What color is blood?

I’ve always heard that blood is blue and only turns red when introduced to oxygen. My girlfriend (a medical student) says that this isn’t true, although she doesn’t know why veins are blue. Any feedback?

If blood is red, why do your veins look blue?

Blood can have a wonderful array of colors ranging from bright red to nearly black with deep red highlights. But the colors are all on the red side of the spectrum and never blue.

I work on dead people. I release pools of blood. It’s mostly a dark red, which appears standard Crayola red when you let a long thin drip of it smear out across a plastic gurney. As a pool of it gets deeper, it looks darker red. If you release a whole lot of it at once, it looks almost black, but where light reflects off it, it has a color like red wine in a deep goblet. A pleural cavity full of blood clots will be almost purple-black. But never blue.

The only time dead people’s blood is bright red is if they’ve died of carbon monoxide poisoning. CO affects hemoglobin the same way oxygen does, except with 200 times greater affinity - that is, it doesn’t leave.

Because hemoglobin is such a wonderful little piece of lace, with that iron molecule at the center, the wavelengths of emitted light can change a lot if the iron binds oxygen.

When I used to work on live people during my surgical residency, the difference in color between blood from arteries (bright red) and blood from veins (dark red) was very evident to the eye. Helped you to know at a glance if that trauma patient was bleeding arterial or venous blood. Or if you’d got the needle in the wrong femoral vessel…

But it was never blue.

One of the great and popular misconceptions is about the color of blood. I’ve had students (future science teachers) tell me that their doctors (!) told them that blood is blue until it hits the air! If you’ve ever donated blood, you’ve seen what color venous blood is when it’s collected in those transluscent bags. It’s dark red. And if you’ve ever had a deep cut, you’ve seen the color of oxygenated blood. It’s pretty bright red. One source of the misconception (and many others) is student text books. In this case, the attempt to make the distinction between oxygenated and deoxygenated blood is often illustrated by the picture of the man with red arteries and blue veins. Ergo, we have two different colors of blood, red and blue. But, in truth, our blood is mostly dark red or brighter red. You’ve seen it, but you haven’t put your observations up against what you’ve heard. Mark Twain said, “I never let my schooling interfere with my education.” You should do the same. Pay attention, grasshopper.

Cats given acetaminophen develop methemaglobinemia which gives their blood a chocolate color.

Yes, well it’s easy for you to say that! :smiley:

Good link, KarlGauss.

Good report, Hawk.

I’m sorry, and this may be total heresy, but I gotta call *partial * bullshit on a Cecil column, and although it’s not written by the Man, it was sanctioned by him. If that explanation were correct, and it is partially correct, because the phenomenon he reports on is, in fact, observable, what accounts for the fact that an animal blood vessel, mammal or bird, is blue when we dissect it? Clean a chicken breast before cooking it. Don’t you see BLUE veins? A steak? BLUE veins. No blood in them. No light penetrating skin. What’s the explanation? I’d suggest that the tissue has its own coloration. Veins are blue. That’s the preferred explanation. It’s confusing to trot out mumbo jumbo about light absorbing, diffusing, etc. etc. While that may be part of the explanation (and I’m not convinced it’s a significant part of the answer), a perfectly good enough part of the answer is the reason that veins look blue is that…they’re blue.

And understandably so. I don’t know about the rest of you but my veins look blue. That doesn’t mean the blood in them is blue and when my blood is taken it is a real dark red.

How are you determining that the vessels you see are veins and not arteries? Unless you can follow the vessel to its origin, or have histology to tell you that the vessel is, in fact, a vein, than your statement is meaningless. Also, your statement, “no blood in them” is not correct. Unless the chicken or cow had a major vessel cannulated and a flushing solution pumped through, there most definately is blood within the vessels you are observing. An empty artery /vein/arteriole/venule/ looks like a lymphatic vessel; clear, colorless, and difficult to localize unless you know what you are looking for.

You’re absolutely correct. I don’t know what types of vessels I’m seeing in the bird. They may be arteries or veins. I’m just suggesting that blood vessels may have their own coloration and that may be a good part of the explanation for why they look blue. Obviously, the vessels near the surface on our arms are veins. The ones deep in a chicken breast are most probably arteries, in fact. Direct observation of them shows no blood in them, however. The tissues have their own color. In my experience, some vessels tend to be lighter, some darker. As a vet, you must have a lot of experience with this. Do some vessels have more inherent color than others?

