A repeat testosterone level is appropriate for this older patient with fatigue, weakness, and erectile dysfunction (ED). Men with specific signs and symptoms of androgen deficiency should be evaluated by measuring morning total testosterone level as the initial diagnostic test. Men with low or low-normal testosterone levels should have confirmatory testing before initiating testosterone therapy, and further evaluation of the cause of hypogonadism should be pursued before treatment is started, if indicated. If the repeat serum total testosterone level is more equivocal (200-350 ng/dL [6.9-12.1 nmol/L]) or if a sex hormone–binding globulin abnormality is likely in the patient being evaluated, a serum free testosterone level by equilibrium dialysis or a calculated serum free testosterone level can determine whether hypogonadism is truly present.

When hypogonadism is confirmed, the next step is to determine whether the patient has primary or secondary hypogonadism by measuring the luteinizing hormone (LH) and follicle-stimulating hormone (FSH) levels. Primary hypogonadism is indicated by supranormal LH and FSH levels. If secondary hypogonadism is confirmed by inappropriately normal or low LH and FSH levels, measurement of the serum prolactin level to evaluate for hyperprolactinemia and iron saturation level (transferrin saturation and ferritin levels) to exclude hemochromatosis should be performed to assess for the possible cause. In addition, the presence of any additional pituitary hormone deficiencies should be assessed.

An MRI of the pituitary gland should be ordered to exclude hypothalamic or pituitary masses as the cause of decreased gonadotropin production and secretion if any symptoms consistent with mass effect are present, including headaches, visual field changes, a serum total testosterone level less than 150 ng/dL (5.2 nmol/L), an increased prolactin level, or any additional pituitary hormonal deficiencies.

Testosterone replacement in older men should be given only in the setting of hypogonadism that is based on symptoms (such as decreased libido and generalized muscle weakness) and morning serum total testosterone levels lower than 200 ng/dL (6.9 nmol/L) on at least two separate occasions. Therefore, this patient needs confirmation on repeat testing before considering testosterone replacement therapy.