What labs should I order for a new patient who is already on testosterone replacement therapy when I take over their care?

Laboratory Monitoring for Patients on Testosterone Replacement Therapy

When taking over care of a patient already on testosterone replacement therapy, you must order: serum testosterone level (morning, 8-10 AM), hemoglobin/hematocrit, PSA (if age >40), and luteinizing hormone (LH) at baseline. 1

Essential Baseline Laboratory Tests

Core Monitoring Panel

• Serum Total Testosterone: Obtain early morning sample (8-10 AM) to account for diurnal variation; this establishes whether current therapy is achieving therapeutic levels in the mid- to upper-normal range (264-916 ng/dL). 1

• Hemoglobin/Hematocrit: Mandatory baseline measurement to detect polycythemia; if hematocrit exceeds 50%, investigate the etiology before continuing therapy, and if hematocrit rises above 54% on treatment, dose reduction or temporary discontinuation is warranted. 1, 2

• PSA (Prostate-Specific Antigen): Required for men over 40 years of age to exclude occult prostate cancer; if elevated at baseline, repeat testing is recommended to rule out spurious elevation before continuing therapy. 1

• Serum Luteinizing Hormone (LH): Helps establish the etiology of testosterone deficiency (primary vs. secondary hypogonadism) and guides whether additional endocrine workup is needed. 1

Additional Baseline Tests Based on Clinical Context

• Serum Prolactin: Measure if LH is low or low-normal, as this screens for hyperprolactinemia and potential pituitary tumors; persistently elevated prolactin requires endocrinology referral. 1

• Lipid Panel: Optional but recommended given the association between testosterone deficiency and cardiovascular risk factors; assess for dyslipidemia as part of ASCVD risk stratification. 1

• Serum Estradiol: Only if the patient presents with breast symptoms or gynecomastia, as elevated estradiol warrants endocrinology referral. 1

• FSH (Follicle-Stimulating Hormone): If fertility is a concern or if the patient is interested in future reproduction, as testosterone therapy suppresses spermatogenesis; elevated FSH with low testosterone indicates primary testicular failure. 1

Ongoing Monitoring Schedule

Initial Follow-Up (1-2 Months)

• First follow-up visit at 1-2 months to assess treatment efficacy and consider dose adjustment if clinical response is inadequate with suboptimal testosterone levels. 1

• Measure serum testosterone level (morning sample), hemoglobin/hematocrit, and PSA at this visit. 1

Subsequent Monitoring (3-6 Month Intervals First Year, Then Yearly)

• Visits every 3-6 months during the first year, then annually thereafter if stable. 1

• At each visit, measure: serum testosterone (to confirm therapeutic levels), PSA, and hemoglobin/hematocrit. 1

• Assess symptomatic response including libido, erectile function, energy, mood, and voiding symptoms. 1

• Perform digital rectal examination at each visit to monitor prostate health. 1

Critical Safety Thresholds and Actions

Hematocrit Management

• Hematocrit >54% requires intervention: reduce dose or temporarily discontinue therapy; injectable testosterone formulations carry the highest risk for polycythemia. 1

• Consider phlebotomy if hematocrit rises above the reference range despite dose reduction. 1

PSA Monitoring

• PSA increase >1.4 μg/L per year or absolute PSA elevation raising suspicion for prostate cancer warrants urological evaluation with potential reflex testing (4K score, phi) and prostate biopsy consideration. 1, 3

• Shared decision-making approach for ongoing PSA testing in men maintaining normal testosterone levels, following AUA Early Detection of Prostate Cancer Guidelines. 1

Common Pitfalls to Avoid

• Do not obtain random testosterone levels: Only early morning (8-10 AM) samples are valid due to diurnal variation; compliance with proper timing is notoriously poor (only 9% in one study). 4, 5

• Do not ignore fertility implications: Exogenous testosterone suppresses spermatogenesis; discuss this with all patients of reproductive age and consider stopping therapy well in advance of conception attempts. 1

• Do not overlook sleep apnea history: Testosterone therapy can exacerbate or precipitate sleep apnea, particularly with higher doses; assess at baseline and monitor symptoms. 1

• Do not continue therapy without monitoring: Failure to track hematocrit can lead to dangerous polycythemia; failure to monitor PSA may miss occult prostate cancer progression. 1, 2