Not a domain expert, but as I recall most of the things they want to test for aren't present at a sufficient level in the blood stream to get a statistically si

Not a domain expert, but as I recall most of the things they want to test for aren't present at a sufficient level in the blood stream to get a statistically significant sample from a few drops. Blood sugar is a relatively high percentage of your blood stream, which is why strip-based glucose monitors work.