When a patient receives a testosterone result from a standard lab panel, they typically see one number: total testosterone. This number is useful. It is also incomplete. The clinical picture that determines whether hormone therapy is appropriate — and what the optimal dose looks like — requires a deeper look at what that number actually represents.
What total testosterone measures
Total testosterone is the sum of testosterone in all forms in the bloodstream: testosterone bound to sex hormone-binding globulin (SHBG), testosterone loosely bound to albumin, and testosterone that is entirely free and unbound. The measurement captures the full pool, regardless of which fraction is biologically accessible.
The vast majority of testosterone in circulation — roughly 97-99% — is bound. SHBG-bound testosterone is tightly held and largely unavailable to cells. Albumin-bound testosterone is more loosely held and can be released at the tissue level. Free testosterone, approximately 1-3% of the total, is immediately bioavailable and active at the androgen receptor.
Why only free testosterone matters at the receptor
Testosterone produces its effects by binding to intracellular androgen receptors, which then influence gene expression. Only testosterone that is free — unbound — can enter cells and bind those receptors directly. Tightly SHBG-bound testosterone cannot access the receptor.
This means that two patients with identical total testosterone values can have dramatically different physiological testosterone activity, depending on how much of that testosterone is free versus bound. A man with total testosterone of 500 ng/dL and very high SHBG may be functionally more testosterone-deficient than a man with total testosterone of 350 ng/dL and low SHBG.
This is not a theoretical distinction. It presents clinically — patients who have symptoms consistent with testosterone deficiency but a "normal" total testosterone are frequently found to have elevated SHBG driving low free testosterone.
What raises SHBG
Understanding what elevates SHBG is clinically relevant because SHBG levels are often modifiable or at least explainable:
Age. SHBG increases steadily with age in both men and women. This is one of the reasons men in their 50s and 60s can have total testosterone values that appear adequate while their free testosterone and clinical function have declined significantly.
Total testosterone is only half the picture.
A comprehensive hormone evaluation at Revitalize includes free testosterone and SHBG — the values that actually determine how much testosterone your body can use.
Book a ConsultationOral estrogen therapy. Oral estrogen — unlike transdermal or pellet delivery — significantly raises SHBG through hepatic first-pass effects. This is one clinical argument for non-oral estrogen delivery in hormone optimization.
Liver disease and hyperthyroidism. Both increase SHBG production.
Certain medications. Anticonvulsants and other medications affect SHBG levels.
Low insulin and very low body fat. SHBG is inversely related to insulin levels — low insulin states (including very lean body composition) can raise SHBG.
Calculated vs. direct free testosterone assays
Free testosterone can be measured in two ways: direct radioimmunoassay or calculated from total testosterone and SHBG using established formulas (the Vermeulen equation is the most widely used).
Both methods have limitations. Direct assays are often less accurate at lower testosterone ranges due to the difficulty of measuring such small fractions precisely. Calculated free testosterone, derived from total T and SHBG, is often more clinically reliable across the physiological range and is the preferred method in most hormone therapy practices.
A testosterone evaluation that includes only total testosterone misses the SHBG piece entirely. A comprehensive panel includes total testosterone, calculated or direct free testosterone, SHBG, LH and FSH (to distinguish primary from secondary hypogonadism), and estradiol.
The clinical implication
Testosterone optimization decisions at Revitalize are made on the basis of the complete hormonal picture — not a single total testosterone number. A patient with a total testosterone of 500 and free testosterone below the functional threshold is as much a clinical candidate for evaluation as a patient with a total testosterone of 250.
The goal of comprehensive evaluation is to understand what the patient's body is actually experiencing at the receptor level — which is what determines symptoms, function, and the appropriate clinical response.
Medical disclaimer: This article is for educational purposes only and does not constitute medical advice. Individual clinical decisions should be made in consultation with a qualified healthcare provider following appropriate evaluation. References to specific treatments, dosing, or protocols are informational.
Travis spent 17+ years in high-acuity clinical medicine — emergency, cardiac ICU, and cath lab — before founding Revitalize. He is a Certified Platinum Biote hormone therapy provider, the published author of You're Not Broken — You're Unbalanced, and the founder of the Rebuild Metabolic Health Institute. His clinical writing reflects the same precision he brought to critical care: specific, honest, and built around what actually works.