Fibrin fibers in clots formed in the presence of elevated prothrombin levels are thinner and more densely packed than fibers from normal prothrombin levels.

Transmission electron micrograph of fibrin gel network from clots formed in the presence of 100% (A) and 300% (B) plasma prothrombin levels. Fibrin fibers were thicker and less dense in the presence of 100% prothrombin (A) and thinner and more densely packed in the presence of 300% prothrombin (B). Clots were formed in microtiter wells and fixed as described in “Materials and methods.” The fibrinogen concentration was 2 mg/mL. Original magnification × 10 000; bar 0.5 μm.