Agreement between Self-Reported and Laboratory-Measured HbA1c in the T1D Exchange Registry

Author Block: JAIME LUCOVE, HUYEN T. NGUYEN, ALEXANDRIA RATZKI-LEEWING, Boston, MA, Baltimore, MD

Introduction and Objective: Although prior studies suggest high agreement between self-reported and laboratory-measured (LAB) HbA_1c, evidence from large, contemporary type 1 diabetes (T1D) populations is limited. This study evaluated how well self-reported HbA_1c corresponds to LAB HbA_1c in the T1D Exchange Registry, both across observed values and classification at the clinically relevant threshold of 7%.

Methods: This cross-sectional study analyzed data from adults (≥18 years) enrolled in the T1D Exchange Registry, a direct-to-participant registry. Self-reported HbA_1c from questionnaires was paired with NorstellaLinq laboratory HbA_1c from the same or prior month using privacy-preserving record linkage. Correlation between self-reported and LAB HbA_1c was assessed using Kendall’s Tau. For the HbA_1c threshold ≥ 7% versus < 7%, differences in paired proportions were tested using McNemar’s chi-squared test, and sensitivity, specificity, positive and negative predictive values were calculated.

Results: Among 1,710 participants, 2,995 paired self-reported and LAB HbA_1c values were available. Mean self-reported HbA_1c (6.76% [SD 1.13]) and LAB HbA_1c (6.78% [SD 1.16]) were strongly correlated (τ = 0.90, p < .001). The proportion of participants with HbA_1c ≥7% did not statistically significantly differ between self-reported (35.2%) and LAB (35.3%) values (McNemar’s χ² = 0.08, p = .78). Using LAB HbA_1c ≥7% as the reference standard, self-reported HbA_1c demonstrated high classification performance: sensitivity=0.95, specificity=0.97, positive predictive value=0.95, and negative predictive value=0.97.

Conclusion: In the T1D Exchange Registry, self-reported HbA_1c closely approximates LAB values, showing very strong correlation and high accuracy for classifying individuals relative to the 7% glycemic target. These results support the use of self-reported HbA1c as a valid measure for registry-based research in real-world adult populations with T1D.

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