Lab Cheat Sheet: What TT, FT, SHBG, and E2 Actually Mean

If you're on TRT, you need to track four key markers. Here's what each one means, what range you want, and when to worry.

Total Testosterone (TT)

What it measures: All the testosterone in your blood—both bound to proteins and free.

Optimal range: 600-900 ng/dL

Red flags:

• Below 500: Likely underdosed or absorption issue
• Above 1000 consistently: May be on too high a dose

Context: TT alone doesn't tell the full story. You can have high total T but low free T if SHBG is high.

Free Testosterone (FT)

What it measures: The unbound, biologically active testosterone your body can actually use.

Optimal range: 15-25 ng/dL (or 150-250 pg/mL)

Red flags:

• Below 10: You'll likely have low-T symptoms regardless of total T
• Below 15 with high total T: Check SHBG—it's probably elevated

Why it matters: FT drives symptoms more than TT. Two men can have the same total T but very different free T.

SHBG (Sex Hormone Binding Globulin)

What it measures: The protein that binds to testosterone and makes it unavailable.

Optimal range: 20-40 nmol/L

Red flags:

• Above 50: Binding up too much testosterone, lowering free T
• Below 15: Often indicates insulin resistance; can cause rapid T clearance

What affects it: High SHBG comes from aging, low carb diets, thyroid meds. Low SHBG comes from insulin resistance, obesity, high androgens.

Estradiol (E2)

What it measures: Your primary estrogen level. Men need some E2 for bone health, libido, and mood.

Optimal range: 20-30 pg/mL (using sensitive LC/MS assay)

Red flags:

• Below 20: Joint pain, low libido, mood issues
• Above 40: Water retention, emotional sensitivity, gynecomastia risk

Important: Use the sensitive assay (LC/MS), not standard estradiol test. Standard tests overestimate in men.

How These Four Work Together

Think of it like this:

• Total T = Raw material
• SHBG = Storage (binds T, keeps it from being used)
• Free T = Active ingredient (what actually works)
• E2 = Byproduct that needs balance (too little or too much causes problems)

Quick Reference Table

When to Test

• Baseline: Before starting TRT
• 6 weeks: After starting or changing dose
• Every 3-6 months: Once stable
• Trough levels: Test right before your next injection (not peak)

Want the full breakdown? Read the complete guide to reading TRT labs with common traps and what to do next.

References

1. 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
2. Brand JS, van der Tweel I, Grobbee DE, et al. Testosterone, SHBG and the metabolic syndrome: a systematic review and meta-analysis. Int J Epidemiol. 2011;40(1):189-207. Link
3. 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
4. Vermeulen A, Verdonck L, Kaufman JM. A critical evaluation of simple methods for the estimation of free testosterone in serum. J Clin Endocrinol Metab. 1999;84(10):3666-3672. Link
5. Kupelian V, Page ST, Araujo AB, et al. Sex Hormone-Binding Globulin, but Not Testosterone, Is Associated Prospectively and Independently With Incident Metabolic Syndrome in Men. Diabetes Care. 2010;33(7):1618-1624. Link