TRT blood test guide: every marker you need to track.

Why blood work on TRT is non-negotiable

Testosterone replacement therapy is a hormone intervention. Unlike most supplements, exogenous testosterone directly alters the endocrine system — it increases red blood cell production (erythropoiesis), converts to estradiol via aromatization, suppresses gonadotropins (LH and FSH), affects lipid metabolism, and stimulates prostate tissue[1]. Each of these effects has blood markers that allow you to monitor them objectively.

The Endocrine Society's 2018 clinical practice guidelines explicitly recommend monitoring hematocrit, testosterone levels, and PSA at 3-6 months after initiation, and every 6-12 months thereafter[2]. Many experienced TRT clinicians monitor a broader panel. This guide covers every marker worth tracking and explains why.

The essential TRT blood panel

Total testosterone

Total testosterone measures all testosterone in your blood — both bound (to SHBG and albumin) and unbound (free). It is the primary measure used to confirm that TRT is achieving therapeutic levels. The Endocrine Society defines male hypogonadism as total testosterone consistently below 300 ng/dL (10.4 nmol/L)[2].

Optimal range on TRT: Most TRT clinicians aim for trough total testosterone between 500-900 ng/dL. "Trough" means the lowest point in your dosing cycle — typically the morning of your next injection. Peak values will be higher, often 1.5-2x the trough. If your trough is above 900 ng/dL, the dose is likely higher than necessary; if below 400 ng/dL, it's likely insufficient.

Free testosterone

Free testosterone represents the 2-3% of total testosterone that is unbound and biologically active. It is arguably more clinically relevant than total testosterone because it reflects the hormone actually available to tissues[3]. Free testosterone can be measured directly (equilibrium dialysis is the gold standard) or calculated from total testosterone, SHBG, and albumin.

Optimal range on TRT: The reference range varies by assay, but generally 15-25 pg/mL (by direct measurement) or within the upper quartile of the lab's reference range. If total testosterone is adequate but free testosterone is low, elevated SHBG is usually the explanation.

Estradiol (E2)

Testosterone converts to estradiol via the aromatase enzyme, which is concentrated in adipose tissue. On TRT, estradiol rises in rough proportion to testosterone[4]. Some estradiol is essential — it plays important roles in bone density, libido, joint health, and cardiovascular protection. But excessively high estradiol can cause water retention, mood instability, nipple sensitivity, and gynecomastia.

Critical note on testing: Use the sensitive estradiol assay (LC-MS/MS method), not the standard immunoassay. The standard assay is designed for female reference ranges and can produce inaccurate readings in men. Most labs offer this as "Estradiol, Sensitive" or "Estradiol by LC-MS/MS."

Optimal range on TRT: 20-50 pg/mL is the generally accepted target range. Below 20 pg/mL, men often report joint pain, low libido, and dry skin. Above 50-60 pg/mL, estrogen-related side effects become more common.

SHBG (sex hormone-binding globulin)

SHBG is a protein that binds testosterone, reducing its bioavailability. High SHBG means more testosterone is bound and less is free. Low SHBG means more free testosterone but also faster clearance. On TRT, SHBG typically decreases modestly[5]. Understanding your SHBG helps interpret the relationship between total and free testosterone and can inform injection frequency (men with low SHBG often benefit from more frequent, smaller doses).

Hematocrit and hemoglobin

This is the most important safety marker on TRT. Testosterone stimulates erythropoietin (EPO) production and directly stimulates red blood cell precursors in the bone marrow, increasing red blood cell mass[6]. Hematocrit — the percentage of blood volume occupied by red blood cells — reliably rises on TRT, typically by 3-5 percentage points.

Elevated hematocrit increases blood viscosity and, in observational data, has been associated with increased risk of thromboembolic events (blood clots, stroke, pulmonary embolism)[7].

PSA (prostate-specific antigen)

PSA is a protein produced by the prostate gland. Historically, there was concern that testosterone therapy would increase prostate cancer risk. Current evidence does not support this — multiple meta-analyses and the Testosterone Trials (TTrials) have not shown an increase in prostate cancer incidence with TRT[8][9]. However, testosterone does stimulate prostate growth, and monitoring PSA remains standard of care.

