Free Testosterone vs Total Testosterone: What to Track on TRT
Matt · May 8, 2026
Total testosterone measures every testosterone molecule in your bloodstream, but most of it is bound to proteins and unavailable to your tissues. Free testosterone is the unbound fraction — typically 1–3% of the total — and it's the portion that actually interacts with androgen receptors. On TRT, many users report that free T tracks closer to their symptoms than total T does.
Why the difference matters
Roughly 60–70% of testosterone is bound tightly to sex hormone-binding globulin (SHBG), and another 25–30% is loosely bound to albumin. Only the small unbound fraction is "free" to enter cells. If your SHBG is high, you can have a perfectly normal total testosterone level and still feel low because very little is bioavailable.
This is why two people with identical total T numbers can feel completely different. One person with SHBG of 25 nmol/L will have a much higher free T than someone with SHBG of 70 nmol/L, even at the same total. Research suggests free testosterone may be a better predictor of symptoms like fatigue, low libido, and brain fog than total testosterone alone.
What to actually track
A useful TRT bloodwork panel typically includes:
- Total testosterone — the headline number, but incomplete on its own
- Free testosterone — ideally measured by equilibrium dialysis (the gold standard) rather than calculated
- SHBG — explains why your free T is high or low
- Albumin — used in calculated free T formulas
- Estradiol (sensitive assay) — rises with higher testosterone levels
- Hematocrit — for blood thickness monitoring
Many labs report a "calculated free testosterone" using the Vermeulen formula, which uses total T, SHBG, and albumin. This is generally accurate but can drift at extreme SHBG values. Direct measurement is more reliable if your numbers don't match how you feel.
Logging trends, not single data points
A single blood draw is a snapshot. What matters more is the trend across multiple labs at consistent timing — same time of day, same point in your injection cycle, same fasting status. Trace lets you log each lab result alongside your dose, injection timing, and how you're feeling that week, so patterns become visible over months instead of getting lost between appointments. Everything stays on your device, protected by Face ID.
Talk to your doctor before adjusting protocol based on lab numbers — context matters, and what looks "off" on paper may be perfectly fine for your situation.
Frequently Asked Questions
Should I optimize for free T or total T on TRT?
Most clinicians look at both, but symptoms and free T tend to correlate more closely. If your total T is mid-range but free T is low, your dose or SHBG may need attention. Always discuss interpretation with your prescribing doctor.
Why is my SHBG so high (or low)?
SHBG is influenced by genetics, thyroid function, liver health, insulin sensitivity, and body composition. Higher SHBG generally means lower free T at any given total T. Low SHBG can indicate insulin resistance or fatty liver in some cases.
When should I draw blood relative to my injection?
For weekly injections, trough levels (right before next injection) are most common. For more frequent protocols like daily or EOD, timing matters less because levels are more stable. Keep your timing consistent across labs so you're comparing apples to apples.