Well, as a surgeon I rarely see vessels that are “empty”. I do sometimes milk the blood out of a bitch’s ovarian artery and vein prior to ligation (so that when I transect the vessel I do not get sprayed). In those vessels, the artery and vein are indistinguishable from the surrounding supportive tissue (mesovarium) which is fairly clear itself.

It might be useful to remind those who don’t read your nickname that you’re a veterinary surgeon. :smiley:

When I was in college, one of my roommates hanged himself. I was the one who found the body. What I remember was that his entire body (he was naked) was white, with a lot of dark blue blood vessels. At least that’s the image that stayed in my mind all these years; admittedly I was too traumatized to perceive (and remember) everything accurately.

Did you get a 4.0 that semester?

BTW, why do they collect blood from veins rather than arteries?

The reason I ask is, yesterday I took my elderly mother for her physical. The doctor wanted various blood tests so the next stop was the lab.

First phlebotomist: a very young woman, maybe 22. She tapped and tapped – spent a good 15 minutes (by the clock) before deciding to try the only vein she could feel at all, though she said it was a ‘small one.’ She inserts the needle and starts digging around, for nearly a half minute – not so much as a drop. She apologizes, tapes over the wound, and goes off to get a more experience woman.

Second phlebotomist: looked around forty. Very nice, and kind, and gentle with my mom. (She’s got Alzheimers, btw, which is why she needs to be accompanied everywhere.) More tapping, more tapping. She tries for a vein in the other elbow. A tiny trickle, not enough for even the tube they always discard. Tapes that wound, tries right hand. A bit more blood, she actually gets to one of the collection tubes, but it stops flowing too soon to be usable. Tapes right hand, tries left. Even less blood than the first try.

Second phlebotomist apologizes, says they aren’t allowed to try more than three times, can we come back the next day? I tell her no, because each trip requires two of us to get her there, and takes a minimum of three hours from start to end, and we simply can’t take more time off that soon. So she goes away and gets the director of the department.

Third phlebotomist: woman in her fifties, I think. She goes back to the first elbow. Lots of tapping, then she slip the needle in, one smooth stick, and the blood starts flowing. Yay! Happily she managed to get all four tubes filled and taped off the final wound. (Moral: if you need your blood drawn, ask for the oldest person in the department!)
The real point of all this is, some people have rotten veins. They’re small or collapse easily or I don’t know what, but getting blood drawn is pretty much a prolonged torture each and every time.

So – couldn’t they try taking blood from an artery, if the veins are shot? Or how about another part of the body? I’m guessing, but it seems to me that the veins coming up from your legs must be larger (since your legs are bigger than your arms) so why not stick you behind your knee or something?
There just has to be a way to draw blood that doesn’t require subjecting a frail old woman who really doesn’t understand what is happening to almost 40 minutes and being stuck five times. :mad:

Sampling from an artery is usually not a good idea. Post test bleeding, should it occur, can be life-threatening. More likely is the possibility of damaging the artery, or causing a clot to form within it. If that occurs, the parts of the body being fed by the artery could die. This is not an issue when drawing blood from veins.

In terms of taking blood from a vein in the legs, the main concern is causing a clot to form. Should that happen, the clot may enlarge, dislodge, and travel to the lungs. That could be fatal. Interestingly, this complication is very rare when blood is taken from an arm or hand vein.

Another reason is that arteries are typically buried much deeper in the body for obvious reasons - they need to be protected from being nicked, cut, and poked. Consequently, they’re not anywhere as easy to find. Yes, I know you can palpate a number of them, but they’re still not as accessable as veins which are virtually right under the surface in many places, your mom’s experience notwithstanding . Also, arterial walls are much thicker and are harder to puncture. If you think yesterday’s experience was unpleasant, imagine trying to find and then get through a tough artery wall. On second thought, don’t.

Dude, tactful much? :dubious:

Sorry. Was that bad? You know that legend, about how if your roommate dies . . .