From the Guidelines
To assess excessive testosterone injection, total testosterone should be measured, as it is the primary parameter used to monitor testosterone replacement therapy and provides a more standardized measurement across laboratories. When evaluating testosterone levels, it is essential to consider the timing of the measurement, as levels can fluctuate depending on the injection schedule. According to 1, for patients receiving testosterone injections, levels should be measured midway between injections, targeting a mid-normal value (500-600 ng/dL). Key points to consider when monitoring testosterone levels include:
- Total testosterone is the primary measurement used to monitor testosterone replacement therapy
- The target range for total testosterone in those on therapy is typically 400-700 ng/dL
- Levels consistently above 1000 ng/dL generally indicate excessive dosing
- Free testosterone can provide additional information but is less standardized across laboratories and not the primary monitoring parameter
- Blood samples should be drawn at the midpoint between injections to avoid measuring peak levels
- Testing should be performed after the patient has been on a stable dose for at least 4-6 weeks to allow hormone levels to reach steady state, as mentioned in 1. Excessive testosterone doses can lead to side effects including elevated red blood cell counts, acne, mood swings, and potential cardiovascular issues, which is why proper monitoring is essential, as highlighted in 1.
From the FDA Drug Label
Testosterone in plasma is 98 percent bound to a specific testosterone-estradiol binding globulin, and about 2 percent is free. Generally, the amount of this sex-hormone binding globulin in the plasma will determine the distribution of testosterone between free and bound forms, and the free testosterone concentration will determine its half-life
To assess excessive testosterone injection, free testosterone should be measured, as it is the active form of testosterone and determines its half-life.
- The free testosterone concentration is the most relevant measure, as it is the biologically active form of testosterone.
- Measuring total testosterone may not accurately reflect the amount of active testosterone, as it includes both bound and free forms. 2
From the Research
Testosterone Measurement
To assess excessive testosterone injection, it is essential to measure the correct type of testosterone. The two primary types of testosterone measurements are total testosterone and free testosterone.
Total Testosterone
- Total testosterone measures the total amount of testosterone in the blood, including both bound and free testosterone 3.
- Studies have shown that total testosterone measurement can be used as an initial test to evaluate male hypogonadism, but it may not be sensitive enough to reliably exclude hypogonadism in all cases 3.
- Total testosterone levels can be affected by various factors, including sex hormone-binding globulin (SHBG) abnormalities, and may not always accurately reflect the amount of bioactive testosterone in the body 4, 5.
Free Testosterone
- Free testosterone measures the amount of testosterone that is not bound to proteins in the blood and is considered the metabolically active fraction 4.
- Free testosterone is important in the diagnosis of many diseases, including disorders of androgen deficiency in men and androgen excess in women 4.
- Measurement of free testosterone can be useful in assessing excessive testosterone injection, as it can provide a more accurate reflection of the amount of bioactive testosterone in the body 4, 6.
Comparison of Total and Free Testosterone
- Studies have compared the effectiveness of total and free testosterone measurements in assessing testosterone levels, with some suggesting that free testosterone may be a more accurate indicator of bioactive testosterone 4, 3.
- However, total testosterone measurement is still widely used as an initial test to evaluate male hypogonadism, and free testosterone measurement may be reserved for cases where total testosterone levels are near the lower limit of normal or where SHBG abnormalities are suspected 3, 5.