New Predictive Equations Improve Monitoring of Kidney Function in Patients With Diabetes MARIE-CHRISTINE BEAUVIEUX, PHD 1 FRANC ¸ OISE LE MOIGNE, PD 1 CATHERINE LASSEUR, MD 2 CHRISTELLE RAFFAITIN, MD 2 CAROLINE PERLEMOINE, MD 3 NICOLE BARTHE, PD 4 PHILIPPE CHAUVEAU, MD 2 CHRISTIAN COMBE, PHD 2 HENRI GIN, PHD 3 VINCENT RIGALLEAU, PHD 3 OBJECTIVE — The Cockcroft-Gault and Modification of Diet in Renal Disease (MDRD) equations poorly predict glomerular filtration rate (GFR) decline in diabetic patients. We sought to discover whether new equations based on serum creatinine (the Mayo Clinic Quadratic [MCQ] or reexpressed MDRD equations) or four cystatin C– based equations (glomerular filtra- tion rate estimated via cystatin formula [Cys-eGFR]) were less biased and better predicted GFR changes. RESEARCH DESIGN AND METHODS — In 124 diabetic patients with a large range of isotopic GFR (iGFR) (56.1  35.3 ml/min per 1.73 m 2 [range 5–164]), we compared the performances of the equations before and after categorization in GFR tertiles. A total of 20 patients had a second determination 2 years later. RESULTS — The Cockcroft-Gault equation was the least precise. The MDRD equation was the most precise but the most biased according to the Bland-Altman procedure. By contrast with the MDRD and, to a lesser extent, the MCQ, three of the four Cys-eGFRs were not biased. All equations overestimated the low GFRs, whereas only the MDRD and Rule’s Cys-eGFR equations underestimated the high GFRs. For the subjects studied twice, iGFR changed by -8.5  17.9 ml/min per 1.73 m 2 . GFR changes estimated by the Cockcroft-Gault (-4.5  6.8) and MDRD (-5.7  6.2) equations did not correlate with the isotopic changes, whereas new equation- predicted changes did: MCQ: -8.7  9.4 (r = 0.44, P  0.05) and all four Cys-eGFRs: -6.2  7.4 to -7.3  8.4 (r = 0.60 to 0.62, all P  0.005), such as 100/cystatin-C (r = 0.61, P  0.005). CONCLUSIONS — The new predictive equations better estimate GFR than the Cockcroft- Gault equation. Although the MDRD equation remains the most accurate, it poorly predicts GFR decline, as it overestimates low and underestimates high GFRs. This bias is lesser with the MCQ and Cys-eGFR equations, so they better predict GFR changes. Diabetes Care 30:1988–1994, 2007 C hronic kidney disease (CKD) is a major health problem worldwide, with dramatically rising incidence and prevalence. Patients with diabetes are particularly affected by this negative de- velopment. It is necessary to stratify CKD and estimate its progression because dia- betes is the leading cause of end-stage re- nal disease (1). The National Kidney Foundation guidelines recommend esti- mating glomerular filtration rate (GFR) in subjects with CKD (2). According to the National Kidney Foundation and the American Diabetes Association, GFR can be estimated in adults by using the Cock- croft-Gault or the Modification of Diet in Renal Disease (MDRD) equations (1,3). Neither of these equations, based on se- rum creatinine, is highly predictive of GFR. The Cockcroft-Gault equation is less accurate (4), biased by body weight (5), and less robust in patients with poor glycemic control (6). The simplified MDRD equation allows renal function to be classified with acceptable precision and requires only usual information about the patient. However, adjustment may be required to avoid error due to creatinine assays and calibrators (7). Moreover, the MDRD is known to under- estimate high or normal GFR, leading to dramatic inaccuracy, as evidenced in the Diabetes Control and Complications Trial cohort (8). Only 70% of subjects overall may be considered well stratified, accord- ing to the Kidney Disease Outcomes Quality Initiative, with these equations (9). Their precision seems even worse for estimating CKD progression, leading to unacceptable inaccuracy (10). The esti- mated equations reflected the measured GFR decline only in the most advanced (Kidney Disease Outcomes Quality Initia- tive stage 3) cases (11), suggesting that variable predictive performance due to GFR level may play a role in this imprecision. New predictive equations therefore need to be developed and validated. They could be based on the results of serum creatinine in subjects with (as in the MDRD) or without renal impairment. The Mayo Clinic Quadratic (MCQ) equation was established this way (12). Another means of measurement is to include the ●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●● From the 1 Biochemistry Laboratory, Ho ˆ pital Haut-Le ´ve ˆ que, Pessac, France; 2 Nephrology, Ho ˆ pital Pellegrin, Place Ame ´ lie Raba-Le ´ on, Bordeaux, France; 3 Nutrition and Diabetes, Ho ˆ pital Haut-Le ´ve ˆ que, Pessac, France; and the 4 Nuclear Medicine Laboratory, Ho ˆ pital Haut-Le ´ve ˆque, Pessac, France. Address correspondence and reprint requests to Marie-Christine Beauvieux, Laboratoire de Biochimie, Ho ˆ pital Haut-Le ´ve ˆque, Avenue de Magellan, 33604 Bordeaux Cedex, France. E-mail: marie- christine.beauvieux@chu-bordeaux.fr. Received for publication 31 December 2006 and accepted in revised form 13 May 2007. DOI: 10.2337/ dc06-2637. Additional information for this article can be found in an online appendix at http://dx.doi.org/10.2337/ dc06-2637. Abbreviations: CKD, chronic kidney disease; Cys-eGFR, glomerular filtration rate estimated via cystatin formula; GFR, glomerular filtration rate; iGFR, isotopic GFR; MCQ, Mayo Clinic Quadratic; MDRD, Mod- ification of Diet in Renal Disease; rMDRD, reexpressed MDRD; ROC, receiver-operating characteristic. A table elsewhere in this issue shows conventional and Syste `me International (SI) units and conversion factors for many substances. © 2007 by the American Diabetes Association. The costs of publication of this article were defrayed in part by the payment of page charges. This article must therefore be hereby marked “advertisement” in accordance with 18 U.S.C. Section 1734 solely to indicate this fact. Clinical Care/Education/Nutrition/Psychosocial Research O R I G I N A L A R T I C L E 1988 DIABETES CARE, VOLUME 30, NUMBER 8, AUGUST 2007 Downloaded from http://diabetesjournals.org/care/article-pdf/30/8/1988/596552/zdc00807001988.pdf by guest on 17 June 2022