IDAA1c ≤9 missed more than half of partial remissions in youth with overweight or obesity

Design

Diagnostic accuracy analysis within an observational cohort

Population

422 youth with type 1 diabetes and mixed-meal stimulated C-peptide within 12 months of diagnosis

Primary outcome

Accuracy of IDAA1c ≤9 against C-peptide ≥0.91 ng/mL

Effect

Sensitivity 61%, specificity 79%, ROC AUC 0.77 overall; sensitivity 45% in overweight or obesity

The SEARCH for Diabetes in Youth study measured mixed-meal stimulated C-peptide in 422 young people within a year of type 1 diabetes diagnosis and compared it with the insulin dose-adjusted HbA1c, the usual bedside definition of partial remission.

Overall, IDAA1c ≤9 picked up 61% of those with C-peptide-defined remission. In youth with overweight or obesity it picked up 45%. These children had more residual beta-cell function than their leaner peers but scored worse on IDAA1c, because insulin resistance raises their insulin dose.

This matters most where IDAA1c is used as a gate: eligibility for teplizumab-style disease-modifying trials, and research outcomes. A higher, BMI-specific cutoff found more remissions but at the cost of many false positives. Where the answer changes a decision, a stimulated C-peptide is the better measure.

• IDAA1c is HbA1c (%) plus four times the total daily insulin dose in units/kg/day.
• Insulin resistance raises insulin needs in heavier children, pushing IDAA1c up even when C-peptide is preserved.
• Heavier youth had higher stimulated C-peptide (1.88 vs 1.25 ng/mL) yet higher IDAA1c.
• A cutoff of 11.6 caught 93% of remissions in this group but with only 54% specificity.
• Consider a mixed-meal stimulated C-peptide when remission status affects trial eligibility.

Why it matters

IDAA1c gates entry to disease-modifying trials and shapes insulin plans, and it systematically under-calls residual beta-cell function in the children most likely to be excluded.

Don't overread it

The study tested one cutoff in US youth; it does not establish a new validated threshold.

The statistics, in plain English

Sensitivity is how many true remissions the test catches; 45% means more than half were missed. Specificity is how many non-remissions it correctly rules out. An ROC area of 0.77 means fair, not good, discrimination. Raising the cutoff catches more cases but labels more people wrongly.

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