Hematocrit measures the percentage of blood volume occupied by red blood cells. Testosterone stimulates erythropoiesis (red blood cell production), which is why TRT consistently raises hematocrit. Elevated hematocrit increases blood viscosity, which can raise blood pressure and theoretically increase risk of blood clots, stroke, and cardiovascular events.
Regular monitoring is essential on TRT. If hematocrit exceeds 54%, most guidelines recommend intervention: dose reduction, therapeutic phlebotomy (blood donation), or more frequent injections.