What additional labs should be ordered for a male patient beyond testosterone?

Essential Laboratory Testing Beyond Testosterone in Male Patients

When evaluating a male patient with suspected testosterone deficiency, you must measure luteinizing hormone (LH) in all cases, followed by prolactin if LH is low or low-normal, hemoglobin/hematocrit, and PSA in men over 40 years. 1

Core Laboratory Panel (Required for All Patients)

Luteinizing Hormone (LH)

• Measure serum LH in every patient with confirmed low testosterone 1
• LH levels determine whether hypogonadism is primary (testicular) versus secondary (hypothalamic-pituitary) 1
• Low or low-normal LH with low testosterone indicates secondary hypogonadism and triggers additional pituitary evaluation 1

Prolactin

• Measure prolactin only when testosterone is low AND LH is low or low-normal 1
• Repeat elevated prolactin measurements to exclude spurious results 1
• Persistently elevated prolactin requires endocrinology referral for possible prolactinoma 1
• Critical threshold: Total testosterone <150 ng/dL with low/low-normal LH warrants pituitary MRI regardless of prolactin level 1

Hemoglobin/Hematocrit

• Measure baseline hemoglobin and hematocrit before initiating testosterone therapy 1
• Withhold testosterone if hematocrit exceeds 50% until etiology is investigated 1
• This baseline is essential for monitoring polycythemia risk during treatment 1

Prostate-Specific Antigen (PSA)

• Measure PSA in all men over 40 years before starting testosterone therapy 1
• Repeat elevated PSA to rule out spurious elevation 1
• This screening minimizes risk of prescribing testosterone to men with occult prostate cancer 1

Conditional Laboratory Testing (Based on Clinical Presentation)

Follicle-Stimulating Hormone (FSH)

• Measure FSH in men interested in fertility preservation 1
• Elevated FSH with low testosterone (hypergonadotropic hypogonadism) indicates impaired spermatogenesis 1
• Consider semen analysis when FSH is elevated 1

Estradiol

• Measure estradiol only in patients presenting with breast symptoms or gynecomastia 1
• Elevated baseline estradiol requires endocrinology referral 1
• Not routinely indicated in asymptomatic patients 1

Cardiovascular Risk Assessment

• Assess lipid panel and glucose/HbA1c to evaluate ASCVD risk factors 1
• Screen for dyslipidemia, hypertension, and diabetes before testosterone therapy 1
• Men with diabetes and hypogonadism symptoms should have morning total testosterone measured 1

Clinical Algorithm for Laboratory Ordering

Step 1: Confirm low testosterone (<300 ng/dL on two early morning measurements) 1, 2

Step 2: Order mandatory baseline labs:

• LH 1
• Hemoglobin/hematocrit 1
• PSA (if age >40) 1

Step 3: If LH is low or low-normal:

• Add prolactin 1
• If testosterone <150 ng/dL, proceed directly to pituitary MRI 1

Step 4: Add conditional labs based on presentation:

• FSH if fertility concerns 1
• Estradiol if breast symptoms/gynecomastia 1
• Lipids and glucose for cardiovascular risk stratification 1

Common Pitfalls to Avoid

• Do not skip LH measurement—it is the single most important test to differentiate primary from secondary hypogonadism and guides all subsequent evaluation 1
• Do not measure prolactin in patients with normal or elevated LH—this wastes resources and provides no diagnostic value 1
• Do not delay pituitary MRI when testosterone is <150 ng/dL with low/low-normal LH—non-secreting adenomas may be present even with normal prolactin 1
• Do not start testosterone therapy without baseline hematocrit—you cannot monitor for polycythemia without a reference point 1
• Do not measure estradiol routinely—reserve this for symptomatic patients only 1