Free Androgen Index (FAI)

Clinical Biochemistry

Background Information

• The free androgen index (FAI) is a recommended baseline investigation for suspected hyperandrogenism in women.
• Free androgen index (FAI) = Total Testosterone/SHBG x 100 %
• Samples should be collected early morning (8am to 11am)
• Results should be interpreted with caution in the presence of abnormal albumin levels

Patient Preparation

If patient on high dose biotin therapy (>5mg/day) collect sample at least 8 hours after the last dose.

Sample Requirements

For adults, blood taken into a 5mL gold top gel tube (or rust top for the Acute Unit)

Storage/Transport

Send at ambient temperature to the laboratory. If unavoidable, samples can be stored refrigerated overnight.

Required Information

Relevant clinical details including the reason for testing.

Turnaround Times

Results are normally available within 10 days, however if the initial immunoassay testosterone level is found to be significantly raised then samples will be referred for confirmation of the testosterone result by tandem mass spectrophotometry (MS). The tandem MS testosterone result is expected back within 4 weeks.

Reference Ranges

Female Reference Ranges:

• FAI reference ranges only applicable when testosterone and SHBG have been assayed by local Roche immunoassay and when albumin is within the reference range.

Further Information

For more information, visit the International Guideline for PCOS

Page last updated: 15/10/2025 | Page last reviewed: 15/10/2025