Total vs. free testosterone: what TikTok gets right and wrong

What did @ali_on_t actually say?

The creator walked through a fairly basic but genuinely useful distinction: total testosterone is everything circulating in your blood, while free testosterone is what's actually available for your body to use. They also dropped specific numbers, claiming the BSSM guidelines define low testosterone as total testosterone below 12.1 nmol/L or free testosterone below 0.225 nmol/L. And they called out GPs and the NHS for routinely skipping the free testosterone test.

That's three distinct claims in under a minute. It's more precise than most TRT content on TikTok, which usually stays in vague motivational territory. The creator is clearly familiar with the subject. The question is whether the specifics hold up.

Does the science back this up?

Mostly, yes. The total vs. free testosterone distinction is real, well-documented, and clinically relevant. Roughly 40-70% of circulating testosterone binds tightly to sex hormone-binding globulin (SHBG), making it biologically unavailable. Another 20-40% binds loosely to albumin. Only about 1-4% is genuinely free (Vermeulen et al., 1999, Journal of Clinical Endocrinology and Metabolism). So the creator's core point, that you can have normal total testosterone but functionally low free testosterone, is not just plausible, it's a documented clinical scenario.

On the BSSM thresholds, the British Society for Sexual Medicine guidelines do reference free testosterone cutoffs, and the 0.225 nmol/L figure for free testosterone appears in their published recommendations. The 12.1 nmol/L total testosterone threshold aligns with BSSM guidance as well, though it's worth noting these are not absolute diagnostic cutoffs but decision-support tools used alongside symptom assessment (BSSM Guidelines, 2017, Sexual Medicine).

What did they get wrong (or right)?

The creator mostly got this right. Credit where it's due. The total vs. free framework is accurate, and citing specific guideline thresholds rather than vague ranges is genuinely more useful than most of what circulates in this niche.

However, there are two things worth flagging. First, free testosterone measurement is notoriously unreliable when done by direct immunoassay, which is what most labs use. The gold standard is equilibrium dialysis, and calculated free testosterone using total testosterone, SHBG, and albumin is considered more accurate than a direct free T test in routine clinical practice (Ly et al., 2010, Clinical Biochemistry). So telling people to simply request a free testosterone test doesn't account for the fact that the test result itself may not be particularly trustworthy.

Second, presenting these thresholds as a clear diagnostic line glosses over the fact that hypogonadism diagnosis requires persistent symptoms alongside biochemical evidence. Numbers alone don't diagnose low testosterone (Bhasin et al., 2018, Journal of Clinical Endocrinology and Metabolism).

What should you actually know?

If you're investigating whether your testosterone levels are causing symptoms, testing both total and free testosterone is a reasonable starting point, and the creator is right that free testosterone often gets skipped. But the interpretation matters more than the number.

• Free testosterone measured by direct immunoassay is often inaccurate. Ask specifically whether your lab uses equilibrium dialysis or a calculated method based on SHBG and albumin. Calculated free T from a validated formula is generally preferred in clinical guidelines.
• The BSSM thresholds are decision aids, not binary on/off switches. A total testosterone of 11.9 nmol/L in an asymptomatic person is not the same clinical picture as someone at 11.9 nmol/L with fatigue, low libido, and poor mood.
• SHBG levels are the key variable that connects total testosterone to free testosterone. High SHBG, which can be driven by age, liver disease, hyperthyroidism, or certain medications, will suppress free testosterone even when total levels look fine (Rosner et al., 2007, Journal of Clinical Endocrinology and Metabolism).
• If you're pursuing a TRT evaluation, a responsible clinician should test total testosterone, SHBG, LH, FSH, and prolactin at minimum, not just total and free T in isolation.