What this test measures
About 98% of circulating testosterone is bound — strongly to Sex Hormone Binding Globulin (SHBG, ~ 44%) and weakly to albumin (~ 54%). Only the unbound 2% (free testosterone) and the loosely albumin-bound fraction (together called "bioavailable testosterone") are biologically active.
Free testosterone matters most when SHBG is abnormal: obesity, type 2 diabetes, and chronic illness lower SHBG (so total testosterone looks falsely low even when free testosterone is normal); ageing, hyperthyroidism, oestrogen pills, and liver disease raise SHBG (so total testosterone looks falsely normal even when free testosterone is low).
The most reliable measurement is equilibrium dialysis-LC-MS/MS, but in routine Indian labs it is usually estimated using a calculated free testosterone from total T, SHBG and albumin — the formula recommended by the Endocrine Society.
Why it matters
In male hypogonadism, the Endocrine Society guideline recommends measuring free or bioavailable testosterone whenever total testosterone is at the low-normal end (8–12 nmol/L) or when SHBG is likely to be abnormal — common in obese, diabetic and older Indian men. A low free testosterone with a normal total reliably reclassifies many men into the hypogonadal range.
In women, free testosterone is the most sensitive marker of biochemical hyperandrogenism in PCOS and hirsutism workup — many women with classic PCOS clinical features have a normal total testosterone but a raised free testosterone because SHBG is low.
How to prepare
Morning sample (between 8 and 10 am) is essential — testosterone has a strong diurnal rhythm with peak in the early morning. Fasting is not required. Stop biotin for 48–72 hours. Mention any androgen / "T-booster" / anabolic steroid use. Acute illness lowers testosterone temporarily — repeat after recovery if needed.
Markers & reference ranges
Reference ranges below are typical adult values. Your lab's reported range may differ slightly based on the assay platform and patient demographics — always read your report against the range printed on it.
| Marker | Normal range | If low | If high |
|---|---|---|---|
| Free Testosterone (pg/mL)[1][2] | Adult male: 47 – 244 pg/mL · Adult female: 0.1 – 6.4 pg/mL (assay-dependent; calculated free T uses different units) | Low free testosterone in a man with consistent symptoms (fatigue, low libido, erectile dysfunction, depressed mood, decreased muscle mass) supports a diagnosis of hypogonadism. Confirm with LH and FSH to distinguish primary from secondary causes. In a woman, low free T is rarely clinically significant. | Raised free testosterone in a woman is a sensitive marker of biochemical hyperandrogenism (PCOS, non-classic CAH, androgen-secreting tumour). In men, a raised free testosterone may reflect exogenous androgen use or rare androgen-secreting tumour. |
When free testosterone changes the picture
| Patient | Total T | SHBG | Free T | Interpretation |
|---|---|---|---|---|
| Obese man, symptomatic | Borderline low | Low | Truly low | Hypogonadism confirmed by free T |
| Older man on no meds | Normal | High | Truly low | Age-related low free T despite normal total |
| Woman with PCOS / hirsutism | Normal | Low | Raised | Biochemical hyperandrogenism |
| Healthy young man | Normal | Normal | Normal | Normal |
| Anabolic steroid use | High | Low | Very high | Exogenous androgen |
Frequently asked questions
My total testosterone is normal but my doctor wants free testosterone — why?
Because SHBG (the binding protein) is often abnormal in obesity, diabetes, ageing or thyroid disease. A normal total testosterone with a high SHBG can hide a truly low free fraction. Free testosterone gives the answer the symptoms are pointing at.
Is free testosterone the same as bioavailable testosterone?
Not exactly. Free testosterone is the unbound fraction (~ 2%). Bioavailable testosterone is the free plus loosely albumin-bound fraction (~ 56% of total). Both are more biologically relevant than total T when SHBG is abnormal.
Which method of free testosterone is best?
Equilibrium dialysis followed by LC-MS/MS is the gold standard but expensive and limited in availability. The Endocrine Society endorses a calculated free testosterone (from total T + SHBG + albumin) as a reliable alternative — most Indian labs use this approach.
I am a woman — when is free testosterone useful?
In hirsutism, acne, hair loss and PCOS workup, free testosterone is more sensitive than total. Many women with PCOS have a normal total but raised free testosterone because their SHBG is suppressed by insulin resistance.
Why does the test have to be done in the morning?
Testosterone has a strong diurnal rhythm — values peak around 8 am and can be 30% lower by late afternoon. Morning sampling matches the reference ranges.
I am a man with low free testosterone — should I start testosterone gel?
Not on a single low result. Endocrine guidelines require two morning low values plus consistent symptoms before starting therapy, plus a check of LH/FSH, prolactin and ferritin to identify the cause. Treatment also carries fertility, cardiovascular and prostate considerations that need discussion.
Will it change after I lose weight?
Yes — meaningful weight loss in obese men raises SHBG and free testosterone, sometimes by 30–50%, and is the first-line non-drug treatment for obesity-related low testosterone.
Related Hormones / Endocrine tests
Tests commonly ordered alongside FREE TESTOSTERONE, or that help interpret an unexpected result.
Sources & references
- Endocrine Society — Testosterone Therapy in Men with Hypogonadism · accessed 2026-05-30T00:00:00.000Z
- Endocrine Society — Hirsutism in Premenopausal Women · accessed 2026-05-30T00:00:00.000Z
- NIH MedlinePlus — Testosterone Test · accessed 2026-05-30T00:00:00.000Z
- NCBI StatPearls — Free Testosterone · accessed 2026-05-30T00:00:00.000Z
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