Bioavailable Testosterone (BIO-T)

What is Bioavailable Testosterone?

Bioavailable testosterone represents the portion of testosterone that’s either free (unbound) or loosely bound to albumin, making it readily available to tissues. It’s calculated from total testosterone, SHBG, and albumin levels, providing a better assessment of testosterone activity than total testosterone alone.

Why is it Tested?

Doctors order bioavailable testosterone when total testosterone results don’t match clinical symptoms, particularly in cases where SHBG levels are abnormal. It helps identify testosterone deficiency or excess when other markers are inconclusive, especially in older men or those with metabolic conditions.

Normal Ranges

Reference ranges vary by lab, age, and sex. General adult guidelines:

Men (20–30 years): 130–680 ng/dL
Men (30–40 years): 110–570 ng/dL
Men (40–50 years): 95–440 ng/dL
Men (50+ years): 85–350 ng/dL
Women: 2–20 ng/dL

Ranges decline with age due to natural hormonal changes.

Reference ranges vary by authority. Track yours across multiple standards with automatic unit conversions in LabsVault.

What do Abnormal Results Mean?

Abnormal results are not a diagnosis. Always discuss your results with a qualified healthcare provider before making any medical decisions.

Low Bioavailable Testosterone

Low levels may indicate:

Hypogonadism (primary or secondary)
Age-related decline
Chronic illness or stress
Medications affecting hormone production

High Bioavailable Testosterone

Elevated levels may suggest:

Anabolic steroid use
Certain tumors
Congenital adrenal hyperplasia
PCOS (in women)

How to Track Over Time

Bioavailable testosterone provides insight into functional hormone status that total testosterone might miss. Tracking trends helps distinguish normal aging from pathological decline and monitors response to hormone replacement therapy or lifestyle interventions.

Bioavailable Testosterone