* Total testosterone has lower sensitivity for hypogonadism in men aged > 50 years. If the test for free and weakly bound testosterone is available, levels are measured. If not, levels are calculated.

† Recommended by some physicians.

CT = computed tomography; Fe = iron; FSH = follicle-stimulating hormone; GnRH = gonadotropin-releasing hormone; LH = luteinizing hormone; MRI = magnetic resonance imaging.