What is the yellowish fluid that escapes after a blood clot?

The yellowish fluid that escapes after a blood clot is called serum. Serum is the liquid component of blood that remains after the red blood cells, white blood cells, and platelets have been removed. It is mostly water, but also contains salts, proteins, hormones, and other substances.

When a blood clot forms, it traps the serum within it. As the clot dissolves, the serum is released. This can cause swelling and bruising in the area around the clot.