Fasting insulin
A blood test that measures insulin, not glucose, after fasting. More sensitive to early insulin resistance than fasting glucose.
Fasting insulin is a single blood draw, taken after roughly eight or more hours without food, that measures the level of insulin rather than glucose.
It matters in PMOS because the most common test, fasting glucose, measures the wrong thing for early insulin resistance. As resistance develops, the pancreas releases more insulin to keep glucose normal. Glucose stays in range while insulin climbs. A fasting insulin test can see that climb directly.
A high fasting insulin in the context of normal fasting glucose is a strong hint of compensatory hyperinsulinaemia. It is also one of the two inputs used to calculate HOMA-IR. If you have PMOS and have only had fasting glucose checked, asking to add fasting insulin is a reasonable next step.