Objective: This study investigated whether the delta-over-baseline of exhaled 13CO2 (Δ13CO2), generated from a 13C glucose breath test (13C-GBT), measured insulin resistance (IR) in people with type 1 diabetes, using the hyperinsulinemic-euglycemic clamp (HEC) as reference method. Secondary objective was to compare the 13C-GBT with the estimated glucose disposal rate (eGDR).
Methods: A 40 mU/m2/min HEC and two separate 13C-GBTs (euglycemic with insulin bolus and hyperglycemic without bolus) were consecutively performed in 44 adults with type 1 diabetes with varying body compositions. eGDR was calculated based on HbA1c, presence of hypertension and waist circumference.
Results: Mean M-value was 5.9 ± 3.1 mg/kg/min, mean euglycemic Δ13CO2 was 6.4 ± 2.1 δ‰, while median eGDR was 5.9 [4.3 - 9.8] mg/kg/min. The hyperglycemic Δ13CO2 did not correlate with the M-value, while the euglycemic Δ13CO2 and the M-value correlated strongly (r = 0.74, p < 0.001). Correlation between M-value and eGDR was more moderate (Spearman's rho = 0.63, p < 0.001). Linear regression showed an association between Δ13CO2 and M-value, adjusted for age, sex and HbA1c (adjusted R² = 0.52, B = 1.16, 95% CI 0.80 - 1.52, p < 0.001). The AUROC for Δ13CO2 to identify subjects with IR (M-value < 4.9 mg/kg/min) was 0.81 (95% CI 0.68 - 0.94, p < 0.001). The optimal cut-off for Δ13CO2 to identify subjects with IR was ≤ 5.8 δ‰.
Conclusions: Under euglycemic conditions, the 13C-GBT accurately identified individuals with type 1 diabetes and concurrent IR, suggesting its potential as a valuable non-invasive index.
Keywords: 13C glucose breath test; Type 1 diabetes; hyperinsulinemic-euglycemic clamp; insulin resistance; insulin-mediated glucose metabolism.
© The Author(s) 2024. Published by Oxford University Press on behalf of the Endocrine Society. All rights reserved. For commercial re-use, please contact reprints@oup.com for reprints and translation rights for reprints. All other permissions can be obtained through our RightsLink service via the Permissions link on the article page on our site—for further information please contact journals.permissions@oup.com.