In this study, Quadrupole Isotope Dilution Mass Spectrometry ((IDMS)-M-4) strategy was coupled with Liquid Chromatography-Quadrupole Time of Flight-Tandem Mass Spectrometry (LC-QTOF-MS/MS) for the accurate and precise determination of glycine in body fluids at trace levels. The instrumental variables such as column temperature, injection volume, sample/gas flow rates, fragmentor/capillary voltages, were optimized. Under the all optimized conditions, the calibration plot of glycine demonstrated a linearity ranging 5.0-100 mg kg(-1) and, the detection and quantification limits were obtained as 1.4 and 4.7 mg kg(-1), respectively. Superior enhancement was achieved for the accuracy and precision of proposed method when combined with (IDMS)-M-4 strategy. Percent recoveries of the proposed method for human plasma and urine spiked at 80 mg kg(-1) were calculated as 99.72 +/- 0.54% and 100.91 +/- 1.32%, respectively. These results validated the applicability of the method to complex matrices as well as confirming the high accuracy and precision. (C) 2019 Elsevier Ltd. All rights reserved.