The unbound, biologically active fraction of testosterone.
Free testosterone is the small fraction of testosterone that circulates unbound to any protein, so it is fully available to your tissues. This test measures it directly rather than calculating it.
Only a few percent of total testosterone is free, so the direct measurement is sensitive to method. It is taken from a morning serum sample because testosterone is highest early in the day.
Free testosterone reflects the active hormone better than total testosterone when binding proteins are unusual. It helps explain symptoms of low or high androgen activity that the total level alone does not.
Low free testosterone can contribute to low energy, low libido, and reduced muscle and bone strength. High levels in women can point to androgen excess such as PCOS.
Aniva reads your result against research-backed ranges, not just the lab's wide normal. The reference shown below is specific to this biomarker.
Typical adult male guidance, assay dependent:
| Result | Range |
|---|---|
| Free testosterone (men) | 0.2 to 0.62 nmol/L |
Roughly 5.5 to 18 ng/L. Values are much lower in women and depend heavily on the method. Read against your lab's reference interval.
Free testosterone varies through the day and peaks in the morning. Direct immunoassays can be less accurate than equilibrium methods. Illness, obesity, and medicines that change SHBG affect interpretation. Biotin can interfere with some assays.
Read alongside total testosterone, SHBG, and the free testosterone index.
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