Fasting insulin (revision 8)
Old revision·06:40, 5 Dec 2024·StubSorterBot
| Fasting insulin | |
|---|---|
| Specimen | Fasting plasma or serum |
| Interpretable | Only alongside a simultaneous glucose |
| Standardisation | Poor between assays |
| Topic infobox · conventions | |
Fasting insulin is the concentration of insulin measured after an overnight fast. It is widely available and widely over-interpreted: an insulin value alone answers no question, because the same concentration means different things at different glucose concentrations.[1]
Insulin immunoassays are poorly standardised between manufacturers, differing in cross-reactivity with proinsulin and its split products. Values from different laboratories are not interchangeable, and derived indices inherit the discrepancy.[1]
Its principal use is as an input to derived indices, chiefly HOMA-IR and HOMA-B, which combine it with fasting glucose to estimate insulin resistance and secretory capacity respectively.[2]
Why it needs glucose alongside it
[edit]Insulin secretion is a response to glucose. A high fasting insulin with a normal fasting glucose indicates that normal glucose is being maintained at the cost of high insulin — the signature of insulin resistance with preserved secretion. The same insulin with a high glucose indicates resistance with inadequate compensation.[1]
A low insulin with a high glucose indicates secretory failure. A low insulin with a normal glucose is unremarkable. The four combinations mean four different things, and only two values together distinguish them.
This is why laboratory reports that give an insulin reference interval without reference to glucose are of limited use, and why the derived indices exist at all.[2]