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.
The Markers That Actually Matter
These are the six markers you need to track on TRT:
- Total Testosterone (TT) — The raw amount in your blood
- Free Testosterone (FT) — The active, usable testosterone
- SHBG — The protein that binds testosterone
- Estradiol (E2) — The primary estrogen men produce
- Hematocrit/Hemoglobin — Blood thickness markers
- Lipids — Cardiovascular risk indicators
Let's break each down.
Total Testosterone (TT)
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).
Optimal Range
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.
Common Traps
- Chasing high numbers: More isn't always better. Some men feel great at 600, others need 900. Symptoms matter more than numbers.
- Testing at the wrong time: If you inject weekly, test at trough (right before your next injection) to see your lowest point—not peak.
- Ignoring SHBG: High total testosterone with high SHBG can still mean low free testosterone (the active form).
What to Do Next
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 (FT)
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.
Optimal Range
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.
Common Traps
- Not testing it: Some doctors only test total testosterone. This misses the whole picture—high TT with low FT is common.
- Using direct vs. calculated: Direct free T assays are less accurate. Calculated free T (using TT, SHBG, and albumin) is more reliable.
- Ignoring symptoms: Some men have "normal" free T but still feel off. Androgen receptor sensitivity varies.
What to Do Next
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 (Sex Hormone Binding Globulin)
SHBG is a protein that binds to testosterone and makes it unavailable. High SHBG means less free testosterone—even if your total is good.
Optimal Range
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.
What Affects SHBG
Increases SHBG:
- Aging
- Low insulin/low carb diets (chronic)
- Thyroid medication
- Estrogen
- Liver disease
Decreases SHBG:
- Insulin resistance / high insulin
- Obesity
- High androgen levels
- Hypothyroidism
- Certain medications (stanozolol, danazol)
What to Do Next
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.
Estradiol (E2)
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.
Optimal Range
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.
What to Do Next
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.
Hematocrit and Hemoglobin
TRT stimulates erythropoiesis (red blood cell production). More RBCs can improve oxygen delivery—but too many thicken your blood, increasing cardiovascular risk.
Optimal Range
Hemoglobin: 15-16.5 g/dL
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%.
What to Do Next
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.
Lipids
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.
What to Watch
- LDL: Keep below 130 mg/dL (ideally below 100)
- HDL: Keep above 40 mg/dL
- Triglycerides: Keep below 150 mg/dL
What to Do Next
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.
Putting It All Together
Here's how to interpret your labs as a complete picture:
Scenario 1: "I feel great"
- TT: 750 ng/dL
- FT: 18 ng/dL
- SHBG: 30 nmol/L
- E2: 28 pg/mL
- Hematocrit: 48%
Verdict: Dialed in. Don't change anything.
Scenario 2: "I still have low T symptoms"
- TT: 850 ng/dL
- FT: 8 ng/dL
- SHBG: 65 nmol/L
- E2: 22 pg/mL
Verdict: High SHBG is binding up your testosterone. Address insulin sensitivity and thyroid.
Scenario 3: "I'm moody and bloated"
- TT: 600 ng/dL
- FT: 20 ng/dL
- SHBG: 18 nmol/L
- E2: 55 pg/mL
Verdict: High estrogen. Lower body fat, consider more frequent injections, or discuss AI.
Lab Timing Matters
When you test is as important as what you test:
- Twice-weekly injections: Test at trough (right before injection) to see your lowest point
- Daily/every-other-day: Timing matters less—levels are stable
- Creams: Test 4-6 hours after application for peak levels
The Bottom Line
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.
References
- Bhasin S, Brito JP, Cunningham GR, et al. Testosterone Therapy in Men With Hypogonadism: An Endocrine Society Clinical Practice Guideline. J Clin Endocrinol Metab. 2018;103(5):1715-1744. Link
- Snyder PJ, Bhasin S, Cunningham GR, et al. Effects of Testosterone Treatment in Older Men. N Engl J Med. 2016;374(7):611-624. Link
- Brand JS, van der Tweel I, Grobbee DE, et al. Testosterone, SHBG and the metabolic syndrome: a systematic review and meta-analysis of observational studies. Int J Epidemiol. 2011;40(1):189-207. Link
- Cervi A, Balitsky AK. Testosterone therapy and secondary erythrocytosis. Can Urol Assoc J. 2022;16(5):E245-E248. Link
- Lincoff AM, Bhasin S, Flevaris P, et al. Cardiovascular Safety of Testosterone-Replacement Therapy. N Engl J Med. 2023;389(2):107-117. Link
- Khera M, Adaikan G, Buvat J, et al. Diagnosis and Treatment of Testosterone Deficiency: Recommendations from the Fourth International Consultation for Sexual Medicine (ICSM 2015). J Sex Med. 2016;13(12):1787-1804. Link
Related Guides
TRT Troubleshooting Checklist
When you feel worse on TRT—common problems and fixes for high E2, low SHBG, and hematocrit issues.
HCT/HGB on TRT: When to Worry
Managing hematocrit and hemoglobin on TRT—safe ranges, blood donation timing, and prevention.
Lab Cheat Sheet: TT, FT, SHBG, E2
Quick reference guide for the key markers every TRT patient should understand.
Master Your TRT Labs
Get the free TRT Lab Cheat Sheet—a quick reference for optimal ranges, red flags, and what to do next.
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