I am a student and I have a question about blood testing.
Why do Phlebotomists draw blood from vein? For doing blood tests, do we need to extract specific kind of blood extracted/drawn from veins? Or is it possible to extract the blood that is accumulated under the skin and send it to the lab for blood test? So for example, hypothetically, if there is a cut on one person’s arm and he is bleeding, can we just take that blood and send it to the lab for the blood tests?