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0 pointsCptFribble8y ago0 comments

There are a few reasons you collect a full vial instead of a tiny one:

1. Multiple tests. Most people aren't going to the doctor for a single test. A majority of the testing is Comprehensive Metabolic Panels, which covers 20-30 different things at least. Many patients get a CMP plus other stuff, so enough is drawn for all the tests at once.

2. Possible retesting. There are dozens of things that can go wrong between drawing the blood and sending a result to the doctor. Maybe a tech drops the tube and spills some blood out. Maybe the machine has a problem mid-test and you have to rerun the samples after it's fixed. Maybe the patient has a critically high/low range of something and you need to retest for confirmation. The worst possible scenario for a lab is to have to call the patient back in for more blood, because that causes patient pain and could make the doctor start using a different lab if they're perceived as unreliable. There's actually a legal requirement for labs to store blood for a week after testing, just in case.

3. Different test requirements. The CMPs usually test the serum only (i.e. your blood gets put through a centrifuge), but there are a variety of tests that run on whole blood. Because of the possible re-testing above, and because whole blood test samples need to have anticoagulant added, you'll usually have two separate tubes drawn for whole blood vs. serum tests.

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2YwaZHXV8y ago

OK, so these are more business reasons for bigger samples than technical reasons.

1. Ok, so that can still be done with small samples, it's just a matter of collecting enough. The link I gave showed 15 tests in 30ul of sample. So, 60ul would be enough for your 30 tests. The amount used per test (for many many tests) is still very small compared to the amount drawn.

2. I imagine if a tube is dropped and some sample is lost they consider the whole sample lost. Since if sample got out that also means that stuff can get in, possibly contaminating it. The poor customer experience of having to go back in to be re-drawn is a poor business choice, but again, not a technical hurdle with being able to perform tests. Having enough sample for re-testing a week later is also just a matter of collecting sufficient sample. So, you would need 120+ul of sample (from previous example of 30 tests) to meet that requirement (plus some amount for loss in equipment, etc). But, it is still a far cry from the 2000+ul typically drawn.

3. You actually often have more than 2 drawn, since each tube has a different kind (if any) anticoagulant and if they get sent to different labs they may need duplicates of the same anti-coagulant. This also doesn't have anything to do with the size of the sample required for a test. So, you can collect a bunch of small samples instead of bigger samples. That's not a technical hurdle for being able to perform a test on a small volume of blood.