- 01The testosterone number is about timing; the safety numbers are hematocrit and PSA
On injections, testosterone can swing by hundreds of ng/dL across one week on the same dose, so a result only means something next to the day it was drawn. Whether treatment needs to pause or be reviewed is decided by hematocrit and PSA, read against your own pre-TRT baseline, and that decision is your prescriber's.
TRT blood work checks three things that matter: testosterone, to see where the dose lands; hematocrit, the share of your blood made of red cells; and PSA, a prostate marker. On testosterone replacement therapy (TRT), the testosterone number depends heavily on when the blood was drawn. A man on weekly injections can read about 1,000 ng/dL two days after a shot and 450 ng/dL the morning before the next one, on the same dose. Hematocrit creeps up over the first year, and you cannot feel it rising.
Before you start: baseline labs for TRT
The Endocrine Society diagnoses low testosterone (hypogonadism) only when symptoms come with a total testosterone below the range on at least two separate early-morning fasting samples 1. New to the diagnosis itself? Start with low testosterone. One low result is not enough, because testosterone runs highest in the morning and drops after a poor night, an illness or a big meal. The rest of the baseline panel looks for a cause and records your starting point, so later results have something to be compared against.
| Marker | Why it is checked before TRT | What it tells you later |
|---|---|---|
| Total testosterone (x2, morning, fasting) | Confirms the diagnosis 1 | Your untreated starting level |
| LH and FSH | High means the testes are the problem; low or normal points to the pituitary | On TRT both fall near zero, which is expected |
| SHBG and calculated free testosterone | Shows how much testosterone is available when total is borderline | Explains why two men with the same total feel different |
| Prolactin | Checked when LH is low, to rule out a pituitary cause | Rarely needed again |
| CBC: hematocrit and hemoglobin | The Endocrine Society and the AUA advise against starting TRT with an already raised hematocrit; the AUA's line is 50% 1 2 | The number most likely to move on TRT |
| PSA | Prostate baseline for men 55 to 69, and from 40 for men at higher risk 1 | The yardstick for the 1.4 ng/mL rule |
| Lipids, liver enzymes, HbA1c, creatinine | Records your metabolic and kidney starting point | Lets you judge later shifts against your own numbers |
Markers to read beside your baseline testosterone
What gets checked once you are on TRT, and why
Follow-up panels are shorter than the baseline. Each marker below has one job on TRT.
- Total testosterone blood test: is the dose landing mid-range at the agreed point in your cycle?
- Free testosterone blood test and SHBG: context when total testosterone and symptoms do not match. See the male hormone panel guide.
- Hematocrit and hemoglobin: the main safety check, because testosterone pushes red cell production up. The CBC guide explains the rest of the count.
- PSA: a small rise in the first year is expected, then it should level off.
- Estradiol: worth measuring when you have breast tenderness or swelling, not as a routine target 2.
- Lipids and liver enzymes: HDL can dip a little; liver enzymes rarely move on injections or gels.
- Creatinine: often nudges up as muscle mass grows, which can make eGFR (the kidney-function estimate calculated from creatinine) look lower than kidney function is; ask your prescriber before assuming that is the reason.
- LH and FSH: near zero on TRT. A near-zero LH means the therapy is doing what it does, and it explains the fertility effect.
How often: the monitoring schedule
The Endocrine Society advises a review 3 to 12 months after starting and then yearly, with hematocrit checked at baseline, at 3 to 6 months, at 12 months and then every year 1. The AUA suggests measuring testosterone every 6 to 12 months once you are settled, with hematocrit and PSA rechecked periodically 2. Red cell production rises most during the first year, so that year carries most of the risk of a high hematocrit.
| When | What is usually checked | Why |
|---|---|---|
| Baseline | Full panel above | Diagnosis and your own reference point |
| 3 to 6 months | Testosterone, hematocrit, PSA (if checked at baseline, or at your prescriber's call), symptoms | Is the dose in range; early red cell rise 1 |
| 12 months | Testosterone, hematocrit, PSA, lipids | Red cells and PSA usually settle around now |
| Every year after | Testosterone, hematocrit, PSA | Catches slow drift against your own baseline |
| After any change of dose or form | Testosterone, hematocrit | A new dose or form needs a fresh read, at a time your prescriber sets |
When to draw blood: timing by type of TRT
Injected testosterone climbs to a peak within two to three days of a shot, then falls until the next one. A draw on day two and a draw on day six of the same weekly cycle can differ by hundreds of ng/dL without any change in dose, so the timing decides what your number means.
