Clinical Significance

   It is useful for : Diagnosing insulinoma, when used in conjunction with proinsulin and C-peptide measurements, Management of diabetes mellitus.

Specimen

   Serum

Stability

   Frozen (preferred) : 180 days

   Refrigerated : 7 days

Reference Range

   3 – 7 uIU/ml

Interpretation

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

Limitation

   This assay has 100% cross-reactivity with recombinant human insulin (Novolin R and Novolin N). It does not recognize other commonly used analogues of injectable insulin (ie, insulin lispro, insulin aspart, and insulin glargine).