If you're on testosterone replacement therapy (TRT), you need to understand your labs. Not just glance at them—actually understand what they mean, what optimal looks like, and what to do when something's off.
Most men get their labs drawn, see "normal" ranges, and assume everything's fine. But "normal" isn't the same as optimal. And more importantly, labs don't exist in isolation— you need to look at the full picture.
This guide breaks down every marker that matters for TRT: what it is, what optimal looks like, common interpretation traps, and exactly what to do next based on your results.
These are the six markers you need to track on TRT:
Let's break each down.
Total testosterone is exactly what it sounds like—the total amount of testosterone circulating in your blood. This includes both bound testosterone (attached to SHBG and albumin) and free testosterone (available for use).
Most labs show "normal" as 264-916 ng/dL. That's a massive range. A 30-year-old man at 270 ng/dL is "normal" but likely symptomatic. Meanwhile, 900 ng/dL is also "normal" and generally where men feel their best.
If your TT is below 600 at trough, discuss dose adjustments with your doctor. If it's above 1000 consistently, you might be on too high a dose. Symptoms should guide the decision more than the number.
Free testosterone is the unbound, biologically active testosterone your body can actually use. It's typically 2-3% of your total testosterone, but it's what drives symptoms.
Lab "normal" ranges vary widely here, often 9-30 ng/dL. But on TRT, 15-25 ng/dL is the sweet spot. Below 10 ng/dL, you'll likely have low-T symptoms regardless of your total testosterone.
If free T is low but total T is good, look at SHBG. High SHBG binds up your testosterone. Lowering SHBG (through diet, exercise, or medication changes) can help. In some cases, increasing total T dose raises free T sufficiently.
SHBG is a protein that binds to testosterone and makes it unavailable. High SHBG means less free testosterone—even if your total is good.
Labs often show 10-50 nmol/L as normal. But on TRT, you want SHBG in the 20-40 range. Above 50 nmol/L significantly reduces free testosterone. Below 15 nmol/L can cause excessive free T and estrogen conversion issues.
Increases SHBG:
Decreases SHBG:
If SHBG is high (above 50), address root causes first. Improve insulin sensitivity, optimize thyroid, and consider more frequent injections. If SHBG is very low (below 15), investigate metabolic health—this often signals insulin resistance.
Men produce estrogen too, primarily through aromatization (conversion of testosterone to estrogen). You need some estrogen for bone health, libido, and mood—but too much causes problems.
Standard lab ranges are 8-39 pg/mL. But on TRT, 20-30 pg/mL is the sweet spot. Below 20, you may have joint pain, low libido, and mood issues. Above 40, you may experience water retention, emotional sensitivity, and gynecomastia risk.
If E2 is elevated without symptoms, consider monitoring rather than treating. If you have symptoms (water retention, nipple sensitivity, emotional changes), options include: smaller, more frequent injections; reducing body fat; or in persistent cases, low-dose aromatase inhibitor.
TRT stimulates erythropoiesis (red blood cell production). More RBCs can improve oxygen delivery—but too many thicken your blood, increasing cardiovascular risk.
Labs show up to 54% as "normal," but on TRT you want to stay below 52%. Above 54% significantly increases risk. Many TRT doctors recommend therapeutic phlebotomy (blood donation) when hematocrit exceeds 52-54%.
If hematocrit is 50-52%, monitor closely and stay hydrated. If 52-54%, consider therapeutic phlebotomy (donate blood). If above 54%, discuss dose reduction with your doctor. More frequent injections (vs. large weekly doses) sometimes helps lower peak hematocrit.
TRT can affect your lipid profile. While some men see improvements (more muscle, less fat), others experience slight increases in LDL or decreases in HDL—especially at higher doses.
If lipids worsen on TRT, address diet first (reduce processed carbs, increase fiber and healthy fats). Consider cardarine or other interventions if significant issues persist. Some men need lower TRT doses for optimal lipids.
Here's how to interpret your labs as a complete picture:
Verdict: Dialed in. Don't change anything.
Verdict: High SHBG is binding up your testosterone. Address insulin sensitivity and thyroid.
Verdict: High estrogen. Lower body fat, consider more frequent injections, or discuss AI.
When you test is as important as what you test:
Reading TRT labs isn't about hitting perfect numbers—it's about finding the balance where you feel good and markers stay healthy. Track trends over time, not single readings. And remember: symptoms matter more than numbers. A man with TT of 600 who feels great is better off than a man with TT of 900 who feels terrible.
Work with a knowledgeable provider, test consistently, and adjust based on the full picture—not just one marker.
When you feel worse on TRT—common problems and fixes for high E2, low SHBG, and hematocrit issues.
Managing hematocrit and hemoglobin on TRT—safe ranges, blood donation timing, and prevention.
Quick reference guide for the key markers every TRT patient should understand.
Get the free TRT Lab Cheat Sheet—a quick reference for optimal ranges, red flags, and what to do next.