Fasting Insulin
Also written as: Insulin, Fasting
The pancreas hormone that moves sugar into cells, measured after an overnight fast.
What it measures
The concentration of insulin, the pancreas hormone that moves glucose from the blood into cells, after an overnight fast. Fasting standardizes the measurement, because insulin rises sharply after every meal.
Why a doctor orders it
Usually ordered alongside fasting glucose to see how much insulin the body is using to keep glucose steady. It comes up when insulin resistance, unexplained weight change, or episodes of low blood sugar are being evaluated.
What is generally associated with a higher result
Broadly associated with insulin resistance, a state where the body needs more insulin to achieve the same effect. Also linked with recent food intake, stress, steroid medicines, and, rarely, insulin producing tumors in the specific context of low glucose.
What is generally associated with a lower result
Broadly associated with reduced insulin production, but also seen with prolonged fasting and with lean, insulin sensitive physiology. The glucose value drawn at the same time carries much of the meaning.
Everyday things that move this number
Not every shift in a value reflects disease. These are ordinary factors known to affect this particular measurement:
- Any food or caloric drink before the draw, even a small one
- Stress and poor sleep the night before
- Vigorous exercise in the preceding day
- Steroid medicines and some hormonal treatments
- Sample handling: insulin degrades quickly if the sample is not processed promptly
Questions to take to your appointment
- Was glucose drawn at the same time, and how do the two values fit together?
- Exactly how long should the fast be before a repeat, and does black coffee count as breaking it?
- Could any of my current medicines be influencing this?
Build a printable questionnaire with your own results →
Where to read more
MedlinePlus, from the US National Library of Medicine, publishes patient-facing pages on individual lab tests and is a reliable next stop: medlineplus.gov/lab-tests .
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