From the FDA Drug Label
Monitor serum testosterone, prostate specific antigen (PSA), hemoglobin, hematocrit, liver function tests and lipid concentrations periodically (5.1,5.3,5.9,5.13) In addition to PSA levels, the following laboratory values should be monitored while on transdermal testosterone therapy:
- Hemoglobin
- Hematocrit
- Liver function tests
- Lipid concentrations
- Serum testosterone 1
From the Research
In addition to PSA levels, hematocrit should be monitored in a 60-year-old male starting transdermal testosterone therapy. Baseline hematocrit should be measured before initiating treatment, followed by evaluation at 3-6 months after starting therapy, and then annually thereafter. Testosterone therapy commonly increases red blood cell production, which can lead to erythrocytosis (elevated hematocrit) 2. This is a dose-dependent effect that occurs because testosterone stimulates erythropoietin production and directly affects bone marrow. If hematocrit rises above 54%, testosterone therapy should be temporarily discontinued or the dose reduced until levels normalize. Elevated hematocrit increases blood viscosity and potentially raises the risk of thrombotic events, particularly in older men who may have other cardiovascular risk factors.
Some key points to consider when monitoring hematocrit in patients on testosterone therapy include:
- The risk of developing polycythemia secondary to exogenous testosterone has been reported to range from 0.4% to 40% 3
- Different testosterone formulations have varying influences on the development of secondary polycythemia, with intramuscular testosterone cypionate having a higher risk compared to nasal testosterone gel 4
- The prevalence of polycythemia in men treated with transdermal testosterone is lower compared to those treated with intramuscular testosterone enantate, but still requires regular monitoring 5
- Developing polycythemia while on testosterone therapy is an independent risk factor for major adverse cardiovascular events (MACE) and venous thromboembolic events (VTE) in the first year of therapy 2
Other parameters that should be monitored include complete blood count, lipid profile, and liver function tests, but hematocrit is the most critical laboratory value to monitor alongside PSA for safety during testosterone replacement therapy. Regular monitoring of hematocrit is essential to minimize the risk of adverse events associated with testosterone therapy 6.