Why do you need to take many small samples when taking a bloodtest? Why can’t they just take one and use small amounts from there?
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Each tube’s additives prepare the blood for the testing. If you’re counting blood cells you need the blood not to clot (so the blood is still liquid and cells are discernable) so you use an anticoagulant tube. If you want to test for serum electrolyte levels, you use a tube that, when spun in a centrifuge, will separate the liquid portion of the blood from the solid (and clotting is ok, even preferable). If you want to test for certain types of metabolic activity you sometimes use a tube whose additives kill all the cells inside, essentially “freezing” the metabolism of the blood which continues as long as those cells are alive. This maintains the levels of the chemicals you’re trying to measure. Each color tube has specific additives (or none) that make testing possible.
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