From the Guidelines
For a 16-year-old male with hypogonadism, I recommend drawing total testosterone, luteinizing hormone (LH), follicle-stimulating hormone (FSH), and prolactin as the initial laboratory evaluation. This approach is supported by the most recent and highest quality study, which emphasizes the importance of measuring total testosterone levels, as well as LH and FSH, to determine the underlying cause of hypogonadism 1.
Initial Laboratory Evaluation
The initial laboratory evaluation should include:
- Total testosterone
- Luteinizing hormone (LH)
- Follicle-stimulating hormone (FSH)
- Prolactin Additional tests should include:
- Complete blood count
- Comprehensive metabolic panel
- Thyroid function tests (TSH, free T4)
- A bone age assessment
Further Evaluation
If the initial tests suggest primary hypogonadism (elevated LH/FSH with low testosterone), karyotyping should be performed to rule out Klinefelter syndrome. For suspected secondary hypogonadism (low/normal LH/FSH with low testosterone), additional pituitary hormone testing (growth hormone, cortisol, ACTH) and brain MRI with focus on the pituitary and hypothalamus are warranted. Morning samples are preferred for hormone testing as testosterone levels follow a diurnal pattern with highest levels in the morning, as recommended by the American Urological Association guideline 1.
Importance of Early Diagnosis and Management
These tests help differentiate between primary hypogonadism (testicular failure) and secondary hypogonadism (pituitary/hypothalamic dysfunction), which guides appropriate treatment. Early diagnosis and management are crucial during adolescence to prevent complications like delayed puberty, poor bone mineralization, and psychosocial issues. The diagnosis of testosterone deficiency requires both a low testosterone measurement as well as the presence of select symptoms and/or signs, as outlined in the guideline 1.
From the FDA Drug Label
DOSAGE AND ADMINISTRATION Prior to initiating testosterone enanthate injection, confirm the diagnosis of hypogonadism by ensuring that serum testosterone concentrations have been measured in the morning on at least two separate days and that these serum testosterone concentrations are below the normal range
- To diagnose hypogonadism in a 16-year-old male, the following lab should be drawn:
- Serum testosterone concentrations, measured in the morning on at least two separate days 2 Note that other labs such as hemoglobin and hematocrit may be checked periodically for polycythemia in patients who are receiving high doses of androgens, and X-ray examinations of bone age should be made during treatment of pre-pubertal males to determine the rate of bone maturation and the effects of androgen therapy on the epiphyseal centers 2, but these are not directly relevant to the initial diagnosis of hypogonadism.
From the Research
Laboratory Tests for Hypogonadism
To diagnose hypogonadism in a 16-year-old male, the following laboratory tests are recommended:
- Morning serum total testosterone levels on at least two separate days 3
- 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
- Serum luteinizing hormone (LH) and follicle-stimulating hormone (FSH) levels to distinguish between primary (hypergonadotropic) and secondary (hypogonadotropic) hypogonadism 4, 5
- Serum prolactin to rule out secondary hypogonadism 5
- Sex hormone-binding globulin (SHBG) to estimate free testosterone 5
Rationale for Laboratory Tests
These laboratory tests are essential to confirm the diagnosis of hypogonadism and to guide management. The measurement of morning serum total testosterone levels is crucial to establish the presence of hypogonadism 3. The assessment of LH and FSH levels helps to identify the specific cause of hypogonadism and whether it is potentially reversible or an irreversible pathologic disorder 4, 5. The measurement of serum prolactin and SHBG is also important to rule out secondary hypogonadism and to estimate free testosterone, respectively 5.
Additional Considerations
In addition to these laboratory tests, a physical examination and medical history are also essential to diagnose hypogonadism. The diagnosis of hypogonadism should be based on a combination of clinical signs and symptoms, as well as laboratory confirmation 4, 3.