Challenges in Measuring Glomerular Filtration Rate: A Clinical Laboratory Perspective  Jesse C. Seegmiller, John H. Eckfeldt, John C. Lieske  Advances in Chronic Kidney Disease  Volume 25, Issue 1, Pages 84-92 (January 2018) DOI: 10.1053/j.ackd.2017.10.006 Copyright © 2017 National Kidney Foundation, Inc. Terms and Conditions

Figure 1 (A) CE-UV electropherogram showing the internal standard, iothalamate, and coeluting interference signified by 1, 2, and 3, respectively, providing an iothalamate result of 2.2 g/mL. (B) LC-MS/MS chromatogram showing no interference using the m/z 614.8–456.0 multiple reaction monitoring (MRM), yielding an iothalamate concentration to be 10.1 mg/L. (C) LC-MS/MS chromatogram using the m/z 614.8–361.1 MRM where the interference was observed in U0. (D) The same U0 specimen where the interference was not observed with m/z 614.8–456.0 MRM. Abbreviations: CE-UV, capillary electrophoresis separation coupled with UV detection; LC-MS/MS, liquid chromatography tandem mass spectrometry. Reproduced with permission from the American Association for Clinical Chemistry (Seegmiller JC, Burns BE, Fauq AH, Mukhtar N, Lieske JC, Larson TS. Iothalamate quantification by tandem mass spectrometry to measure glomerular filtration rate. Clin Chem. 2010;56(4):568-574).mGFR=(U×V)P Equation 1: mGFR is the calculated GFR, U is the urinary concentration, V is the flow rate mL of urine produced per minute, and P is the plasma concentration.SurfaceareacorrectedmGFR=(U×V)P×1.73BSA Equation 2: Body surface area corrected mGFR is the calculated GFR and normalized to the patient's body surface area that is typically estimated from weight and height and one of several formulas,60,61 U is the urinary concentration, V is the flow rate mL of urine produced per minute, and P is the plasma concentration. Equation 3:mGFR=0.99078CL1−0.001218CL12 WhereCL1=Dose(mg)×EliminationRateConstantk(min−1)C0(mg/mL) AndLnC=LnC0−kt (C is the plasma concentration at time t, and C0 is the concentration at time 0). Advances in Chronic Kidney Disease 2018 25, 84-92DOI: (10.1053/j.ackd.2017.10.006) Copyright © 2017 National Kidney Foundation, Inc. Terms and Conditions