What it measures
Most testosterone in the blood is bound to proteins, mainly SHBG and albumin. Free testosterone is the small part that is not bound. This test measures it directly in the lab, rather than working it out from total testosterone and SHBG.
Why people test it
- Measured when total testosterone is borderline, or when SHBG is unusually high or low.
- Used when looking into low sex drive, erection problems or tiredness in men.
- Checked in women with excess hair growth or irregular periods, usually with total testosterone and SHBG.
- Monitored on TRT, where it shows how much testosterone is not bound to proteins.
Typical range
Ranges vary between labs, with the method used, age and sex, and your report shows the lab's own range. Labs measure free testosterone in different ways, so results from different labs are hard to compare.
Finger-prick or vein?
A vein draw is usually advised. Testosterone gels or creams on the fingers can contaminate a finger-prick sample and give a falsely high result.
Testosterone is highest in the morning, so the sample is usually taken in the morning.