I was having an argument with a friend the other day that I, being two metres tall and of relatively solid build, would contain more blood than she, being about half a metre shorter and of remarkably slight build. She seemed convinced that despite the obvious difference in size we both would contain the same amount of blood.
Personally, I think this makes no sense. I’ve donated blood so I’ve heard the line that an average person contains so-and-so much amount of blood (which I’ve inconveniently forgotten right now) but I always assumed that was a widely average figure.
So, who’s right? Do big people in fact contain more blood?
The idea of blood volume being unrelated to a person’s size is highly counterintuitive. In view of the purpose of blood, how could the same volume adequately serve a 90-lb woman and a 350-lb man?
Googling produces such things as:
"Blood volume is variable, but tends to be about 8% of body weight. Factors such as body size, amount of adipose tissue, and electrolyte concentrations all affect volume. "
“In an average healthy adult, the volume of blood is about one-eleventh of the body weight.”
“The body of an adult male contains about five litres of blood, that of a woman or a child less.”
You’re right. women and children and smaller, slighter men probably have less blood than the textbook amount.
That is why there is a minimum weight limit (I think it’s 7st 12lbs, or about 50kg) to donate blood, small people simply can’t afford to lose that pint!
I was once working on a golden retriever with a severe anemia. The dog was not going to survive without transfussion and the cause of the anemia was fixable, but the owner balked due to the cost of commercially available blood. She said she would bring in her other dog and we could collect from it. We agreed, and she returned in a few minutes with a little yorkie that weighed around 3 pounds.
I’ve always been told the limit is 110 pounds here. I don’t know if that’s a universal thing in the US no matter who’s collecting, but one time I had upcoming surgery and they said I should donate a just-in-case unit for myself.
Seeing as it was special circumstances, they did let me, but they broke out extra-small equipment and I had to come in twice, donating a half pint each time. I weighed about 105 at that point. I’ve never topped 108, so I’ve never been allowed to donate under any other circumstances.
Just finished doing a remote at United Blood Serivces. Their rule of thumb is that the average person has just over a pint of blood for every 25 lb. of body weight. And yes, they have a minimum weight for donors. 110 lbs. sounds about right.
I think it might be 105 lbs… I know that my sister has never weighed more than about 100 and a couple pounds, and she’s never been able to donate blood.
I, however, being seventeen at last, and having been over 105/110 for quite a long time, am going to donate blood with my (other)sister in the fall!
The Red Cross must think that big people have more blood, as every time I go to donate they notice that I’m on the hefty side and ask to take double the normal amount of RBCs with an apheresis machine.
Yes! That’s what happened to me. But I don’t think it has to do with weight. They told me I had a high iron count, so could they collect red blood cells.
With me, they said something to the effect of “We notice you are a big guy. Can we take double the normal amount of RBCs with apheresis?” and only then did they check iron to be sure I could do it.
Well? Don’t keep us hanging, what happened? Did she leave with a yorkie weighing 2 pounds? Did she pay for the commercial blood? Did the retriever go and get his own?
