Chemical Pathology


  • 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

Sample requirements

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

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

5ml gold tube


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; FAI will not then be reportable. 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.

Age FAI %
20 - 50 years 0.18 - 7.07
>50 years 0.10 - 4.95