In evaluating suspected hypogonadism in men, which test should be ordered first?

In evaluating suspected hypogonadism in men, which test should be ordered first?

• A. LH
• B. FSH
• C. Early morning total serum testosterone
• D. Prolactin

Answer: (C)

Measuring serum total testosterone in the early morning is the best first step because testosterone has a clear diurnal pattern, peaking in the morning. A morning sample reduces the risk of falsely normal results and provides a reliable screen for hypogonadism. If the morning total testosterone is low, it should be confirmed with a second morning test to establish true biochemical hypogonadism. Once confirmed, you can use LH and FSH to distinguish primary testicular failure from secondary (hypothalamic-pituitary) causes, and check prolactin if pituitary pathology or hyperprolactinemia is a concern. If the morning value is normal, hypogonadism is unlikely, though symptoms persisting may warrant reevaluation or consideration of free testosterone if SHBG is suspected to be altered.

Measuring serum total testosterone in the early morning is the best first step because testosterone has a clear diurnal pattern, peaking in the morning. A morning sample reduces the risk of falsely normal results and provides a reliable screen for hypogonadism. If the morning total testosterone is low, it should be confirmed with a second morning test to establish true biochemical hypogonadism. Once confirmed, you can use LH and FSH to distinguish primary testicular failure from secondary (hypothalamic-pituitary) causes, and check prolactin if pituitary pathology or hyperprolactinemia is a concern. If the morning value is normal, hypogonadism is unlikely, though symptoms persisting may warrant reevaluation or consideration of free testosterone if SHBG is suspected to be altered.