From the Guidelines
The most accurate blood test for diagnosing hypogonadism is the total testosterone level measured in the morning, with a threshold of less than 300 ng/dL, as recommended by the American Urological Association 1. This should be combined with clinical evaluation and patient-reported symptoms, as the diagnosis of hypogonadism requires both a low testosterone measurement and the presence of select symptoms and/or signs. For accurate diagnosis, at least two separate morning testosterone measurements should be taken on different days, as testosterone levels can fluctuate 1. Additional tests that should be included are luteinizing hormone (LH) and follicle-stimulating hormone (FSH) to determine if the hypogonadism is primary (testicular failure) or secondary (pituitary/hypothalamic dysfunction). Some studies suggest that measuring free testosterone may also be valuable, as it represents the biologically active hormone that is not bound to proteins 1. However, the American Urological Association guideline recommends using total testosterone level as the primary diagnostic criterion 1. Morning testing is crucial because testosterone follows a diurnal rhythm with highest levels in the morning and lowest in the evening. Testing should be performed in a fasting state, and factors that can temporarily lower testosterone (such as acute illness, certain medications, or extreme stress) should be considered when interpreting results. It is also important to note that screening questionnaires are not an appropriate tool to identify candidates for testosterone therapy and should not be used at the expense of a full patient evaluation and laboratory testosterone measurement 1.
Some key points to consider when diagnosing hypogonadism include:
- Measuring total testosterone level in the morning, with a threshold of less than 300 ng/dL
- Combining testosterone measurement with clinical evaluation and patient-reported symptoms
- Taking at least two separate morning testosterone measurements on different days
- Considering additional tests, such as LH and FSH, to determine the underlying cause of hypogonadism
- Being aware of factors that can temporarily lower testosterone levels and considering them when interpreting results.
Overall, the diagnosis of hypogonadism requires a comprehensive approach that includes both laboratory testing and clinical evaluation, and the American Urological Association guideline provides a useful framework for clinicians to follow 1.
From the FDA Drug Label
Prior to initiating testosterone gel 1. 62%, confirm the diagnosis of hypogonadism by ensuring that serum testosterone has been measured in the morning on at least two separate days and that these concentrations are below the normal range.
The most accurate blood test for diagnosing hypogonadism is a serum testosterone test, which should be measured in the morning on at least two separate days.
- Key points:
- Measure serum testosterone in the morning
- Measure on at least two separate days
- Concentrations should be below the normal range to confirm diagnosis 2
From the Research
Diagnosis of Hypogonadism
To diagnose hypogonadism, a systematic approach is recommended, which includes:
- Establishing the presence of symptoms/signs of testosterone deficiency
- Considering other potential causes of manifestations
- Excluding conditions that transiently suppress testosterone 3
Blood Tests for Hypogonadism
The most accurate blood test for diagnosing hypogonadism is:
- Measuring fasting serum total testosterone in the morning on at least 2 separate days
- Measuring free testosterone by equilibrium dialysis or calculated free testosterone in men with conditions that alter sex hormone-binding globulin or serum total testosterone near lower limit of normal 3
Importance of Accurate Diagnosis
Accurate diagnosis of hypogonadism is crucial to guide management and identify the specific cause of hypogonadism, whether it is potentially reversible or an irreversible pathologic disorder 3, 4, 5
Testosterone Replacement Therapy
Testosterone replacement therapy (TRT) can be used to treat hypogonadism, and the evidence supporting TRT in improving body composition and sexual function is strong and consistent 4, 6