What does the Fasting Insulin test measure?

Why is Fasting Insulin measured?

Fasting insulin is the functional marker of insulin resistance — a key driver in PCOS, metabolic syndrome, non-alcoholic fatty liver disease, cardiovascular risk, and weight management difficulty. Standard fasting glucose and HbA1c can remain normal while fasting insulin is substantially elevated, representing early insulin resistance that is missed by standard glycaemic markers alone. In female health panels, fasting insulin is critical for characterising the metabolic driver of androgen excess, SHBG suppression, and ovulatory dysfunction in PCOS and premenopausal metabolic syndrome.

Reference ranges

Standard reference

2–19 µIU/mL (14–132 pmol/L) # REVIEWER FLAG: Confirm Access Medical Laboratories fasting insulin reference range — laboratory reference intervals vary substantially. The functional medicine optimal range is considerably narrower than most laboratory reference ranges.

Functional medicine optimal

<5 µIU/mL (functional medicine optimal; HOMA-IR <1.0 calculated from fasting insulin and fasting glucose). # REVIEWER FLAG: Fasting insulin optimal of <5 µIU/mL is used in functional medicine but is not a standardised clinical guideline threshold — reviewer to confirm framing.

Units

pmol/L, µU/mL, µIU/mL

Reference ranges vary by laboratory and assay platform. Interpret in context of the issuing laboratory's stated range.