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TRT Before-and-After Blood Work: What to Test and When

Testosterone replacement therapy has a specific, guideline-published monitoring panel, not just a repeat testosterone level. Hematocrit is the safety marker that decides whether a dose continues at all. This page covers what to test before starting, when to retest, and how to read the result, not dosing, injection frequency, or where to source testosterone.

Medically reviewed · Guideline-anchored
Reviewed by Dr. Prahlad Rai Gupta, MBBS, MD · Thresholds anchored to the AUA and Endocrine Society testosterone-therapy guidelines · Evidence & Methodology
Anchored to AUA and Endocrine Society guidelines Covers testosterone, hematocrit, estradiol, PSA, and lipids What to test, not how to dose
Tracking testosterone outside a prescribed therapy?
Andrew Huberman is one of the longevity researchers who names testosterone as a marker in his own protocol, a different context from the clinical monitoring schedule above.
See Andrew Huberman's blood test markers

A baseline workup, then a safety-first retest schedule

Some markers here are diagnostic, checked once before starting to rule out other causes of low testosterone. Others are ongoing safety checks, rechecked on a set schedule for as long as therapy continues.

This page is part of FixFirst's Peptides & Hormones section. It covers the testing framework the American Urological Association (AUA) and the Endocrine Society publish for testosterone therapy: what to check before starting, what to recheck and on what schedule, and how to read the direction of change. It does not cover dose, injection frequency or delivery method, or where to obtain testosterone, questions for the prescribing physician managing the therapy.

Testosterone itself is the marker most people expect to retest, but it is not the one that determines whether therapy continues safely. That role belongs to hematocrit, the percentage of blood volume made up of red blood cells. Testosterone stimulates red blood cell production, and both AUA and Endocrine Society guidance name a hematocrit ceiling, generally cited around 54%, above which the increased blood viscosity raises clotting risk and the guidelines call for dose adjustment or discontinuation.

Testosterone is also relevant to longevity-focused tracking outside a prescribed therapy context. The Longevity blood markers section covers how Andrew Huberman frames testosterone as one of the hormone markers he tracks in his own protocol, a different, AI-curated context from the clinical monitoring schedule below.

What to test, and when

Three clusters. The first two run on an ongoing retest schedule for as long as therapy continues; the third is typically a one-time diagnostic workup before starting.

Cluster 1 of 3
Hormone response
The goal of therapy is bringing testosterone into a normal range while managing estradiol, the hormone testosterone partly converts into. Both are worth tracking, not just the total testosterone number.
Core Usually in a standard panel Ask Request specifically
Core
Total Testosterone
Guidelines generally point to rechecking around 3–6 months after starting or after a dose change, then periodically once stable, to confirm the level has moved into the target range the prescribing physician set.
Ask
Free Testosterone
Total testosterone includes hormone bound to carrier proteins and not biologically active; free testosterone (or an estimate calculated from total testosterone and SHBG) gives a more direct read on the hormone actually available to tissue.
Ask
Estradiol
Testosterone aromatizes into estradiol, and a rise here is expected on therapy. It's commonly checked alongside testosterone, particularly if symptoms like breast tenderness appear, though there's no single guideline-mandated target range across labs, since assay methods vary.
Cluster 2 of 3
Safety monitoring
These are the markers that determine whether therapy continues as prescribed, checked on their own schedule independent of how the hormone panel looks.
Core Usually in a standard panel Ask Request specifically
Core
Hematocrit / Hemoglobin
Checked at baseline, then again around 3–6 months, then periodically. AUA guidance names roughly 54% hematocrit as the threshold above which the guideline calls for dose reduction, discontinuation, or referral, since a rise raises blood-viscosity and clotting risk.
Core
PSA (Prostate-Specific Antigen)
For men over 40 or with prostate-cancer risk factors, checked at baseline and again within the first year, then per standard prostate-screening guidance. Endocrine Society guidance flags a PSA rise of roughly 1.4 ng/mL or more within 12 months, or a confirmed PSA above 4 ng/mL, as reasons for urology referral rather than continuing therapy unevaluated.
Cluster 3 of 3
Baseline diagnostic workup
These typically run once, before starting, to help identify why testosterone is low and rule out other causes, not as an ongoing retest on therapy.
Core Usually in a standard panel Ask Request specifically
Ask
LH & FSH
Luteinizing hormone and follicle-stimulating hormone help distinguish whether low testosterone originates in the testes (primary hypogonadism, LH/FSH typically elevated) or the pituitary/hypothalamus (secondary hypogonadism, LH/FSH typically low or inappropriately normal). Once on exogenous testosterone, LH and FSH are expected to drop as part of normal feedback suppression, so they're not a therapy-response marker to keep retesting.
Ask
SHBG (Sex Hormone-Binding Globulin)
Sex hormone-binding globulin carries most circulating testosterone and is used to calculate or estimate free testosterone. A baseline value helps interpret whether a total testosterone reading over- or understates the biologically active hormone level.
Ask
Lipid Panel
Not a guideline-mandated retest schedule specific to TRT, but a reasonable baseline given that low testosterone itself is associated with adverse metabolic risk, and a standard lipid panel is typically already part of routine care for the age group most often starting therapy.

Frequently asked questions

What blood tests are required before starting TRT?
A confirmed diagnosis of low testosterone typically requires two separate morning testosterone readings below the reference range, alongside a baseline hematocrit, PSA (for men over 40 or with risk factors), and LH/FSH to help identify the cause. Your prescribing physician determines the exact workup for your history.
How often should hematocrit be checked on TRT?
Guidelines generally call for a baseline check, a recheck around 3–6 months after starting or a dose change, then periodic monitoring for as long as therapy continues, more frequently if a reading is trending upward. A hematocrit around 54% or higher is the threshold both AUA and Endocrine Society guidance cite as a reason to adjust or pause therapy.
Does TRT raise PSA?
A modest PSA increase can occur early in therapy. Endocrine Society guidance treats a rise of roughly 1.4 ng/mL or more within 12 months, or a confirmed reading above 4 ng/mL, as a signal to refer to urology for further evaluation rather than something to monitor casually.
Why does estradiol matter on TRT if it's a testosterone therapy?
Testosterone partly converts into estradiol through a process called aromatization, so estradiol tends to rise alongside testosterone on therapy. It's commonly checked when symptoms like breast tenderness or water retention appear, though there's no single guideline-published target range, since lab assays differ.
Do LH and FSH matter once I'm already on TRT?
They're mainly a before-starting diagnostic to identify whether low testosterone originates in the testes or the pituitary. Once on exogenous testosterone, LH and FSH are expected to fall as part of normal hormonal feedback, so a low reading on therapy isn't itself a concern the way it would be before starting.

References & Guidelines

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