Fasting insulin (revision 4)
Old revision·00:41, 6 Oct 2024·DEXA_Dilys
| 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]
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.