Eli5: What’s the expiration date of blood once outside the body? (e.g. blood taken for tests donations) What about it’s components?
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Depending on the test you are doing, and what you are trying to measure. For example, the measurement of electrolytes, specifically potassium (K+) becomes less reliable over just a few short hours due to most of the K+ being within your cells. And as time goes on and cells start to degrade, this K+ leaks out of the cells into the plasma, and thus giving you a falsely elevated K+ result.
The inverse is true of many proteins measured by different laboratories. Degradation over time. Other components of blood that become raised over time are phosphate and ammonia, and many others.
Another example is the measurement of serum glucose, obviously the body and cells use glucose as energy, so once the sample is out of the body, you want to be analysing that one quite quickly! But there are ways to get around it, and that is using sample tubes that are specially lined with a material that prevents this from occuring.
With haematology, and blood films, the morphology of the cells start to degrade over time, and you can see the misshapen cells, and leaking intracellular components. I ‘think’ some of this is down to the mixing with EDTA in some blood tubes, which is there to stop your blood clotting in the tubes, thus making them difficult to analyse.
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