The patient has a clinical history suspicious for hemochromatosis and should be further evaluated by measuring serum transferrin saturation and ferritin levels. The patient has hypogonadism based on his clinical symptoms of decreased libido and erectile dysfunction, associated with a low morning serum testosterone level. A hypogonadotropic etiology is indicated by his low luteinizing and follicle-stimulating hormone levels. Causes of hypogonadotropic hypogonadism include infiltrative diseases such as hemochromatosis, sarcoidosis, cancer metastatic to the pituitary, and lymphoma. Pituitary tumors that impair gonadotropin function may also be a cause. This patient has several clinical findings suggestive of possible hemochromatosis, including a report of arthralgia and hepatomegaly on physical examination. Therefore, the next step in evaluation of this patient's hypogonadotropic hypogonadism is measurement of serum ferritin level and transferrin saturation to evaluate for possible hemochromatosis.

The cause of hypogonadism must be evaluated prior to the initiation of testosterone replacement. If testosterone therapy is started without testing for hemochromatosis, the diagnosis may be missed.

Although genetic disorders such as Klinefelter syndrome (47,XXY) may cause hypogonadism, patients with this syndrome have hypergonadotropic hypogonadism with elevated luteinizing and follicle-stimulating hormone values, unlike this patient. Therefore, karyotyping is not indicated.

A testicular ultrasound is used to evaluate the cause of primary testicular failure and is not indicated in the evaluation of hypogonadotropic hypogonadism. This patient's low gonadotropin levels indicate either a hypothalamic or pituitary disorder, instead of testicular disease. Although hemochromatosis may also directly affect testicular function in addition to its central hypogonadal effect, testicular ultrasound is not helpful in establishing the diagnosis of hemochromatosis as a cause of hypogonadism.