ABSTRACT
Background: Deuterium dilution is the criterion method to quantify total body water (TBW) in humans and to estimate body composition and hydration. Dilution of deuterated water in the body can be estimated from saliva, urine, or blood samples. The gold standard for quantifying isotope fractions is isotope ratio mass spectroscopy (IRMS);Fourier Transfer Infrared Spectroscopy (FTIR) is another less validated method that is more accessible. Few studies compare the precision and accuracy of TBW where samples are analyzed at different laboratories using different techniques and/or types of samples. In this study, we compare results from three laboratories using blinded duplicate samples of either saliva or urine measured using either FTIR or IRMS. Methods: The DaKine study recruited 80 athletes for multiple body composition measures. Each participant had 9 ml of both urine and saliva collected at baseline, 3 and 4-hour time points following the International Atomic Energy Agency protocol. The samples were aliquoted into 30 divisions providing blindedduplicate samples to three laboratories for both urine and saliva. Lab1 used IRMS for urine. Lab2 used IRMS to process saliva and urine, while Lab3 used FTIR to process saliva and urine. Results: Because of the temporary closure of the laboratories due to Covid-19, urine samples from only 24 of the 80 subjects have been processed by the laboratories so far. The test-retest RMSE (%CV) for urine was as follows: Lab1=0.25 L (0.55%);Lab2=0.24 L (0.60%);Lab3=pending. For saliva, the precision was: Lab1=unavailable;Lab2=0.26 L (0.63%);Lab3=pending. The accuracy between laboratories for urine measures was Lab2=0.98Lab1 -.024, R2=0.98, RMSE=1.31. Intra-laboratory comparison of urine and saliva was Lab2(urine)=1.01Lab2-.08, R2=0.98, RMSE=1.2. Conclusions: We conclude that inter-lab urine samples using IRMS are highly accurate (R2 = 0.98) to one another with precisions less than 1%. Intralab lab saliva and urine comparisons had similar accuracy and precision.