ABFM Practice Exam 2025 – Comprehensive Prep Resource

The first lab test to order for a male patient with suspected hypogonadism is early morning total serum testosterone. This is due to the diurnal variation of testosterone levels, which are highest in the early morning hours. Testing at this specific time helps to ensure that the testosterone levels are measured when they are at their peak, enhancing the likelihood of accurately diagnosing hypogonadism.

Measuring total serum testosterone provides an overall view of the testosterone in the body, detecting both free and bound testosterone. If the total testosterone level is low, further assessment, including free testosterone and other hormone levels (like LH and FSH), may be warranted to evaluate the underlying cause of hypogonadism.

In contrast, tests like free serum testosterone may provide additional information but are generally not the first step because total testosterone is more reliable for initial screening. LH and FSH levels, while important to evaluate the function of the testes and pituitary gland subsequently, do not provide direct information regarding testosterone levels initially. Testosterone binding globulin could be useful in specific contexts, but it is not necessary for the initial assessment of suspected hypogonadism. Thus, early morning total serum testosterone is the most appropriate first test in this situation.