What is the color of veinous blood?

General Questions
#1

I can’t believe I’m in the middle of an argument about this, but I am. Apparently, much of the world thinks that veinous blood is blue. The general line of specious reasoning is twofold:

  • Veins are white when empty, but blue when there’s blood in them (mine actually look green to me, except where they’re purple, so I may not, in fact, be human).
  • As soon as blood hits the air, it becomes oxygenated and therefore becomes red. Therefore, you never catch blood being blue, but it’s blue. Trust me.

The Dope has already weighed in on this: http://www.straightdope.com/columns/read/1419/if-blood-is-red-why-do-your-veins-look-blue. Unfortunately, the word of a mere phlebotomist apparently doesn’t cut it. It’s beginning to feel like an argument about the existence of gods.

Can anybody please give me a winning argument? Qadgop, perhaps?

#2

IIRC, Qadgop has repeatedly debunked this in the past. It’s dark red.

#3

Definitely dark red–arterial blood is bright red. (Hellpaso, R.N.)

#4

So why did they teach me the blue-blood theory in science class? :confused:

#5

Could you just immerse something red in milk to show the change?

#6

Because they were misguided.

#7

Good to know, but with five minutes between a search, and not knowing what to search on, I haven’t been able to find anything.

#8

Have you ever gone for a blood test? We use evacuated tubes (i.e. no air) to suck the blood out of your veins and into the tube. The color the blood is in the tube is the color the blood is in your veins. Usually dark red, purplish almost. Sometimes it looks almost black with a reddish-purple accent.

#9

Don’t know what you’d consider proof. You can point to a couple of things to begin with. 1) anyone who has cleaned chicken will know that there are empty blood vessels that are, themselves, colored blueish. Therefore, their blueish appearance is not the result of the color of the fluids within, contrary to the “evidence” that is sometimes put forth that venous blood must be blue because we can see blue blood vessels in the backs of our hands, for example.
2) anyone who has donated blood can see the venous blood filling the bag and it is dark red. Yes, I know the argument: it’s simply turning red the instant that it comes in contact with the oxygen in the air. Of course, those bags are empty to begin with, so that argument is pretty lame on the face of it. But the blood in the tube leading out of your arm and into the bag is also obviously dark red, and there isn’t any air inside that tube as the blood flows through it. So the blood *coming out of you * is obviously dark red.
(The history and persistence of this and other misconceptions is the bane of the science teacher’s existence. Well, it’s ONE bane. Teaching entails multiple banes.)

#10

It is possible to have brown blood…if you have methaemoglobinaemia. Of course, it’s not exactly the best situation to find yourself in…

The blood really is dark brown, the treatment is intravenous methylene blue, and the patient slowly turns from a cyanosed blue, through a lovely shade of green, back to a nice healthy pink. One of my colleagues recently treated a teenage patient with methaemoglobinaemia that had occurred after she DRANK a bottle of amyl nitrate…she hadn’t realised it was meant to be inhaled.

I think the blue blood misperception is because the diagrams commonly use blue and red to make it easier to understand the circulatory system- much in the same way atlases use blue for the sea and green for land, but in that case everyone knows that water isn’t really blue and land isn’t really green.

#11

That’s definitely one source of the misconception. But I recently had an education student tell me that her doctor had told her the same thing, including the bit about blood instantaneously turning red when it hits the air. I wondered where the guy studied medicine, the Grace L. Ferguson Stormdoor Company and Medical School?

#12

Yeah, one of the things I found on google was this, with two MDs posting: http://yarchive.net/med/blood_color.html. The first guy, Harris, has the right answer. The second guy, Fox, believes veinous blood is blue. He makes a few specious arguments, and admits that he’s color blind, but he believes it’s blue. :rolleyes:

I’ve made all the above arguments. So far I’m not getting traction. And the person I’m arguing with is a nurse, for Pete’s sake.

#13

This is the best argument I’ve got. There ain’t nothin’ in those bags, but apparently people believe that, no, there’s enough oxygen in there to oxygenate a whole pint of blood and turn it red.

Another thing that utterly amazes me is that veinous blood is not completely deoxygenated, so even the blue-blooders could claim a win in their cozy universe if they’d go with that line. But no…

Fully deoxygenated blood is not blue either, but I’d drop the whole argument if I just got the person to admit that veinous blood isn’t blue. But, again, no…

#14

Sorry, I didn’t read this short post carefully enough. Yes, that’s got to be the answer. Even if the tube weren’t evacuated, after the blood starts flowing there’s nothing in there but blood.

If I fail to convince my worthy opponent, I’ll suggest that the next time I’m up her way we put on moon suits, take one of her patients into a room filled with the gas of her choice, and cut into one of the patient’s veins.

#15

Does she have proof for the “veins are white when empty” bit? My “veins” are all bluish, even the ones that are really arteries. If arterial blood is red and the blood vessels are white, why are there no red blood vessels showing in my wrist? That’s what I’d expect to see if the blood vessels were white or clearish.

#16

Actually, she’s not advancing the “empty veins are white” argument. I just picked that assertion up in my readings as one of the arguments people use. I personally don’t know what color veins are; I’d imagine it varies. I don’t think it’s material, since that would open up another argument about the optical properties of veins, and I’d need some pretty sophisticated optical equipment, and a cadaver, to conduct it.

#17

Someone has already done it. Here’s a journal article (Applied Optics) on why blood vessels (both arterial and venous) appear blue.

#18

This article explains the misconception, and also provides a picture of arterial vs. venous blood.

#19

On the veterinary side, I’ve drawn blood on thousands of animals by now. I’ve used both evacuated tubes and I’ve drawn it directly into a syringe. Both methods introduce zero oxygen or air to the blood as it exits the vein. Always dark red, unless the patient is under general gas anesthesia, then very bright red.

Your nurse friend is not very bright, has she never drawn blood herself? I’ve heard some crazy stuff come out of RN’s mouths, sometimes I wonder about “nursing school” and what the heck really goes on there!

#20

I was just about to bring that up! I do wonder what blood would look like if it was completely deoxygenated. Considering oxygenated blood is bright red, and low-oxygen blood is a dark red/almost-purple color, the blue-blood theory almost makes sense.

Wiki has an uncited paragraph about deoxyhemoglobin that says:

The first two sentences are Greek to me - can anyone explain?