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Why does blood plasma contain fibrinogen while serum does not?
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blood
Blood sediment in test tubes, showing plasma (clear fluid), red blood cells (red), and the release of hemoglobin into the surrounding plasma (pink).
Blood plasma contains fibrinogen because it is the liquid portion of blood that retains its clotting factors before any coagulation occurs.12
In contrast, serum does not contain fibrinogen because it is defined as the fluid remaining after blood has undergone coagulation. During the clotting process, the enzyme thrombin converts soluble fibrinogen into insoluble fibrin. This fibrin forms a mesh that traps blood cells to create a clot, effectively removing the fibrinogen from the remaining liquid. Consequently, serum is essentially plasma minus the fibrinogen that was consumed to form the clot.3421