Testosterone, Free and Weakly Bound

Casandra

Casandra Test Code LC78886Version 1 (DRAFT)

Performing Lab

Lab LabcorpLab Test ID 143255CPT Code 84410

Testosterone, Free and Weakly Bound

Also known as: Bioavailable Testosterone, Free and Albumin-Bound Testosterone

Clinical Use

Order Test

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. The SHBG-bound fraction is biologically inactive because of the high binding affinity of SHBG for testosterone. The rapid dissociation of “weakly bound” testosterone from albumin results in the availability of essentially all albumin-bound testosterone for steroid-receptor interaction.1

Special Instructions

This panel includes Testosterone, Total, which may be affected by biotin supplements. Patients should cease biotin consumption 72 hours before sample collection. The test involves selective precipitation of SHBG with ammonium sulfate. Details in sample report PDF.

Limitations

The measurement of FWBT might give misleading results if the patient is taking supplements with high doses of biotin. An elevated level of FWBT in women can indicate hyperandrogenism. In men, decreased FWBT levels are associated with hypogonadism and low libido. Men’s FWBT levels drop more rapidly than total testosterone as they age. During pregnancy, FWBT levels can rise but typically remain within reference limits.

Test Details