain types of blood; A, B, AB, & O (along with a positive/negative designation). My question is, what makes one’s blood type whatever it is? Is it the presence/absence of a certain chemical (enzyme, DNA sequence, etc.). Is it concentration of red/white blood cells per mililiter? Or is it something I’m overlooking entirely?
It’s the presence (or in the case of Type O, absence) of antigens, which are proteins on the surface of the red blood cells for identification by the immune system (er… I think that’s what they’re for… can anyone help with what they’re for?). The A and B describe the presence of a certain type of protein. Having both is AB, and having neither is O.
It’s the presence or absence of certain sugars on the surface of your red blood cells. If you have the A gene, you make one type of sugar on the outer membrane of the cells and you are type A. If you have the B gene, you make the B sugar and are type B. If you have both genes, both sugars are expressed and you’re AB. If you have neither, you’re type O.
Smeghead, besides having a cool name, is basially correct about the sugars. Actually it’s different chains of sugars (I think the chains differ from each other by one or two sugars total; I’m not going to look it up. Voet and Voet or Stryer ahould have it. Check a university library.)
However, he fails to note that A-type blood carries an antibody against B-type blood, and vice versa. AB has none of these antibodies, and type O has both antibodies. This is why people with AB can receive anyone’s blood (not counting other factors like Rh) and O can donate to anyone (not counting Rh), but neither donation is a great thing. Only with type-specific blood do you not get any problems, because of those damned antibodies.
(Actually, donating any blood to an AB would probably cause the least problems.)
LL
Sugars, eh? That would explain why my ex girlfriend’s blood (A or B negative, I forget which) was always sweeter than mine (O neg).
::High fives wevets:: Nice simulpost!
Lazarus - thanks. You, of course, are also correct. In that my name is indeed cool. Oh, and the other stuff, too. 
If we want to get really anally specific here, everybody, including O-types, have this antigen: N-acetylgalactosamine - galactose - N-acetylglucosamine - galactose - fucose.
The enzyme coded for by the A gene adds another N-acetylgalactosamine to the second galactose, and the enzyme coded for by the B gene adds another galactose to the second galactose.
And, the antibodies Lazarus mentioned are present not because we’re routinely exposed to other blood types, but because many bacteria and animal cells express antigen types that are close enough so that the antibodies can cross-react.
There. That should do it.
No blood type thread would be complete without mention of the minor blood type antigens. Besides Rh factor and ABO typing, there are bunches and bunches of not-so-antigenic red blood cell surface proteins and oligosaccharides (you don’t form antibodies and reactions against them as rapidly). These normally only come into play when one has hundreds of blood transfusions (you start to get sensitized in this case). This happens with a lot of blood dyscrasias, chronic anemias, and sickle cell disease.
Here is the list of all 22 blood groups (for the record), courtesy Stedman’s Medical Dictionary, 26th edition**
ABO (4 antigens)
MNS (37 antigens)
P (1 antigen)
Rh (4 antigens)
Lutheran (18 antigens)
Kell (21 antigens)
Lewis (3 antigens)
Duffy (6 antigens)
Kidd (3 antigens)
Diego (2 antigens)
Yt (2 antigens)
Xg (1 antigen)
Scianna (3 antigens)
Dombrock (5 antigens)
Colton (3 antigens)
Landsteiner-Weiner (3 antigens)
Chido/Rogers (9 antigens)
Hh (1 antigen)
Kx (1 antigen)
Gerbich (7 antigens)
Cromer (10 antigens)
Knops (5 antigens)
There are also a bunch of other assorted antigens that can cause relatively rare disorders besides these ones.
::bows deeply to Smeghead’s superior knowledge::
Thanks, Smeghead, you’re right, the antigens are sugars, not proteins.
Hmmm… must find a way to distract people from my error…
Hey! Look over there! It’s Ace Rimmer! Wot a guy!
:: runs off ::
So what does the pos/neg mean?
I’m O+. Does that mean I’m a very up and happy person with O blood?
And do animals also have blood types?
