What is polycythemia?
Polycythemia is an abnormal increase in red blood cell count that can develop as a side effect of testosterone replacement therapy and necessitates regular blood work monitoring.
Polycythemia refers to a condition where the body produces too many red blood cells, raising hematocrit and hemoglobin levels above normal ranges. While the body naturally regulates red blood cell production, testosterone stimulates erythropoietin, a hormone that signals the bone marrow to make more red blood cells. Men undergoing testosterone replacement therapy may develop polycythemia as a direct result of elevated testosterone levels.
This elevation matters because thicker blood increases viscosity, potentially raising the risk of blood clots, stroke, or heart problems. Polycythemia also can cause symptoms like headaches, dizziness, flushed skin, and joint aches. Not all men on testosterone develop it, but the condition occurs frequently enough that it is considered a recognized side effect requiring attention.
Providers managing testosterone therapy typically order hematocrit and hemoglobin tests at baseline, after 8 to 12 weeks of starting treatment, then periodically thereafter. If levels climb too high, options include reducing the testosterone dose, extending the time between injections, switching delivery methods (such as from injections to gels or patches), or temporarily pausing treatment while blood cell counts normalize. Regular monitoring is the standard approach to catching polycythemia early and preventing complications.