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.
The measurement of free and weakly bound testosterone in women, when used in conjunction with the assay of the DHEA-S and SHBG, can be used to establish etiology of hirsutism.
- Total testosterone levels in women decrease by approximately 30% after menopause.
- Decreased FWBT levels have been associated with diminished libido and loss of bone density.
- Administration of exogenous estrogens has the physiologic effect of increasing SHBG concentrations and suppressing the production of androgens by the ovary. This results in a net decrease in FWBT.
In males, decreased serum concentrations are associated with hypogonadism.
FWBT levels in males fall with age at a rate that exceeds that of total testosterone and parallels the drop in DHEA sulfate.
This decrease is thought to be caused by diminished testicular production and not due to hypothalamic/pituitary insufficiency.
Decreased FWBT was not, however, found to correlate with diminished potency. Since SHBG has been found to increase with age, the FWBT level may be a more reliable indicator of testosterone production than total testosterone.
Elevated levels of FWBT are observed in female hirsutism.
FWBT levels tend to increase during pregnancy but have been found to remain below the upper limit of the reference interval.
Own it for life
Our exclusive data entry service is a convenient way to get your results into your private dashboard. Simply attach an image or a file of your lab test results, and one of our qualified data entry team members will add the results for you. We support all sorts of files, whether PDFs, JPGs, or Excel. This service is excellent whether you have a lot of reports to upload or are too busy to do the data entry yourself.
We strive to make the data entry process easy for you. Whether by offering dozens of templates to choose from that pre-populate the most popular laboratory panels or by giving you instant feedback on the entered values. Our data entry forms are an easy, fast, and convenient way to enter the reports yourself. There is no limit on how many lab reports you can upload.
billed every month
Data entry included
$6.60/month billed annually
Data entry included
own it for life
Are You a Health Professional?
Get started with our professional plan
Welcome to Healthmatters Pro.
Save time on interpreting lab results with the largest database of biomarkers online. In-depth research on any test at your fingertips, all stored and tracked in one place. Learn more
Pro Monthly Plus
for health professionals
$75 per month