I thought there was either a column, mailbag, or SDMB thread on this topic that was very informative. I can’t find it, though.
Yes is the answer. But they of course have different sugar chains, with different letters.
IIRC, horses have 4, giving them a possible total of 16 blood type combinations. Their O type is so rare that it’s usually not counted and the total number is usually stated as 15. However, there is a horse in the TX/OK area that is a very rary Type O donor. He’s taken care of very well! Whenever another horse needs an operation that requires blood, they ship the donor horse to the site for a transfusion. He objects minimally to the phlebotomy needle.
The + or - is commonly used to denote the presence or absence of the Rh antigen. We use ABO and Rh as common blood desiginations because these are the most important, but as stated above there are many other important blood antigens. For example you said you were O Rh+ but your blood could be typed further as O rh+ M+ Lu- K+ Kidd- etc… (i’m just making this up, I don’t actually know what your blood antigens are)
Also the other blood antigens used to be used in paternity testing, but now we use DNA.
You wouldn’t believe the number of call I get saying, “Hey blood guy I’m a A pos and my wife is a A pos but our baby is a O neg. Is the baby mine?” The answers is maybe, the O and Rh negative are recessive characteristics.
I wanted to make explicit, in different terms, something already discussed above.
Even in the absence of previous blood transfusions or pregnancies, the following applies:
If you are “O” you will have antibodies against “A” and “B”.
If you are “A” you will have antibodies against “B”.
If you are “B” you will have antibodies against “A”.
If you are “AB” you will not have antibodies against “A” or “B”.
So, in theory an AB person could accept blood from an O, A, B, or AB. Conversely, in theory, an O person could donate to an O, A, B, or AB (so-called universal donor).
With respect to being positive or negative:
The + or - refers to the Rh system of antigens, the D antigen in particular. If you’re - then, unless you’ve been exposed to + blood (via transfusion or across the placenta) you will not have antibodies.
So, in theory, and I think on the battlefield in fact, an A- person could get A+ blood safely. The next time it would be dangerous.
Well if an O person can give blood to anyone, then how come on ER (the one true source for all medical knowledge) they always “hang another unit of O-”? What about us O+ people? Our’s isn’t good enough to give to just anyone?
By using O neg and not O pos they do two things:
-
They avoid “sensitizing” the recipient to the ‘positve’ antigen and thus prevent future problems for him/her
-
They anticpate the possibility that the recipient has already developed antibodies to the postive antigen
IIRC, somewhere around 35-40 percent (including myself) of the US population is O+; that should make that type very desirable for donation.
To that effect, I remember the Atlanta area Red Cross having special drives to bring in O+ donors – I even have a t-shirt from one of them somewhere in the black hole that is my closet.
They always want more O people giving blood, positive or negative, because it’s the universal donor. Ideally, they like to match the type completely, but in an ER situation, you probably don’t know the patient’s type, and might not have the time to find out, so it’s safest to give them O (preferably O negative). Furthermore, if the patient is O, then the donor absolutely must be O, so even with perfect matching, you need at least the same proportion of O donors as O recipients.
I’m O-, which is only 8% of the US population. You oughta see the technicians eyes light up when I state that I’m O-.
The blood center I donate to (Inova Hospitals, not Red Cross) also does platelettes (sp?). When I asked about donating platelettes instead (you can do it more often), they said my blood is more valuable whole.
And what gives me a warm fuzzy feeling: Inova reserves whole O- blood for babies.
[begins the game of one-upmanship]
I am A+ but aparently more important CMV-. I am a very regular donor and one time they called me pretty late at night and asked me to come in and give the next day (a day or so ahead of my 56 day window BTW). They scheduled an exact time for me to donate and after my donation was complete they put my pint in a cooler and immediately drove it straight to the local children’s hospital where they used it on some child who aparently desparately needed it. They even gave me a special t-shirt.
Yeah, we had my dog tested to see if he could be a donor in our local community, but he had the wrong type. Not sure the same is true for cats. Beyond that, I dunno.
Kind of on a related subject, can I donate if I am taking perscription medication?