I will say this. When I started working in the clinical lab, it took about a full ml of serum or plasma to run an electrolyte panel, sodium, pottasium, choride and bicarb. It took two instuments to do so.
When I left ten years later we could do Chem 20's on one instrument with about a half an ml.
Right. Chem labs require far less sample than do biological tests, looking for analytes such as antibodies or antigens. My part of the lab performs antigen/antibody type tests. The other part of the lab performs molecular tests, such as PCR. The smallest sample size I ever used was 5 microliters and that was sampling by hand, using a micropipette. Most of our platforms/tests required at least 50 microliters PLUS dead volume and increasingly, platforms were automated, rather than manual, meaning the dead volume was absolutely necessary. The thermocycler (to run PCR tests) that I sometimes prepped samples for used 600-800 microliters per test. Now, that's been about 3 years since I've done that work. Specifically, the PCR test was looking for replicating virus.
There are microarrays that can be used to determine gene expression. A much smaller sample size is required.