Non-invasive ¹³C-glucose breath test using residual gas analyzer-mass spectrometry: A novel tool for screening individuals with pre-diabetes and type 2 diabetes

We report, for the first time, the clinical feasibility of a novel residual gas analyzer mass spectrometry (RGA-MS) method for accurate evaluation of the ¹³C-glucose breath test (¹³C-GBT) in the diagnosis of pre-diabetes (PD) and type 2 diabetes mellitus (T2D). In T2D or PD, glucose uptake is impaired and results in blunted isotope enriched ¹³CO ₂ production in exhaled breath samples. Using the Receiver operating characteristics (ROC) curve analysis, an optimal diagnostic cut-off point of the ¹³CO₂/¹²CO₂ isotope ratios expressed as the delta-over-baseline (DOB) value, was determined to be δ_DOB¹³C‰ = 28.81‰ for screening individuals with non-diabetes controls (NDC) and pre-diabetes (PD), corresponding to a sensitivity of 100% and specificity of 94.4%. We also determined another optimal diagnostic cut-off point of δ _DOB¹³C‰ = 19.88‰ between individuals with PD and T2D, which exhibited 100% sensitivity and 95.5% specificity. Our RGA-MS methodology for the ¹³C-GBT also manifested a typical diagnostic positive and negative predictive value of 96% and 100%, respectively. The diagnostic accuracy, precision and validity of the results were also confirmed by high-resolution optical cavity enhanced integrated cavity output spectroscopy (ICOS) measurements. The δ_DOB¹³C‰ values measured with RGA-MS method, correlated favourably (R² = 0.979) with those determined by the laser based ICOS method. Moreover, we observed that the effects of endogenous CO₂ production related to basal metabolic rates in individuals were statistically insignificant (p = 0.37 and 0.73) on the diagnostic accuracy. Our findings suggest that the RGA-MS is a valid and sufficiently robust method for the ¹³C-GBT which may serve as an alternative non-invasive point-of-care diagnostic tool for routine clinical practices as well as for large-scale diabetes screening purposes in real-time.