Testosterone, Free and Weakly Bound
Also known as: Bioavailable Testosterone, Free and Albumin-Bound Testosterone
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
Not provided.
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.
Methodology
Immunoassay (RIA)
Biomarkers
LOINC Codes
- 58716-2 - Testost free+WB + Total pnl SerPl
- 2986-8 - Testost SerPl-mCnc
- 6891-6 - Testosterone.free+WB MFr SerPl
- 2990-0 - Testosterone.free+WB SerPl-mCnc
Result Turnaround Time
1-6 days
Related Documents
For more information, please review the documents below
Specimen
Serum
Volume
2.3 mL
Minimum Volume
Not provided
Container
Red-top tube or gel-barrier tube
Collection Instructions
If a red-top tube is used, transfer separated serum to a plastic transport tube.
Storage Instructions
Room temperature
Causes for Rejection
Gross lipemia; recently administered isotopes
Stability Requirements
| Temperature | Period |
|---|---|
| Room Temperature | 14 days |
| Refrigerated | 14 days |
Other tests from different labs that may be relevant