A Sensitive Plasma Insulin Immunoassay to Establish the Diagnosis of Congenital Hyperinsulinism

Abstract

Background: The diagnosis of congenital hyperinsulinism (CHI) may be hampered by a plasma (p-) insulin detection limit of 12-18 pmol/L (2-3 mU/L).

Objective: To evaluate the diagnostic performance of a sensitive insulin immunoassay and to find the optimal p-insulin cut-off for the diagnosis of CHI.

Methods: Diagnostic fasting tests, performed without medication or i.v.-glucose, were investigated in children with a clinical diagnosis of CHI, or idiopathic ketotic hypoglycemia (IKH). The CHI diagnosis was either clinical or by the alternative, p-insulin-free criteria; hypoglycemia plus disease-causing genetic mutations and/or CHI-compatible pancreatic histopathology. We included diagnostic p-insulin samples with simultaneous p-glucose <3.2 mmol/L and used a sensitive insulin assay (Cobas e411 immunoassay analyzer; lower detection limit 1.2 pmol/L; normal range 15.1-147.1 pmol/L). Receiver operating characteristics area under the curve (ROC AUC) values and optimal cut-offs were analyzed for the performance of p-insulin to diagnose CHI.

Results: In 61 CHI patients, the median (range) p-insulin was 76.5 (17-644) pmol/L compared to 1.5 (1.5-7.7) pmol/L in IKH patients (n=15). The ROC AUC was 1.0 for the diagnosis of CHI defined both by the clinical diagnosis (n=61) and by alternative criteria (n=57). The optimal p-insulin cut-offs were 12.3 pmol/L, and 10.6 pmol/L, at p-glucose <3.2 mmol/L (n=61), and <3.0 mmol/L (n=49), respectively.

Conclusions: The sensitive insulin assay performed excellent in diagnosing CHI with optimal p-insulin cut-offs at 12.3 pmol/L (2.0 mU/L), and 10.6 pmol/L (1.8 mU/L), at p-glucose <3.2 mmol/L, and <3.0 mmol/L, respectively. A sensitive insulin assay may serve to simplify the diagnosis of CHI.

Keywords: children; congenital hyperinsulinism; diagnostic performance; hypoglycemia; immunoassays.

Figure 1

Patient inclusion flowchart. CHI, congenital hyperinsulinism; IKH, idiopathic ketotic hypoglycemia; p, plasma.

Figure 2

Two-way scatter-plot showing the association between p-insulin and p-glucose, split by IKH and subtypes of CHI. The X-axis is in logarithmic scale. Gray area indicates the normal insulin reference range 15.1–147.1 pmol/L for normal fasting glucose concentrations. +, IKH; ◆ and ◇, diffuse CHI; • and ○, focal CHI; Δ, atypical CHI; □, CHI with unknown histology. Closed symbols, K_ATP-channel mutations. Open symbols, no K_ATP -channel mutations.

Figure 3

ROC-curves performed for the four predefined groups including cut-offs and 95% CI. Critical samples of p-insulin when simultaneous p-glucose was <3.2 mmol/L or <3.0 mmol/L. Alternative diagnosis of CHI was based on p-insulin free criteria.