Does a C-peptide of 8.87 with glucose 197 suggest insulin resistance?

A C-peptide of 8.87 paired with glucose 197 mg/dL is compatible with preserved, potentially substantial endogenous insulin secretion alongside inadequate glucose control. This pattern often occurs in insulin resistance, but the individual interpretation depends on the assay unit, sampling conditions, and kidney function.

Clinical interpretation

• C-peptide is released with insulin made by pancreatic beta cells and is absent from injected insulin. Glucose of 197 mg/dL is above the approximate 140–144 mg/dL threshold that stimulates C-peptide secretion, so this is a glucose-stimulated result if both were drawn simultaneously.
• If the C-peptide unit is ng/mL, 8.87 is above Mayo Clinic’s fasting reference interval (1.1–4.4 ng/mL), supporting substantial endogenous secretion rather than severe insulin deficiency.
• Elevated endogenous insulin secretion with persistent hyperglycemia is compatible with insufficient insulin effect in target tissues. In clamp studies, older adults had approximately 39% lower glucose disposal than younger adults despite similar insulin concentrations; other studies found 30–35% lower disposal under comparable hyperinsulinemia.

Mechanistic meaning

• Insulin resistance means skeletal muscle and other tissues do not adequately increase glucose uptake and/or the liver does not adequately suppress glucose output in response to insulin. Failure of glucose lowering despite insulin exposure therefore directly supports this physiology.
• C-peptide reflects secretion, not insulin sensitivity. Hyperglycemia, acute illness, inflammatory or stress hormones, glucocorticoids, and increased hepatic glucose production can all contribute to high glucose despite ongoing insulin production.

Key interpretive considerations

• Kidney clearance is crucial: C-peptide is mainly cleared by the kidneys, and chronic kidney disease can raise circulating C-peptide independently of pancreatic secretion.
• A single C-peptide–glucose pair cannot diagnose insulin resistance definitively; clamp-derived glucose disposal remains the reference measure.

Bottom line

• With ng/mL units and reasonably preserved renal function, C-peptide 8.87 at glucose 197 strongly suggests preserved endogenous insulin production and is consistent with insulin resistance, but it is supportive rather than diagnostic on its own.