What is that stuff in the bottom of a vial when blood work drawn?

The stuff in the bottom of a vial when blood work is drawn is typically a gel separator or an anticoagulant.

- Gel separator: This is a gel-like substance that is used to separate the red blood cells from the serum or plasma in the blood sample. After the blood is drawn, the vial is centrifuged, which causes the red blood cells to settle at the bottom of the vial and the serum or plasma to rise to the top. The gel separator helps to keep the two layers of blood separate, making it easier to collect the serum or plasma for testing.

- Anticoagulant: This is a substance that is used to prevent the blood from clotting. There are different types of anticoagulants, but the most common one is ethylenediaminetetraacetic acid (EDTA). EDTA binds to calcium ions in the blood, which are necessary for clotting to occur. By binding to the calcium ions, EDTA prevents the blood from clotting.