What tests should be done to investigate hypogonadism in an 18-year-old?

Diagnostic Workup for Hypogonadism in an 18-Year-Old

The diagnosis of hypogonadism in an 18-year-old requires at least two separate morning total testosterone measurements, followed by luteinizing hormone (LH) and follicle-stimulating hormone (FSH) testing to determine the etiology, and additional targeted testing based on these initial results. 1

Initial Diagnostic Tests

Primary Testing

• Total testosterone levels: Must be measured on at least two separate occasions in the early morning (8-10 AM) using the same laboratory and testing method 1, 2

  • Threshold for low testosterone: consistently <300 ng/dL
  • Morning testing is essential due to significant diurnal variation 2

• Free testosterone: Should be measured alongside total testosterone, especially if obesity is present 1, 2

  • Free testosterone index (total testosterone/SHBG ratio) <0.3 indicates hypogonadism 1

Secondary Testing (After Confirming Low Testosterone)

• Luteinizing hormone (LH) and follicle-stimulating hormone (FSH) 1
  • Helps distinguish between primary (testicular) and secondary (pituitary-hypothalamic) hypogonadism
  • Low/normal LH with low testosterone suggests secondary hypogonadism
  • Elevated LH with low testosterone suggests primary hypogonadism

Additional Testing Based on Initial Results

If Low/Normal LH with Low Testosterone

• Serum prolactin: Essential to screen for hyperprolactinemia 1

  • If elevated, repeat to confirm and consider pituitary imaging

• Pituitary MRI: Indicated if total testosterone <150 ng/dL with low/normal LH, regardless of prolactin levels 1

  • Helps identify non-secreting pituitary adenomas

• Iron saturation: To evaluate for hemochromatosis 1

For All Patients with Confirmed Hypogonadism

• Serum estradiol: Especially if breast symptoms or gynecomastia are present 1

• Bone mineral density test: Consider if hypogonadism is confirmed 1

• Complete metabolic panel: To assess liver and kidney function

• Hemoglobin/hematocrit: As baseline before potential testosterone therapy

Special Considerations for 18-Year-Old Patients

• Semen analysis: If fertility is a concern 1

• Anti-Müllerian hormone (AMH): May be helpful in cases where diagnosis is challenging 3

• GnRH stimulation test: Consider if diagnosis remains unclear, especially with history of delayed puberty or cryptorchidism 3

Clinical Assessment

Symptoms to Document

• Reduced energy, endurance, and physical performance
• Fatigue
• Visual field changes (bitemporal hemianopsia)
• Anosmia (may suggest Kallmann syndrome)
• Depression, reduced motivation, poor concentration
• Impaired memory, irritability
• Infertility
• Reduced sex drive
• Changes in erectile function 1

Physical Examination

• General body habitus
• Virilization status (body hair patterns in androgen-dependent areas)
• BMI or waist circumference
• Gynecomastia
• Testicular evaluation (presence, size, consistency, masses)
• Varicocele presence
• Pubertal development (Tanner staging) 1

Common Pitfalls to Avoid

1. Testing at incorrect times: Afternoon or evening testing can result in falsely low readings 2

2. Diagnosing based on a single measurement: This can lead to misdiagnosis and inappropriate treatment 2, 4

3. Failing to measure LH/FSH: Only 12% of men have gonadotropins measured prior to testosterone therapy initiation, leading to potential misclassification of hypogonadism type 4

4. Not considering secondary causes: Conditions like hemochromatosis, pituitary tumors, or medications can cause hypogonadism 1

5. Ignoring SHBG levels: SHBG can be altered by liver disease, obesity, or thyroid disorders, affecting total testosterone interpretation 2

By following this comprehensive diagnostic approach, clinicians can accurately diagnose hypogonadism in an 18-year-old patient and determine the appropriate treatment strategy based on the underlying etiology.