When measuring testosterone levels, it is critical to determine the levels of both free and total testosterone to understand the cause of any observed symptoms of deficiency (Khosla et al 2008).
Because of difficulties with equipment standardization and inter-laboratory variability, it is recommended that physicians consistently use the same local laboratories and gain familiarity with the accuracy, precision and definition of normal values for the assays offered in their communities (Morales et al 2010).
Alkaline phosphatase, hemoglobin and hematocrit, and creatinine may vary depending on the patient's current sex hormone configuration. Several factors contribute to these differences, bone mass, muscle mass, number of myocytes, presence or lack of menstruation, and erythropoetic effect of testosterone. Many transgender men do not menstruate, and those with male-range testosterone levels will experience an erythropoetic effect. As such an amenorrheic transgender man taking testosterone, registered as female and with hemoglobin/hematocrit in the range between the male and female lower limits of normal, may be considered to have anemia, even though the lab report may not indicate so. Conversely, the lack of menstruation, and presence of exogenous testosterone make it reasonable to use the male-range upper limit of normal for hemoglobin/hematocrit. Using the male-range upper limit of normal for alkaline phosphatase and creatinine may also be appropriate for transgender men due to increased bone and muscle mass, respectively. In these cases the provider should reference the male normal ranges for their lab.
Using appropriate tests for monitoring hormone therapy is crucial in establishing the appropriate dosing regimen. This reduces the chance of undesirable side effects and maximizes beneficial effects. For example, excessive use of androgens (testosterone, androstenedione, DHEA, and testosterone derivatives) can activate subclinical prostate tumors which are androgen-dependent. Monitoring is especially important in older males. By the age of 70, at least 50% of men have subclinical prostate cancer. These men are especially susceptible to prostate growth stimulation by androgens.