Performance of the equations to estimate the glomerular filtration rate in Mexican patients receiving kidney transplantation

Gaceta Médica de México ORIGINAL ARTICLE Performance of the equations to estimate the glomerular filtration rate in Mexican patients receiving kidney transplantation Jaime Antonio Borjas-García,1 Everardo Lugo-Vega,1 Lilia María de Guadalupe Llamazares-Azuara1 and Marco Ulises Martínez-Martínez2* 1 Hospital Central “Dr. Ignacio Morones Prieto”, Department of Nephrology; 2Instituto Mexicano del Seguro Social, Department of Internal Medicine. San Luis Potosí, Mexico Abstract Introduction: The management of kidney transplant recipients requires glomerular filtration rate (GFR) monitoring, which is an indicator of graft primary function and patient survival. Objective: To evaluate the performance of different creatinine or cystatin-based formulas in the estimation of glomerular filtration rate in Mexican patients receiving kidney transplantation. Method: 30 transplant recipients were included, in whom the glomerular filtration rate was measured by means of iothalamate, and was also calculated using seven equations based on cystatin or creatinine. Results: The formula with the best performance was the one proposed by the chronic kidney disease epidemiology collaboration (CKD-EPI), with a bias of −2.4 mL/min/1.73 m2 and an accuracy of 9.6; 96.7 % of patients were within 30 % of the measured GFR. The second best formula was the modification of diet in renal disease (MDRD) equation. Cystatin-based equations showed a poor performance. Conclusions: Our study suggests that, in Mexican patients receiving kidney transplantations, the best equations to estimate GFR are the CKD-EPI and MDRD equations. KEY WORDS: Glomerular filtration rate. Kidney transplantation. Kidney function. Chronic Kidney Disease Epidemiology Collaboration Modification of Diet in Renal Disease. Creatinine clearance. Introduction Kidney transplantation is the treatment of choice in patients with chronic kidney disease, it is more effective and less costly than replacement therapy.1,2 Management of transplant recipient patients requires glomerular filtration rate (GFR) assessment, which is an indicator of graft primary function and long-term survival;3 moreover, GFR is an independent risk factor for cardiovascular mortality,4 which is the leading cause of death in kidney transplant recipients.5 GFR estimation should be as accurate as possible and, in this sense, the gold standard is inulin; however, owing to the difficulties for measuring GFR by this 206 method, different creatinine or cystatin-based equations have been proposed.6 Creatinine has limitations for being the ideal GFR marker because it depends on muscle mass, tubular secretion and others; cystatin can also show variations depending on the method by means of which it is measured and might have variations in patients with hypothyroidism, cirrhosis or receiving certain medications.7 For that reason, it is suggested that all equations should be assessed in populations other than those where they were developed, calculating accuracy, precision and bias.6 The purpose of this study was to assess the performance in the estimation of kidney function with creatinine clearance (CrCl) and with the Cockcroft-Gault Correspondence: Date of reception: 11-04-2018 *Marco Ulises Martínez-Martínez Date of acceptance: 24-01-2019 Contents available at PubMed E-mail: DOI: 10.24875/GMM.M18004335 www.gacetamedicademexico.com Gac Med Mex. 2019;155:206-210 Borjas-García JA, et al.: Glomerular filtration and transplants (C-G),8 Modification of Diet in Renal Disease (MDRD),9 Chronic Kidney Disease Epidemiology Collaboration (CKD-EPI),10 Mayo Clinic Quadratic (MCQ) equation,11 Stevens-3 (third equation based on cystatin and creatinine according to Stevens et al.)12 and CKD-EPI cystatin/creatinine (CKD-EPI Cys-Cr) formulas13 in kidney transplant recipients under the care of the outpatient clinic of the “Dr. Ignacio Morones Prieto” Central Hospital Nephrology Division, in San Luis Potosí, Mexico. Method Patients older than 18 years, who were renal transplantation recipients, and who were under the care of the Central Hospital “Dr. Ignacio Morones Prieto” Nephrology Division were included. Patients who attended the nephrology outpatient clinic were invited to participate in the study, which was approved by the Ethics Committee; those who agreed to participate had to sign the informed consent form. Patients with at least three months from having received the kidney transplant were included. Pregnant patients, patients with a history of acute rejection, on replacement therapy with peritoneal dialysis or hemodialysis, chronic liver disease, hypothyroidism or allergy to the contrast medium were excluded. Creatinine values were standardized according to Roche enzymatic method. Cystatin C was measured using the enzyme-linked immunosorbent assay (ELISA) method. The reference standard was iothalamate clearance, which was measured using a laboratory standard method:14 after oral hydration with four and six glasses of water, patients received a non-radiolabeled iothalamate subcutaneous injection (Conray ®); after a one-hour balance period, the patient urinated, the first sample was taken and urinary collection was started. An ultrasound was performed in order to verify complete emptying of the bladder: no patient had urinary retention. After urine collection (approximately 45 to 60 minutes), a second sample was obtained. GFR was calculated with the clearance equation: VIoU/IoP Where: V = urinary flow IoU = iothalamate urinary concentration IoP = iothalamate plasma concentration The mean of the two serum samples and a urinary sample for iothalamate via capillary electrophoresis was used. All GFR measurements were standardized for 1.73 m2 of body surface area, multiplying by 1.73 and dividing by body surface area. GFR was estimated with four equations that use serum creatinine and two equations that use cystatin C with creatinine (Table 1)10,12,13,15-17 The equations are expressed in mL/minute/1.73 m2 and were adjusted multiplying the value by 1.73 and dividing by patient body surface area estimated with the DuBois formula. Statistical analysis Categorical variables are reported as frequencies and percentages and continuous variables as minimum-maximum. Bias was assessed as the median differences between measured glomerular filtration rate (mGFR, measured with iothalamate) and estimated glomerular filtration rate (eGFR, estimated with each one of the equations). Precision was defined as the interquartile range of the differences (IQRd; mGFR-eGFR). Accuracy is expressed as the percentage of estimated measurements (eGFR) within 30 % of mGFR (P30). The best formula was defined as that with less bias, less IQRd (or better precision) and higher P30. Graphs were plotted comparing eGFR with the difference (mGFR-eGFR), with quantile regression lines and lines showing the 95 % confidence interval (using the smoothing function in R). The confidence intervals were obtained with 1000 (...truncated)