OK, when I give blood, they take a blood drop and put it in the blue solution; if it drops pretty quickly my levels are OK. If it’s borderline, they put the blood in a machine, and you get results of, say, 12.6, 14.2, 15.6, and acceptable is in the 13.5 - 16 range. What do those numbers mean? Looking online about hematocrit, they’re getting figures like 38%, which makes sense as it’s measuring red blood cells by volume–right? But what are the numbers they’re using in my measurements and how do they compare to the other measurements?
Also, anecdotally, it seems I’m always going to have an OK hematocrit if I have a huge meal right before going to donate, while a smaller meal will get me deferred. Does this make sense or am I seeing connections that aren’t there?
The numbers you’re referring to is the hematocrit expressed in grams of hemoglobin per deciliter of blood volume (g/dl), rather than a percentage. IIRC, you can convert the g/dl figure into a percentage by multiplying by 3, so that a hemotocrit of 13 would be about 39%.
Hematocrit is basicly measuring the solid part of the blood.
A small amount is pulled in to one two or three capilary tubes. These are then evenly spaced in a centrafuge and spun for a short time. When they come out, they are compared to a standard. The tube will have a straw colored fluid at the top, then a very thin white layer then the red layer. The ratio of solid to liquid tells us the number and/or size of red blood cells in the whole blood.
(these are sea level values, they are higher at altitude)
Are you sure you aren’t confusing hematocrit with hemoglobin?
The values you’re using are more within the normals for hemoglobin which is the oxygen carrying protein in the blood.
It’s more liekly to be the haemoglobin based on the values you gave.
If it’s too high it can cause problems for people not used to that amount (say someone with chronic anaemia) and it can also mean that the blood is “thicker” or “stickier” than normal. Fine if it’s your blood and you’re used to it, not if you’re not.
If it’s too low then
a) you, the donor will be made anaemic by the donation, which is something to be avoided.
b) the amount of blood they take from you won’t be ideal for donation because the red blood cells (the part used for transfusion) won’t be in optimal condition for carrying oxygen.
If you have chronic anaemia you can walk around quite happily (until you have a major illness or accident) with a haemoglobin of 7, but if you drop from 13 to 10 in a day you’ll know all about it.