TRT Blood Work: What to Test, When to Test, and What the Numbers Mean

# TRT Blood Work: What to Test, When to Test, and What the Numbers Mean

Starting TRT without regular blood work is like flying blind. Your lab values tell you whether the therapy is working, whether your body is tolerating it, and whether any adjustments are needed. This guide covers everything you need to know about monitoring your health on testosterone replacement therapy.

Why Blood Work Matters on TRT

Testosterone doesn't act in isolation. When you introduce exogenous testosterone, your body responds in complex ways: estrogen levels change, red blood cell production increases, your natural testosterone production shuts down. Blood work lets your physician track all of this and optimize your protocol accordingly.

Skipping labs isn't just negligent — it's inefficient. Patients who monitor regularly reach their optimal protocol faster and experience fewer problems than those who guess.

The Core TRT Panel

### Total Testosterone The primary metric. Most men on TRT aim for levels between 600–1,000 ng/dL, though the optimal range varies by individual. Higher isn't always better — levels above 1,200 ng/dL increase aromatization to estrogen and raise hematocrit risk.

### Free Testosterone The bioavailable fraction that actually enters cells. Around 1–3% of total testosterone is free. Men with high SHBG can have acceptable total T but low free T — which means the therapeutic effect is diminished. Target: upper half of the reference range (roughly 15–25 ng/dL).

### Estradiol (E2) Testosterone aromatizes to estrogen. As testosterone levels rise, so does estrogen. Elevated estradiol causes water retention, mood changes, reduced libido, and can lead to gynecomastia (breast tissue growth). Most men feel best with E2 between 20–30 pg/mL, though some tolerate higher levels without symptoms. Request the sensitive assay (LC/MS/MS method) — the standard assay is less accurate for men.

### Hematocrit and Hemoglobin Testosterone stimulates red blood cell production (erythropoiesis). Elevated hematocrit thickens the blood, increasing cardiovascular risk. Target hematocrit: below 52–54%. If it rises above this, dose adjustment, donation, or therapeutic phlebotomy may be needed.

### SHBG (Sex Hormone-Binding Globulin) SHBG binds testosterone, making it unavailable. Men with high SHBG get less free T from the same total T. Low SHBG leads to rapid clearance of testosterone and more pronounced fluctuations between doses. SHBG guides dosing frequency — high SHBG may benefit from weekly injections; low SHBG often does better with more frequent, smaller doses.

### LH and FSH Luteinizing hormone and follicle-stimulating hormone are suppressed by exogenous testosterone. Expect near-zero values on TRT — this confirms you're not producing endogenous testosterone while on therapy. If you care about fertility, this is why hCG or HMG adjuncts are discussed.

### PSA (Prostate-Specific Antigen) Important for men over 40. TRT doesn't cause prostate cancer, but it can accelerate existing, undetected disease. Baseline PSA before starting, then monitor annually. A significant rise (>1.4 ng/mL over 12 months, or absolute value above 4.0) warrants urological evaluation.

### Comprehensive Metabolic Panel (CMP) Covers liver enzymes (ALT, AST), kidney function (creatinine, BUN), and electrolytes. Oral testosterone can cause liver stress — injectable testosterone does not typically affect liver values. Still worth monitoring annually.

### Lipid Panel Testosterone tends to lower HDL (good cholesterol) and can affect LDL. The impact is generally modest with physiologic replacement doses, but warrants monitoring — especially if you have baseline cardiovascular risk factors.

When to Test

Before starting TRT: Complete baseline panel including everything above. This establishes your starting point and screens for conditions (elevated PSA, polycythemia, liver disease) that might affect treatment decisions.

6–8 weeks after starting or changing dose: First follow-up. Testosterone levels take 4–6 weeks to fully stabilize after a dose change. Testing too early gives misleading numbers. Key values at this point: total T, free T, E2, hematocrit.

3 months: Second follow-up. Full panel. By now your protocol should be dialed in and side effects (if any) apparent. This is typically when dose adjustments or anastrozole decisions are made.

Every 6 months (stable patient): Once your protocol is optimized and stable, semi-annual labs are appropriate for most men. High-risk patients (elevated hematocrit, cardiovascular history, elevated PSA) should continue quarterly monitoring.

Annually: Full comprehensive panel including PSA and lipids.

Timing Your Blood Draw

Test at trough — the lowest point in your testosterone cycle, just before your next scheduled injection. This gives the most accurate picture of your baseline level and prevents artificially elevated readings from influencing dose decisions.

If you inject once weekly, test on the morning of your injection day, before injecting. If you inject more frequently (twice weekly or daily), trough is less critical because levels are more stable — but consistency in timing still matters for apples-to-apples comparison over time.

Interpreting Your Results

Testosterone in range, feeling good: Protocol is working. Continue and monitor.

Testosterone in range, still symptomatic: Check free testosterone and SHBG. High SHBG may require protocol adjustment. Also review sleep, stress, thyroid function, and vitamin D — these affect how you feel independent of testosterone levels.

High estradiol with symptoms (water retention, mood changes, low libido): Discuss anastrozole with your physician. Note: not all men need an AI — many tolerate higher E2 without symptoms. Treat symptoms, not just numbers.

Rising hematocrit (above 52%): Increase injection frequency (smaller, more frequent doses reduce hematocrit drive), consider therapeutic phlebotomy, or discuss dose reduction.

PSA increase: Pause TRT and refer to urology for evaluation before continuing.

The Marrow Approach

At Marrow, we require baseline labs before prescribing and build monitoring into every patient's protocol. Your physician reviews your results, adjusts your prescription if needed, and communicates changes clearly. Labs aren't a bureaucratic hurdle — they're how we ensure what we're doing is actually working for you.

Good TRT management is collaborative. Bring your symptoms, your lab trends, and your questions. The numbers and the way you feel together tell the full story.