What other laboratory tests should be ordered in addition to testosterone levels?

Laboratory Testing for Low Testosterone (7.1 ng/dL)

With a testosterone level of 7.1 ng/dL (assuming this is 71 ng/dL or 710 ng/dL based on typical units), you must order luteinizing hormone (LH), hemoglobin/hematocrit, and PSA (if patient is over 40 years old) as the essential baseline tests before initiating any testosterone therapy. 1, 2

Essential Initial Laboratory Tests

Luteinizing Hormone (LH)

• Measure serum LH in all patients with confirmed low testosterone to determine the etiology of hypogonadism 1, 2
• Low or inappropriately normal LH with low testosterone indicates secondary (central) hypogonadism from hypothalamic-pituitary dysfunction 2
• Elevated LH with low testosterone indicates primary (testicular) hypogonadism 2
• This distinction is critical as it determines whether additional pituitary evaluation is needed 1

Hemoglobin and Hematocrit

• Baseline hemoglobin/hematocrit measurement is mandatory before starting testosterone therapy 1, 3
• If hematocrit exceeds 50%, withhold testosterone therapy until the etiology is formally investigated 1
• This is a strong recommendation with Grade A evidence to prevent polycythemia complications 1

Prostate-Specific Antigen (PSA)

• PSA must be measured in men over 40 years of age prior to testosterone therapy to exclude occult prostate cancer 1, 3
• If PSA is elevated at baseline, repeat the test to rule out spurious elevation 1
• Two elevated PSA levels warrant formal evaluation including reflex testing (4K or phi) and potentially prostate biopsy with/without MRI before initiating therapy 1

Secondary Testing Based on LH Results

If LH is Low or Low/Normal (Secondary Hypogonadism)

Serum Prolactin

• Measure prolactin only in patients with low testosterone AND low/normal LH 1, 2
• If prolactin is elevated, repeat the measurement to exclude spurious results 1, 2
• Persistently elevated prolactin requires endocrinology referral and evaluation for prolactinoma 1, 2

Pituitary MRI

• Men with total testosterone <150 ng/dL combined with low or low/normal LH should undergo pituitary MRI regardless of prolactin levels, as non-secreting adenomas may be present 1, 2
• This is critical to avoid missing pituitary tumors that present with central hypogonadism 1, 4

Additional Testing for Specific Clinical Scenarios

Fertility Concerns

• Measure serum follicle-stimulating hormone (FSH) in men interested in fertility preservation 1, 2
• Elevated FSH with low testosterone suggests impaired spermatogenesis and warrants consideration of semen analysis 1, 2
• Patients with severe oligospermia (<5 million sperm/mL) or non-obstructive azoospermia should be offered reproductive genetics testing including karyotype and Y-chromosome microdeletion analysis 1

Breast Symptoms or Gynecomastia

• Measure serum estradiol only if the patient presents with breast symptoms or gynecomastia prior to testosterone therapy 1, 2
• Elevated baseline estradiol requires endocrinology referral 1, 2

Cardiovascular Risk Assessment

• Assess all testosterone deficient patients for atherosclerotic cardiovascular disease (ASCVD) risk factors including dyslipidemia, hypertension, diabetes, and smoking status 1
• This is a strong recommendation with Grade A evidence 1

Common Pitfalls to Avoid

• Do not skip the repeat testosterone measurement: Diagnosis requires at least two early morning testosterone measurements, preferably using the same laboratory and method 1, 3
• Do not measure prolactin in all patients: Only measure it when LH is low or low/normal, as this indicates central hypogonadism where prolactinomas are a concern 1, 2
• Do not forget PSA in men over 40: This is a clinical principle to minimize prescribing testosterone to men with occult prostate cancer 1
• Do not initiate therapy with hematocrit >50%: This requires investigation before starting testosterone to prevent complications 1