Background: Insulin autoimmune syndrome (IAS) is a rare condition in which spontaneous severe hypoglycemia without previous exposure to exogenous insulin, and is characterized by hyperinsulinemia and high titers of insulin autoantibodies (IAA).
Methods: This paper reports a case of IAS with false insulin test results due to the hook effect.
Results: The patient's blood samples were collected at 0, 30, 60, 120, 180 minutes for measurement of serum insulin after a 3-hour oral glucose tolerance test (OGTT). The results of serum insulin levels were 1,698.6 pmol/L at fasting, 1,633.05 pmol/L at 30 minutes post load, 1,691.14 pmol/L at 60 minutes post load, 1,780.67 pmol/L at 120 minutes post load, and 1,807.93 pmol/L at 180 minutes post load. Dilution and re-analysis of the specimens revealed that the actual insulin concentrations were 217,516 pmol/L at fasting, 228,456 pmol/L at 30 minutes post load, 250,474 pmol/L at 60 minutes post load, 273,266 pmol/L at 120 minutes post load, and 291,232 pmol/L at 180 minutes post load. The insulin level results before and after the dilution had significant discrepancies. It was the hook effect caused by the high concentration of insulin in the serum that made the first test inaccurate.
Conclusions: Serum insulin in patients with IAS is abnormally elevated, and extremely high concentrations of it may have a hook effect during assay resulting in inaccurate results. The laboratory should analyze and review the test results in combination with the patient's clinical case data, to detect interference in time and avoid erroneous diagnosis and treatment of patients.