From the Guidelines
For testosterone assessment, I recommend ordering a total testosterone test as the initial screening measure, as suggested by the most recent and highest quality study 1. This test measures both free and protein-bound testosterone in the blood and provides a comprehensive overview of testosterone status. If the total testosterone result is abnormal or if there are symptoms despite normal total testosterone, follow up with a free testosterone test, which measures only the biologically active unbound hormone. Morning collection (between 7-10 AM) is optimal as testosterone levels follow a diurnal pattern with peak levels in the morning. For patients on testosterone therapy, trough levels should be measured just before the next dose. In cases of suspected abnormal binding proteins, such as in obesity or liver disease, both total and free testosterone should be ordered simultaneously, as recommended by 1 and 1. These tests require a blood draw and results are typically available within a few days. Accurate testosterone measurement is essential for diagnosing hypogonadism, evaluating sexual dysfunction, monitoring hormone therapy, and investigating other endocrine disorders affecting reproductive health, as highlighted in 1, 1, and 1.
Some key points to consider when ordering testosterone lab tests include:
- Total testosterone levels should be measured using an accurate and reliable assay, as stated in 1 and 1.
- Free testosterone concentrations can be determined either directly from equilibrium dialysis assays or by calculations that use total testosterone, sex hormone binding globulin, and albumin concentrations, as recommended by 1 and 1.
- Further testing, such as luteinizing hormone and follicle-stimulating hormone levels, may be needed to determine if the patient has hypogonadism, as suggested by 1, 1, and 1.
Overall, the most recent and highest quality study 1 provides the best guidance for ordering testosterone lab tests, and its recommendations should be followed in clinical practice.
From the Research
Testosterone Lab Tests
To determine which testosterone lab test should be ordered, consider the following options:
- Total testosterone: measures the total amount of testosterone in the blood, including both free and bound testosterone 2
- Free testosterone: measures the amount of testosterone that is not bound to proteins in the blood and is available to the body's tissues 3, 4
- Calculated free testosterone: estimates the amount of free testosterone based on the total testosterone and sex hormone-binding globulin (SHBG) levels 5
Diagnostic Accuracy
Studies have shown that:
- Free testosterone levels are more accurate than total testosterone levels for diagnosing functional hypogonadism, especially in men with sexual symptoms 3
- Calculated free testosterone is more reliable than total testosterone for diagnosing late-onset hypogonadism in middle-aged and elderly males 5
- Measuring free testosterone can help reduce unnecessary endocrine evaluations by 50% 4
Measurement Considerations
When measuring testosterone levels:
- Total testosterone should be measured in a fasting state in the morning using a reliable assay, such as liquid chromatography tandem mass spectrometry 2
- Free testosterone levels should be measured in men with suspected alterations in binding protein concentrations or in whom total testosterone levels are only slightly above or slightly below the normal range 2