Testosterone

Total testosterone should be drawn fasting, in the morning (before 10 AM) when levels peak. Confirm low testosterone with TWO morning samples drawn on separate days. Conditions that alter SHBG affect total T: Elevated SHBG (aging, liver disease, hyperthyroidism, anticonvulsants, estrogen) — total T may appear normal despite low free T. Low SHBG (obesity, diabetes, hypothyroidism, nephrotic syndrome, androgens) — total T may appear low despite adequate free T. When SHBG is abnormal, check free testosterone (equilibrium dialysis, not analog assay).

After confirming low total T on two morning samples: Check LH and FSH to classify — Primary hypogonadism (high LH/FSH): testicular failure (Klinefelter, orchitis, chemotherapy, radiation). Secondary hypogonadism (low/normal LH/FSH): pituitary/hypothalamic cause. Additional workup: prolactin (prolactinoma), iron/ferritin (hemochromatosis), cortisol if adrenal insufficiency suspected, pituitary MRI if prolactin elevated or very low T. Also assess for reversible causes: obesity, opioids, glucocorticoids, sleep apnea, and chronic illness.

Indications: Confirmed low T (<300 ng/dL on two AM samples) PLUS symptoms (low libido, erectile dysfunction, fatigue, decreased muscle mass, depressed mood). Before starting: Check hematocrit, PSA, lipids. Contraindications: desire for fertility (exogenous T suppresses spermatogenesis), untreated severe OSA, hematocrit >50%, uncontrolled heart failure, PSA >4 without urology evaluation, active prostate/breast cancer. Monitoring: T levels at 3-6 months, hematocrit every 6-12 months (stop if >54%), PSA at 3-12 months then annually, DEXA if osteoporosis.