Free (Bioactive) Insulin Test
This test measures the level of free insulin circulating in the blood — insulin not bound to insulin antibodies — as distinct from total insulin. Quest requires an overnight fast before the blood draw.
About this test
Insulin, Free (Bioactive) measures the portion of insulin in the blood that is not bound to insulin antibodies, using immunoassay on a serum sample. Quest describes this measurement as helping to interpret blood sugar concentration in relation to insulin injections in insulin-treated people who have developed insulin antibodies, a situation where a total insulin measurement can be harder to interpret on its own.
Because antibody binding can affect how much insulin appears "free" versus bound, this test is specific to that clinical picture rather than a general insulin check. Quest lists it under names including Biologically Active Insulin, Free Insulin and Non-AB Bound Insulin, which describe the same free-insulin measurement.
Who might consider this test?
- The free insulin result is meant to be read alongside blood glucose and the person's insulin treatment history.
Test details
| Collection | Quest patient service center |
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Quest resources
Additional details
What this test looks at
The test reports the concentration of free, unbound insulin in a 0.5 mL serum sample. Quest requires an overnight fast before the blood draw, and the result is intended to be read together with blood glucose concentration and insulin dosing history rather than as a stand-alone number.
This test isn't part of the Celio Health store at the moment, so it can't be ordered or requested here. The test menu lists everything that can.
Laboratory results should always be interpreted by a licensed clinician who knows your health history. This page is information about a test, not medical advice.
Frequently asked questions
What does this test measure?
It measures free insulin — the portion not bound to insulin antibodies — in a serum sample, as distinct from total insulin.
How is the sample collected?
The test uses a 0.5 mL serum sample from a routine blood draw.
Do I need to prepare for this test?
Yes. Quest lists an overnight fast before the blood draw for this test.
Who is this test usually for?
Quest describes it as used to help interpret blood sugar concentration in relation to insulin injections in insulin-treated people who have developed insulin antibodies.
Is this the same as a standard insulin test?
No. This measures free, unbound insulin specifically, which differs from a total insulin measurement.