Comparison Of Four Equations To Estimate The Glomerular Filtration Rate In The Adult Diabetes Population

ObjectiveThe glomerular filtration rate (GFR) is considered as the best overall index of kidney function in health and disease. Recently the 99Tcm-DTPA nephro-dynamic imaging is regarded as the golden standard of evaluating GFR, but it has some disadvantages, such as expensive, complex, time-consuming, radioactive. For these reasons, GFR is always estimated from equations using serum creatinine, age, race, sex and body size. However the study population of these equations is the westen CKD, so we don't know whether these equations are suitable to estimate the renal function of diabetic patients in China. This study is to evaluate the applicability of the C-G equation, the abbreviated Modification of diet in Renal Disease(MDRD)study equation, the improved abbreviated MDRD equation and the CKD-EPI equation to estimate the renal function of diabetic patients in our country.Methods1. Objects: 329 adult patients, who hospitalized in Endocrine and Metabolic Department of Xijing hospital from 2007 to 2009, were all diagnosed according to the WHO diagnosis standard of diabetes defined in 1999. After hospitalization, they took on a check-up for observing 99Tcm-DTPA glomerular filtration rates and drew blood for serum creatinine. Patients with pregnancy, lactation, acute renal failure, severe malnourishment, deficiency of skeletal limb, ketoacidosis, dehydration, congestive heart failure, hydropneumonia and the use of aspirin, nonsteroidal anti-inflammatory drugs, cimetidine, ranitidine drugs before 48 hours of the test were excluded.2. The equations (sGFR ml·min-1·(1.73m2 ) -1)(1) The C-G equation: First, estimate Ccr: Ccr(ml·min)=[140-age(years)]×weight (kg)×Scr(mg/d1)-1×72-1(×0.85 if female), multiplied by 0.84 is GFR; Second, calculate BSA: BSA(m2)=0.007184×weight (kg)0.425×Height(cm)0.725. Last, calculate GFR: GFR=Ccr×0.84×1.73/BSA, the results have been adjusted for body surface area (BSA).(2) The abbreviated MDRD equation: GFR=186×Scr(mg/dl)-1.154×age(years)-0.203(×0.742 if female)(3) The improved abbreviated MDRD equation: GFR =175×Scr(mg/dl)-1.234×age(years)-0.179(×0.79 if female)(4)The CKD-EPI equation: GFR=141×min(Scr(mg/dl)/k,1)α×max(Scr(mg/dl)/ k,1)-1.209×0.993years×1.018(if female)×1.159 (if black), where Scr is serum creatinine, k is 0.7 for females and 0.9 for males,αis -0.329 for females and -0.411 for males, min indicates the minimum of Scr/k or 1, and max indicates the maximum of Scr/k or 1.3.Protocols: Patients were divided into two groups according to GFR (ml·min-1·(1.73m2 ) -1) levels that defined by NKF-K/DOQI(The National Kidney Foundation Kidney Disease Outcomes Quality Initiative): 256 cases in group 1 (GFR≥60ml·min-1·(1.73m2)-1), 74 cases in group 2 (GFR<60 ml·min-1·(1.73m2)-1). Renal inadequacy was defined as GFR<60 ml·min-1·(1.73m2 ) -1.4. Statistical analysis: paired t-test, correlation analysis, agreement test and ROC curve analysis were applied to evaluate the statistical significance of differences among the four equations in this study.Results1. Comparisons of estimated GFR and sGFR (gold standard): The results of the four equations obviously deviated from the GFR measured by 99Tcm-DTPA dynamic renal Imaging.①In group 1(GFR≥60 ml·min-1·(1.73m2)-1), the results of the four equations obviously underestimate the real GFR. Among them, the improved abbreviated MDRD equation is the best;②In group 2(GFR≥60 ml·min-1·(1.73m2)-1), the results of the four equations overestimate the real GFR. Compared with other three, GFRCKD-EPI is better;③totally, the improved abbreviated MDRD equation is the best.2. Correlation analysis:The four estimated GFR is correlated with sGFR significantly (P<0.001), and the correlation between the GFR estimated by the abbreviated MDRD equation, the improved abbreviated MDRD equation and the sGFR is higher in GFR≥60ml·min-1·(1.73m2)-1 group than in GFR<60ml·min-1·(1.73m2)-1 group. In all patients, the correlation between the improved abbreviated MDRD equation and sGFR is the highest compared with others.when renal inadequacy was defined as GFR<60ml·min-1·(1.73m2)-1, consistency check were done to compare the four equtions, the C-G equation, the abbreviated MDRD equation, the improved abbreviated MDRD equation and the CKD-EPI equation'Kappa value respectively were 0.297,0.522,0.514,0.269(P<0.001). So the conclusion could be drawn: the consistency of the abbreviated MDRD equation, the improved abbreviated MDRD equation is better than the C-G equation and the abbreviated MDRD equation.3. Comparison of the potence in classifying renal function of estimated GFR and sGFR:In this population, the proportion of renal inadequacy in GFRCG, GFRMDRD, GFRimproved MDRD, GFRCKD-EPI and sGFR were 41.64%, 26.14%, 21.58%, 43.77% and 22.49% respectively. The morbidity of renal inadequacy from GFR improved MDRD is the closest with sGFR's compared with other three.4. Accuracy by receiver operating characteristic curve analysis:When GFR<60ml·min-1·(1.73m2)-1 is golden standard of renal inadequacy, we evaluate the sensitivity and the specificity of these four equations. The order of sensitivity: GFRCG=GFRCKD-EPI > GFRMDRD > GFRimproved MDRD(71.6% VS 71.6% VS 68.9% VS 59.5%). The order of specificity: GFR improved MDRD>GFRMDR>GFRCG>GFRCKD-EPI(89.8% VS 86.3% VS 67.5% VS 64.3%). Areas under ROC curves of GFRCG, GFRMDRD, GFRimproved MDRD and GFRCKD-EPI were 0.787, 0.849, 0.851, 0.781 respectively. When renal inadequacy was defined GFR<60ml·min-1·(1.73m2)-1 the accuracy of the improved abbreviated MDRD equation is higher than the other equetions.ConclusionsIn estimating the GFR of diabetic patients in China: when GFR≥60 ml·min-1·(1.73m2) -1, the results of the four equations obviously underestimate the real GFR; when GFR<60ml·min-1·(1.73m2)-1, the results of the four equations overestimate the real GFR. In all patients, the improved abbreviated MDRD equation is better than the others.