Specimen Requirements


Testosterone, Free, Bioavailable and Total

Specimen Requirement

Collect SST/2.3 mL serum, after 30 minutes of clotting promptly centrifuge and send.

Alternate collection: Collect red top, centrifuge and transfer 2.3 mL serum to a screw top plastic vial, indicate sample type on tube and send.


Ammonium sulfate precipitation; radioassay


Room temp: 14 days, Refrigerated: 14 days, Frozen: Not accepted

Reference Range

The reference range is determined by the performing laboratory and will show on the report.


2-6 days

Clinical Use

Free and weakly bound testosterone (FWBT), also referred to as bioavailable testosterone, is thought to reflect an individual’s biologically active, circulating testosterone. FWBT includes free testosterone and testosterone that is bound to albumin. FWBT does not include sex hormone binding globulin-bound testosterone.

Test Code