An estimate of active (free) testosterone using total testosterone and SHBG when results seem unclear.
The free testosterone index, or FTI, is a simple calculated estimate of how much testosterone is unbound and available to your tissues. It is also known as the free androgen index.
The formula is: total testosterone divided by SHBG, multiplied by 100. It uses the ratio of testosterone to its main binding protein to gauge the active fraction.
Because most testosterone is bound to SHBG, the total level can be misleading when SHBG is high or low. The FTI corrects for this by relating testosterone directly to SHBG, giving a quick read on androgen status.
It is widely used in assessing women for high androgen states such as PCOS, and in men when symptoms do not match the total testosterone level.
Aniva reads your result against research-backed ranges, not just the lab's wide normal. The reference shown below is specific to this biomarker.
FTI is a unitless ratio and is strongly assay dependent:
| Group | Typical range |
|---|---|
| Men | about 30 to 150 |
| Women | about 0.5 to 7 |
Values depend on the testosterone and SHBG assays, so always read against your laboratory's reference interval.
As a calculated index it depends on the accuracy of both inputs. It is less reliable at very high SHBG. Testosterone peaks in the morning and varies day to day, and illness, obesity, and the contraceptive pill change SHBG.
Read alongside total testosterone, SHBG, and where available the directly measured free testosterone.
What does an FTI result mean in plain terms? It estimates how much testosterone is available to your body’s tissues. Higher suggests more active hormone; lower suggests less.
Do I need to fast? No. Fasting is not required for FTI. Morning collection is preferred, especially for men.
What can affect my result? Time of day, birth control or estrogen therapy, anabolic or antiandrogen medicines, thyroid or liver issues, weight changes, and high-dose biotin can all shift results.
How often should I test? Timing depends on symptoms and any treatment changes. Many recheck after several weeks to months to confirm trends.
How long do results take? Results are usually ready in about 7 days.
What should I discuss with my clinician? Share your symptoms, medicines, supplements, and life changes. Ask whether a validated calculated or direct free testosterone test would add clarity.
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