| Type of TRT | When to test | What the number represents |
|---|---|---|
| Testosterone cypionate or enanthate injections (weekly or every 2 weeks) | Midway between injections 1; some prescribers prefer a trough just before the next shot | An average day (midway) or your lowest point (trough) |
| Sustanon 250 (mixed esters, often every 3 weeks in the UK) | Many UK clinics test just before the next injection; agree the point with your prescriber | Your trough, the lowest level |
| Testosterone gel (e.g. Testogel, Tostran) | 2 to 8 hours after applying, after at least a week on the dose 1 | Your usual daily level. Do not draw from the arm the gel went on. |
| Testosterone patch | 3 to 12 hours after applying 1 | Your daytime level |
| Testosterone undecanoate injection (Aveed in the US, Nebido in the UK) | At the end of the interval, just before the next injection 1 | Your trough, the lowest level |
| Pellets | At the end of the dosing interval, before re-implanting 1 | Whether the pellets last the full interval |
Reading your numbers: the ranges that matter on TRT
US labs report testosterone in ng/dL and UK labs in nmol/L; 1 nmol/L equals 28.84 ng/dL. The harmonized reference range (one range agreed across several large studies, so labs can be compared) for healthy, non-obese men aged 19 to 39 is 264 to 916 ng/dL 3. Guidelines aim for the middle of a range like that on treatment, not the top.
| Reading | ng/dL (US) | nmol/L (UK) |
|---|---|---|
| Harmonized reference range, men 19 to 39 3 | 264 to 916 | 9.2 to 31.8 |
| AUA target on TRT 2 | 450 to 600 | 15.6 to 20.8 |
| Above the harmonized upper limit 3 | above 916 | above 31.8 |
CalculatorTestosterone converterYour lab reports in the other unit? Convert ng/dL and nmol/L in one step.Work it out A trough of 350 ng/dL (12.1 nmol/L) and a midway result of 900 ng/dL (31.2 nmol/L) can come from the same dose. Read each against the point in the cycle it was drawn. A result well above the target range at your agreed draw point is a reason to talk to your prescriber (see high testosterone); a trough under the range is a reason to ask about the interval. If your total testosterone and your symptoms disagree, free testosterone, calculated from total testosterone and SHBG, often explains the gap.
CalculatorFree testosterone calculatorPut your total testosterone and SHBG in to see how much is free.Work it out High hematocrit on TRT
Testosterone raises EPO (erythropoietin, the kidney hormone that tells bone marrow to make red cells) and lowers hepcidin, the hormone that locks iron away, so the marrow has both the signal and the iron to make more red cells. That is why hematocrit is the line to watch on a TRT report. The rise is larger on short-acting injections and higher doses, and in older men 1; smoking, untreated sleep apnea and living at altitude can add to it. The Endocrine Society advises pausing therapy when hematocrit goes above 54% until it falls to a safe level, then restarting at a lower dose 1. That is your prescriber's call: do not stop or change your dose on your own. If your result is above 54%, call your prescriber before your next dose rather than waiting for the next scheduled check. Prescribers may also switch you to a gel, look for sleep apnea, or arrange blood donation in some cases.
Example hematocrit on TRT%
TRAVERSE followed 5,246 men aged 45 to 80 with low testosterone and high heart risk. Major heart events were similar on testosterone gel and placebo (7.0% vs 7.3%), while atrial fibrillation (an irregular heartbeat), acute kidney injury and pulmonary embolism were more frequent on testosterone 4.
In men with hypogonadism and preexisting or a high risk of cardiovascular disease, testosterone-replacement therapy was noninferior to placebo with respect to the incidence of major adverse cardiac events.Lincoff AM et al., TRAVERSE, New England Journal of Medicine 2023 4
In plain words: heart attacks, strokes and heart deaths were no more common on testosterone than on a dummy gel.
Read alongside hematocrit
A high red cell count on TRT has a known cause outside the marrow. Polycythemia vera is different: the bone marrow makes too many red cells on its own. For how the two are told apart, see high RBC and polycythemia vera.
Estradiol on TRT: when the number matters
Some testosterone converts to estradiol through an enzyme called aromatase, so estradiol rises with the dose. The AUA advises measuring estradiol in men with breast tenderness or breast swelling (gynecomastia), rather than in everyone 2. The test itself is a problem at male levels: the Endocrine Society's position statement found the standard estradiol test (an immunoassay, the common antibody-based method) inaccurate at men's low levels, and recommends a more precise method called mass spectrometry (LC-MS/MS) 5.