What to watch: A baseline PSA before starting TRT is essential. A mild rise (0.3-0.5 ng/mL) in the first 6-12 months is expected and not concerning. A rise exceeding 1.4 ng/mL above baseline within 12 months, any PSA above 4.0 ng/mL, or a PSA velocity exceeding 0.75 ng/mL per year warrants urological evaluation[2].

Lipid panel

TRT has modest effects on lipids. The most consistent change is a mild decrease in HDL cholesterol, typically 5-10%[10]. LDL may change modestly in either direction. Triglycerides are generally unaffected or slightly improved. Supraphysiological doses produce more adverse lipid effects than therapeutic doses. ApoB, if available, provides a more accurate assessment of atherogenic risk than LDL alone.

Liver enzymes: ALT and AST

Injectable testosterone (cypionate, enanthate) has minimal hepatotoxicity because it bypasses first-pass liver metabolism. Oral testosterone formulations (methyltestosterone, historically) were hepatotoxic, but modern oral testosterone undecanoate (Jatenzo) has a safer hepatic profile[11]. Monitoring ALT and AST on injectable TRT is precautionary and typically unremarkable. However, elevated liver enzymes from other causes (alcohol, NAFLD, medications) are worth tracking alongside your TRT panel.

Prolactin

Prolactin is not always included in TRT panels, but it should be. Elevated prolactin can cause sexual dysfunction, gynecomastia, and mood changes — symptoms that overlap with estradiol-related issues. In rare cases, significantly elevated prolactin can indicate a pituitary prolactinoma. A baseline prolactin before starting TRT helps rule out this as a cause of hypogonadism. On TRT, prolactin should remain stable[12].

LH and FSH

Luteinizing hormone (LH) and follicle-stimulating hormone (FSH) will be suppressed to near-zero on TRT. This is expected — exogenous testosterone provides negative feedback to the hypothalamus and pituitary, shutting down endogenous production. This is why TRT causes testicular atrophy and impairs fertility. Checking LH/FSH on TRT confirms the feedback loop is working as expected; they are more useful as a diagnostic tool before starting TRT to differentiate primary from secondary hypogonadism[2].

When to test: timing relative to your injection

Injection timing significantly affects blood testosterone levels. For testosterone cypionate or enanthate (the most common injectable forms), the pharmacokinetic profile looks roughly like this:

• Peak: 24-48 hours after injection
• Trough: The day of the next injection (before injecting)

The clinical standard is to draw blood at the trough — the morning of your next scheduled injection, before you inject. This gives the most clinically meaningful reading because it captures your lowest testosterone level. If your trough is in the target range, your levels are adequate throughout the entire dosing interval[2].

Drawing blood at the peak (24-48 hours post-injection) can produce misleadingly high values and doesn't tell you whether your levels drop too low before the next dose.

Dose adjustment signals from blood work

Blood work should drive protocol adjustments. Here are the common scenarios:

Monitoring schedule

• Baseline (before starting TRT): Total testosterone (two morning measurements), free testosterone, SHBG, estradiol (sensitive), LH, FSH, prolactin, CBC (hematocrit/hemoglobin), PSA, lipid panel, liver enzymes, metabolic panel
• 6-8 weeks after starting or changing dose: Total and free testosterone (at trough), hematocrit, estradiol (sensitive). This is your early safety and dose-calibration check.
• 3 months: Full panel including all markers above. This confirms dose adequacy and flags emerging issues.
• 6 months: Full panel repeat. By now, hematocrit should have reached its new equilibrium.
• Every 6-12 months (ongoing): Full panel. PSA annually at minimum. Lipids every 6-12 months[13].

Red flags that require immediate action

• Hematocrit above 54% — withhold TRT, phlebotomy, recheck in 4 weeks[2]
• PSA above 4.0 ng/mL or velocity above 0.75 ng/mL/year — urological evaluation
• Severe polycythemia symptoms (headache, visual disturbance, dizziness, skin redness) — urgent medical evaluation
• Signs of DVT or PE (leg swelling, chest pain, shortness of breath) — emergency evaluation
• Prolactin significantly elevated (above 2x ULN) — pituitary imaging
• Liver enzymes above 3x ULN — investigate cause (less likely from injectable TRT itself)