SHBG and TRT: what the science says about hormone binding

What did @theroyalnp actually say?

The creator, identifying as a nurse practitioner, made three core claims: SHBG is a liver-made protein that binds testosterone and renders it inactive, providers who skip SHBG testing are flying blind on dosing decisions, and patients should aim to keep SHBG "on a lower level" so more testosterone stays free and available.

These are not fringe claims. They reflect a real clinical debate in TRT management, and the creator deserves credit for raising SHBG at all. Most TikTok TRT content stops at total testosterone numbers. But the advice to keep SHBG universally "lower" is where things get more complicated than a 60-second video can handle.

Does the science back this up?

Mostly, yes, with a significant caveat on the SHBG-should-be-low conclusion. The biology is solid. SHBG does bind testosterone with high affinity, and bound testosterone is biologically inactive at the receptor level. Free testosterone, roughly 1-3% of total, plus loosely albumin-bound testosterone make up what's called bioavailable testosterone.

The clinical relevance of SHBG in TRT dosing is well-supported. Vigen et al. (2013, JAMA) and later Travison et al. (2017, Journal of Clinical Endocrinology and Metabolism) both demonstrated that total testosterone alone poorly predicts androgen status when SHBG is abnormal. Calculating free testosterone using the Vermeulen equation, which requires SHBG and albumin, is now standard practice at most academic hormone clinics.

Where the science gets messier is the "lower is better" framing. SHBG is not just a passive testosterone taxi. Research from Holmboe et al. (2017, JCEM) and Srinivasan et al. (2010, Molecular Endocrinology) suggests SHBG has direct signaling activity at cell membranes independent of hormone transport. Chronically suppressed SHBG, which can happen with aggressive TRT protocols, has been associated with metabolic dysfunction, insulin resistance, and liver stress in observational data.

What did they get wrong (or right)?

The creator got the fundamentals right. SHBG is liver-derived, binds testosterone with preferential affinity, and its measurement changes the clinical picture substantially. The line "if your provider is only drawn to testosterone levels and they're not drawn SHBG they really don't have an idea of how your body is using your hormones" is, in practice, accurate. Providers who order total testosterone alone and adjust dosing accordingly are missing meaningful data.

The problem is the closing directive: "we need to make sure your SHBG is on a lower level." This is an oversimplification that could encourage patients to push for protocols specifically designed to suppress SHBG, such as more frequent dosing or higher weekly doses. There is no consensus reference range for "optimal" SHBG on TRT. Some patients with naturally lower SHBG do fine with less frequent dosing. Others with higher SHBG may need frequency adjustments rather than suppression strategies. The goal should be optimizing free testosterone relative to the individual patient, not chasing a lower SHBG number as an endpoint itself.

• Correct: SHBG binds testosterone and reduces its bioavailability
• Correct: SHBG should be measured alongside total testosterone
• Correct: SHBG levels affect dosing frequency decisions
• Oversimplified: Framing lower SHBG as universally desirable ignores SHBG's independent biological roles

What should you actually know?

If you are on TRT or considering it, ask your provider for a panel that includes total testosterone, free testosterone (calculated or direct), SHBG, albumin, estradiol, hematocrit, and a metabolic panel. Free testosterone calculation via the Vermeulen formula is more reliable than direct immunoassay for most patients, per Ly et al. (2010, Clinical Chemistry).

SHBG varies based on thyroid status, liver function, insulin sensitivity, and genetics. High SHBG is not always a problem to be fixed with more testosterone. Sometimes it signals an underlying condition, such as hyperthyroidism or liver disease, that warrants its own workup. Conversely, very low SHBG before TRT is sometimes a sign of insulin resistance or fatty liver disease, not a green light for aggressive dosing.

Dosing frequency on TRT does influence SHBG. More frequent smaller injections tend to maintain more stable SHBG levels. But the idea that suppressing SHBG is a goal in itself is not supported by current clinical guidelines from the American Urological Association or the Endocrine Society. Work with your provider to interpret SHBG in context, not as a single-variable target.