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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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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Because multiple samples mean if there is something in your bloodstream, they have a higher chance of detecting it instead of just one sample.

As blood sits in the tube, more specifically, blood cells sit with serum/plasma, chemical reactions are still occurring. As a result, some chemicals we are testing for may be reduced or increased depending on the specific test. For all tests and instruments there are specific ranges of time which the blood can be used for that specific test before it has been in the tube too long to match the levels in the body.

It depends. Blood deteriorates quite rapidly outside of the body so they need to either do the tests right away or add anti-clotting agents to the blood before sending it to the labratory. However different chemicals may affect the tests so depending on what test is going to be conducted you might have to use different anti-clotting agents. Some of the chemicals added to the blood might also be part of the test and just needs to be added as soon as possible.

There are ways to reduce the amount of needles used when taking multiple tests. You can hook up multiple vials to the same needle either one at a time or all at once. Another way is to first draw blood into a small bag and then use this to fill up the test vials. However the nurse still have to do this initial blood work all at once. So quite often the nurse is sitting in front of the patient handling their blood in order to get it into the correct vials and doing some tests. If you have issues with seeing blood you can tell the nurse about it and they will try to hide it from you.

If you’re concerned about a bloodstream infection, you need to confirm that it’s the blood and not a contaminant. Thus you get multiple peripheral samples.

I used to do IT work in a worldwide lab. In many cases its a second reference sample. In the case of a dire test result they will test with a second machine – in the case of a positive HIV test we would send the second tube to a independent lab for testing. Our system was highly automated and the machines would take a sample from the referenced tube to then further process. A single reference tube might be processed through several machines – each removing the desired amount to start processing.

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.

I work with genetic tests, and we need a miniscule portion of DNA to run our test. But we need to extract that from 10 mL of blood. So most of what was in the tube we receive is waste to start with.