Validity of triple- and dual-tracer techniques to estimate glucose appearance

Abstract

The triple-tracer (TT) dilution technique has been proposed to be the gold standard method to measure postprandial glucose appearance. However, validation against an independent standard has been missing. We addressed this issue and also validated the simpler dual-tracer (DT) technique. Sixteen young subjects with type 1 diabetes (age 19.5 ± 3.8 yr, BMI 23.4 ± 1.5 kg/m(2), HbA(1c) 8.7 ± 1.7%, diabetes duration 9.0 ± 6.9 yr, total daily insulin 0.9 ± 0.2 U·kg(-1)·day(-1), mean ± SD) received a variable intravenous 20% dextrose infusion enriched with [U-(13)C]glucose over 8 h to achieve postprandial-resembling glucose excursions while intravenous insulin was administered to achieve postprandial-resembling levels of plasma insulin. Primed [6,6-(2)H(2)]glucose was infused in a manner that mimicked the expected endogenous glucose production and [U-(13)C; 1,2,3,4,5,6,6-(2)H(7)]glucose was infused in a manner that mimicked the expected glucose appearance from a standard meal. Plasma glucose enrichment was measured by gas chromatography-mass spectrometry. The intravenous dextrose infusion served as an independent standard and was reconstructed using the TT and DT techniques with the two-compartment Radziuk/Mari model and an advanced stochastic computational method. The difference between the infused and reconstructed dextrose profile was similar for the two methods (root mean square error 6.6 ± 1.9 vs. 8.0 ± 3.5 μmol·kg(-1)·min(-1), TT vs. DT, P = NS, paired t-test). The TT technique was more accurate in recovering the overall dextrose infusion (100 ± 9 and 92 ± 12%; P = 0.02). The root mean square error associated with the mean dextrose infusion profile was 2.5 and 3.3 μmol·kg(-1)·min(-1) for the TT and DT techniques, respectively. We conclude that the TT and DT techniques combined with the advanced computational method can measure accurately exogenous glucose appearance. The TT technique tends to outperform slightly the DT technique, but the latter benefits from reduced experimental and computational complexity.

Fig. 1.

Experimental study protocol.

Fig. 2.

Concentration of plasma glucose (top; mean ± SE) and plasma insulin [bottom; median (IQR)] during the time course of the experiment (n = 16).

Fig. 3.

Tracer-to-tracee ratios (TTRs) used by triple-tracer and dual-tracer techniques. Top: TTR of G_EM/G_E ([6,6-²H₂]glucose over endogenous glucose). Middle: TTR of G_MM/G_M ([U-¹³C; 1,2,3,4,5,6,6-²H₇]glucose over [U-¹³C]glucose). Bottom: TTR of G_EM/G_M ([6,6-²H₂]glucose over [U-¹³C]glucose) (means ± SE; n = 16).

Fig. 4.

Sample dextrose infusion profile and reconstructed infusion profiles estimated by triple-tracer (TT) and dual-tracer (DT) methods.

Fig. 5.

Top: mean dextrose infusion profile and mean reconstructed profiles calculated by TT and DT methods. Bottom: differences between actual and reconstructed profiles associated with TT and DT methods (means ± SE; n = 16).

Fig. 6.

Top: mean endogenous glucose production (EGP) and R_d profiles calculated by TT and DT methods. Bottom: differences between EGP and R_d profiles calculated by te DT and TT methods (means ± SE; n = 16).

Fig. 7.

Mean fractional clearance rates of EM and MM glucose tracers estimated by the TT method and the mean fractional clearance rate of the EM glucose tracer estimated by the DT method (n = 16).