Insulin Dose–Adjusted HbA1c Misses Partial Remission in Youth, Especially With Higher BMI

Insulin dose–adjusted HbA1c (IDAA1c) ≤9 is widely used to define partial remission in pediatric type 1 diabetes and determine eligibility or outcomes in disease-modifying therapy trials. In an observational analysis published in Diabetes Care, researchers evaluated this measure in 422 SEARCH for Diabetes in Youth participants who underwent mixed-meal tolerance testing within 12 months of diagnosis. IDAA1c combines HbA1c (%) with four times the daily insulin dose in units/kg/day; the reference measure was stimulated area-under-the-curve mean C-peptide.

Participants with normal or underweight BMI had lower IDAA1c than those with overweight or obesity (8.95 versus 9.28; P = 0.043), despite lower stimulated C-peptide (1.25 versus 1.88 ng/mL; P < 0.001). For identifying C-peptide ≥0.91 ng/mL, IDAA1c ≤9 had 61% sensitivity and 79% specificity overall, with a reported ROC AUC of 0.77. In participants with overweight or obesity, sensitivity was 45% and specificity 81%.

A Youden index–derived cutoff of ≤11.6 increased sensitivity to 93% in the higher-BMI group but reduced specificity to 54%. These findings suggest the conventional cutoff can miss C-peptide–defined remission, particularly in higher-BMI youth, with implications for trial selection and outcome assessment. The alternative cutoff was derived from this analysis, and the available abstract does not report external validation. Findings are limited to assessment within the first year after diagnosis.