Safe, effective testosterone replacement therapy requires regular blood monitoring. This guide explains exactly which tests are needed, how often, and what the numbers should look like.
June 2026 · 9 min read · Lambert Medical Clinical Team
TRT is not a prescription you fill once and forget. Done properly, it involves a structured monitoring programme that adjusts dose based on blood levels, watches for safety parameters like haematocrit and PSA, and ensures your body is responding as expected. Understanding what your GP is checking — and why — makes you a more informed patient and helps you spot when something needs attention.
Essential before first dose
A full baseline is mandatory before starting any testosterone therapy. This establishes your pre-treatment levels for comparison, rules out contraindications, and identifies any pre-existing issues that TRT might worsen.
After starting or changing dose
The 6-week check is primarily about dose assessment and safety. It tells you whether testosterone has reached therapeutic range, whether haematocrit is rising, and whether oestradiol conversion is excessive. The timing of blood draw matters — see the section below on when to test.
First comprehensive panel
By 3 months, testosterone levels have stabilised on most delivery methods. This is the first opportunity for a meaningful full assessment of response — symptom improvement, hormone levels, and metabolic effects.
When dose is stable and response is consistent
Once you are on a stable dose with consistent results, 6-monthly monitoring is standard. Some guidelines allow annual monitoring for very stable patients with no concerning trends — but haematocrit should be checked at least every 6 months.
The timing of a testosterone blood draw relative to your last dose significantly affects the result. Drawing at the wrong time produces a misleading level that can lead to unnecessary dose changes. Here is the correct timing for each delivery method:
| Delivery Method | When to Test | What You're Measuring |
|---|---|---|
| Testosterone gel (daily) | Before applying your daily dose (trough level) | Trough — the lowest point in your 24-hour cycle |
| Testogel / Tostran | As above — before morning application | Consistent trough comparison |
| Testosterone enanthate (weekly) | Mid-cycle — 3–4 days after injection | Peak-to-trough midpoint |
| Testosterone enanthate (fortnightly) | Trough — just before next injection (day 13–14) | Trough level — avoids overestimating steady state |
| Nebido (every 10–14 weeks) | Trough — 1–2 weeks before next injection | Trough — determines if interval is appropriate |
| Testosterone pellets / implants | 6–8 weeks after insertion | Steady-state level |
Men on weekly enanthate injections who test 24–48 hours after their dose will show supraphysiological testosterone levels that look alarming — and may lead to unnecessary dose reductions. Similarly, testing at trough (just before next injection) on weekly dosing will show an artificially low level. The goal is a mid-cycle draw that represents a meaningful average. Always tell your GP or phlebotomist when your last dose was.
There is no single "correct" testosterone level on TRT — the target is the level at which your symptoms resolve and you feel well, within a physiologically normal range. UK guidelines generally aim for mid-normal range: approximately 15–25 nmol/L for total testosterone (trough measurement).
Free testosterone is often more clinically relevant than total testosterone — it represents the biologically active fraction. Men with low SHBG (common with obesity, insulin resistance, or hypothyroidism) may have adequate total testosterone but low free testosterone. Men with high SHBG (common with age) may have borderline total testosterone but normal free levels. Both need to be assessed together.
Testosterone stimulates erythropoiesis — the production of red blood cells — by increasing erythropoietin secretion from the kidneys. In some men, this causes haematocrit to rise above normal levels (above 48–50%), a condition called secondary erythrocytosis.
Why does this matter? Elevated haematocrit thickens the blood, increasing viscosity and raising the risk of cardiovascular events — heart attack, stroke, deep vein thrombosis. The higher the haematocrit, the greater the risk.
| Haematocrit | Interpretation | Action |
|---|---|---|
| < 50% | Normal range | Continue — recheck at next scheduled review |
| 50–54% | Elevated — monitor closely | Ensure adequate hydration; consider dose reduction; recheck in 6–8 weeks |
| > 54% | Action required | Pause or reduce TRT; consider therapeutic venesection (blood donation); investigate for secondary causes |
Men most at risk of elevated haematocrit are those on injections (which cause larger peaks in testosterone), those at altitude, smokers, and those with sleep apnoea (which independently raises haematocrit). If you snore heavily or have disrupted sleep on TRT, sleep apnoea screening is worthwhile.
PSA (prostate-specific antigen) is a protein produced by the prostate gland. Elevated or rising PSA can indicate benign prostatic hyperplasia, prostatitis, or prostate cancer. Testosterone does not cause prostate cancer, but it can stimulate growth of an existing undetected cancer — which is why a baseline PSA before TRT and regular monitoring thereafter is essential.
| PSA Change | Action |
|---|---|
| Rise < 1.4 ng/mL over 12 months | Normal variation — continue monitoring |
| Rise > 1.4 ng/mL in 12 months | Pause TRT; urology referral |
| PSA > 4.0 ng/mL (any age) | Urology referral; pause TRT pending investigation |
| PSA > 3.0 ng/mL in high-risk patients | Discuss with urology |
Testosterone naturally converts to oestradiol through aromatase enzymes, particularly in adipose (fat) tissue. On TRT, some men produce excess oestradiol, leading to symptoms including breast tenderness or enlargement (gynaecomastia), water retention, mood changes, and reduced libido — paradoxically similar to low testosterone symptoms.
Target oestradiol on TRT is typically 100–200 pmol/L (or 30–60 pg/mL). Levels above this range may warrant a dose reduction, a switch to a lower-peak delivery method, or in some cases an aromatase inhibitor — though aromatase inhibitors should be used cautiously and are not appropriate for most men on TRT.
Men with higher body fat aromatise more testosterone to oestradiol. Reducing body fat through diet and exercise is the most effective long-term approach to managing oestradiol on TRT.
We provide structured TRT blood monitoring for men on testosterone therapy — whether prescribed by us or elsewhere. Our panel covers testosterone (total and free), haematocrit, PSA, oestradiol, LH/FSH, SHBG, LFTs, and metabolic markers, with GP review of results.
Structured monitoring panel with GP review — suitable for men on TRT from any provider.
Book NowHaematocrit >54%
Pause TRT — contact your GP
PSA rise >1.4 in 12 months
Urology referral required
Oestradiol >200 pmol/L
Review dose / delivery method