Driving estradiol down to hit a number is not part of guideline care. Do not start or stop an estradiol-lowering medicine without your prescriber. In men, estradiol supports libido and sexual function and helps limit body fat gain 8, and low estradiol brings its own problems. For what a raised result can mean, see high estradiol.
PSA on TRT: a small rise is expected
PSA usually rises a little in the first months of TRT and levels off by about 12 months; compare it to your pre-TRT baseline, because the change matters more than a single value. The Endocrine Society advises a urology review if PSA rises more than 1.4 ng/mL within 12 months of starting, if a confirmed PSA is above 4.0 ng/mL, or if the prostate exam is abnormal 1. Your prescriber arranges that referral. In the TRAVERSE prostate analysis, high-grade prostate cancer was uncommon (under 0.2% in each group) and the rate did not differ significantly between testosterone and placebo 6.
For how PSA sits among other tumor markers and why one result rarely settles anything, see tumor markers explained.
Lipids, liver, kidneys and blood sugar
HDL cholesterol can dip modestly on TRT; read it against your baseline and the lipid panel guide, see low HDL if it falls below range, and check your total-to-HDL ratio with the cholesterol ratio calculator. Liver enzymes rarely move on injected or skin-applied testosterone. Creatinine often rises as muscle mass grows, which can lower the calculated eGFR without kidney damage. A falling eGFR is still worth raising with your prescriber, who can check it another way, such as with a cystatin C test, which muscle does not affect; see cystatin C vs creatinine. HbA1c may improve in men who lose fat on treatment.
Why your results jump around
- Cycle timing: day two and day six of a weekly injection cycle can differ by several hundred ng/dL.
- Time of day and sleep: draw in the morning after a normal night.
- Assay type: immunoassays and LC-MS/MS (mass spectrometry) give different numbers, especially for estradiol 5.
- Capillary versus venous: a finger-prick sample can read differently from an arm draw; see are at-home blood tests accurate.
- Lab ranges: each lab sets its own range, so a flag at one lab may not appear at another.
- Upper reporting limits: a very high result may be reported as ">1,500" or ">2,000" ng/dL, which means above what the assay counts, not an exact value.
- Missing free testosterone: if total testosterone is above the assay's upper limit, or SHBG was not run, the lab cannot calculate free testosterone and leaves it blank.
- Illness and hydration: a recent infection or a dehydrated morning can shift testosterone and hematocrit.
Three results drawn the same way, at the same lab and the same point in your cycle, show a real change; one result cannot.
Your baseline panel, the same lab and the same point in your cycle turn these swings into a readable line. Bring that line to your prescriber, with the dates of any dose or form change marked on it.
Free, no accountRead your blood testLine up your TRT results against your baseline and the guideline thresholds before your next appointment.Read my results
Citations
- Bhasin S et al. Testosterone Therapy in Men With Hypogonadism: An Endocrine Society Clinical Practice Guideline. J Clin Endocrinol Metab 2018;103(5):1715-1744
- Mulhall JP et al. Evaluation and Management of Testosterone Deficiency: AUA Guideline. J Urol 2018;200(2):423-432
- Travison TG et al. Harmonized Reference Ranges for Circulating Testosterone Levels in Men of Four Cohort Studies in the United States and Europe. J Clin Endocrinol Metab 2017;102(4):1161-1173
- Lincoff AM et al. Cardiovascular Safety of Testosterone-Replacement Therapy (TRAVERSE). N Engl J Med 2023;389:107-117
- Rosner W et al. Challenges to the Measurement of Estradiol: An Endocrine Society Position Statement. J Clin Endocrinol Metab 2013;98(4):1376-1387
- Bhasin S et al. Prostate Safety Events During Testosterone Replacement Therapy in Men With Hypogonadism: A Randomized Clinical Trial. JAMA Netw Open 2023;6(12):e2348692
- World Health Organization Task Force on Methods for the Regulation of Male Fertility. Contraceptive efficacy of testosterone-induced azoospermia in normal men. Lancet 1990;336(8721):955-959
- Finkelstein JS et al. Gonadal Steroids and Body Composition, Strength, and Sexual Function in Men. N Engl J Med 2013;369:1011-1022
Educational context only, not medical advice or a diagnosis. Always discuss your results with a clinician.
