The unbound (or loosely bound) testosterone fraction, often calculated from total testosterone and SHBG.
What it is
Free testosterone estimates the fraction not tightly bound to SHBG. Many UK reports use calculated free testosterone rather than direct assay.
Why it matters
Helpful when total testosterone and SHBG move in opposite directions. Sex, time of day, and assay method matter.
This guide is educational only and cannot diagnose you. Discuss results, especially anything outside your laboratory’s reference interval, or that does not match how you feel, with a GP or other appropriately qualified clinician.
How it affects the body
Androgen signalling influences muscle protein synthesis, libido, red-cell production, and mood: within a wider hormone network.
For athletes
Do not chase “optimisation” with unprescribed hormones. Low energy availability can suppress the axis.
