Clinical and Interpretive

Insulin is a hormone produced by the beta cells of the pancreas. It regulates the uptake and utilization of glucose and is also involved in protein synthesis and triglyceride storage.

Type 1 diabetes (insulin-dependent diabetes) is caused by insulin deficiency due to the destruction of insulin-producing pancreatic islet (beta) cells. Type 2 diabetes (noninsulin-dependent diabetes) is characterized by resistance to the action of insulin (insulin resistance).

Insulin levels may be increased in patients with pancreatic beta cell tumors (insulinoma).

During prolonged fasting, when the patient’s glucose level is reduced to <40 mg/dL, elevated insulin level plus elevated levels of proinsulin and C-peptide suggests insulinoma.

Insulin levels generally decline in patients with type 1 diabetes mellitus.

In the early stage of type 2 diabetes, insulin levels are either normal or elevated. In the late stage of type 2 diabetes, insulin levels decline.

In normal individuals, insulin levels parallel blood glucose levels.

To compare insulin and C-peptide concentrations (ie, insulin to C-peptide ratio):

-Convert insulin to pmol/L: insulin concentration in µIU/mL x 6.945 = insulin concentration in pmol/L.

-Convert C-peptide to pmol/L: C-peptide concentration in ng/mL x 331 = C-peptide concentration in pmol/L.