Evaluation Of GFR Estimating Equations In Type 2 Diabetes

Background and ObjectiveRecently,the incidence of diabetes is fast increasing due to the developing of economy and the prolongation of average life.Diabetic nephropathy(DN)has become one of the main causes of end stage renal failure.Thus it is very necessary to perform early GFR estimating in order to detect and treat DN in time.24-hour endogenous creatnine clearance(Ccr)once widely used is not the best choice to evaluate renal function,because of its poor repetitiveness which partly caused by its complicated procedure and bad compliance.At the same time generalization of ^99mTc-diethlene triamine pentaacetic acid(^99mTc—DTPA)dynamic kidney imaging is hindered by the present economy.So GFR estimating equations basing on serum creatinine(Scr)attract peoples' attention.The use-value of estimators(Cockcroft-Gault formula,abbrevisted MDRD equation,MDRD-7 equation)of the true glomerular filtration rate(eGFR)in Type 2 diabetes still remains to be studied,though that has been proved in chronic renal failure patients.The aim of this study is to analyze use-value of eGFR and Ccr in Type 2 diabetes comparing with nondiabetes,to offer optimal renal function appraisal method for T2DM.Subjects and Methods1.SubjectsNinety four Type 2 diabetes(according with WHO diagnostic criteria for Type 2 diabetes set in 1995)without clinic hypertensive nephropathy from Sir Run Run Shaw Affiliated Hospital of Zhejiang University between March 2007 to February 2008 severed as T2DM group in this study.There were 55 male and 39 female cases,with the average age of 56±13,average diabetic duration of 6.54±5.9 years. There were 41(43.6%)with hypertension(according with WHO diagnostic criteria for hypertension),48(51.1%)with metabolic syndrome(according with IDF diagnostic criteria for metabolic syndrome).At the same time fifty five chronic renal disease patients(according with American NKF-K/DOQI criteria for chronic renal disease)without diabetes severed as NDM group.There were 29 male and 26 female cases,with the average age of 50±13,23(41.8%)with hypertension, 31(56.4%)with renal biopsy and pathologic diagnosis.The two groups were divided into hypertension subgroup and normal subgroup and T2DM was divided into normal subgroups and abnormal subgroups according to metabolic syndrome,hypoalbuminemia and Scr.Basing on urinary albumin excretion T2DM was divided into normal albuminuria(NAU,UAE＜30mg/24h), micro albuminuria(MAU,30mg/24h≤UAE＜300mg/24h)and clinical albuminuria (CAU,UAE≥300mg/24h).Finally the GFR of two groups was divided into four levels,according to NKF-K/DOQI guideline:Stage-1 GFR≥90ml/min/1.73m²;Stage-2 60≤GFR＜90ml/min/1.73m²;Stage-3 30≤GFR＜60 ml/min/1.73m²;Stage-4 GFR＜30ml/min/1.73m².2.Methods2.1 General clinical informationAge,gender,history,course of diabetes,smoking history,alcohol drinking history were recorded and weight,height,systolic blood pressure(SBP),diastolic blood pressure(DBP),waistline were measured(Nondiabetes did not receive waistline measure).T2DM did digital measuring of blood sugar on admission and body mass index(BMI)was calculated for all the patients.2.2 Measurement of biochemical indicatorsAfter three days of vegetarian diet without tea,coffea and heavy exercise,the urine was collected with methylbenzol for 24 hours.Scr,serum albumin(ALB) triglyceride(TG),total cholesterol(TC),high density Iipoprotein(HDL-C),low density lipoprotein(LDL-C),fasting blood sugar(FBS),blood urea nitrogen(BUN), urinary creatinine,glycosylated hemoglobin(HbAlc)and urine albumin were tested by the clinical laboratory of the hospital at the time when urine collecting was finished(Nondiabetes did not the last two tests).2.3 Measurement of GFR,calculation of GFR estimating equations and CcrAll subjects received ^99mTc—DTPA dynamic kidney imaging and GFR estimating(eGFR)according to the formula of Cockcroft -Gault formula, abbrevisted MDRD equation and MDRD-7 equation,but Ccr was only calculated in T2DM.3.StatisticsThe datas were analyzed by software SPSS13.0.Normal datas were expressed as mean±SD,non-normal datas were expressed as median(range)and categorical variable datas were expressed as%.Three or four groups were compared using single-factor analysis of variances,and the difference of intra-group in two groups was analyzed by independent samples t test.Rank sun test and x² test were used in analysis of heterogeneity variance and rates.Diagnostic significance was evaluated by ROC curve.Correlation were evaluated by Pearson correlation coefficients.Statistical significance was defined as P＜0.05.Results1.Comparison of eGFRs,Ccr and GFRThere were 45 patients at Stage-1(GFR≥90ml/min/1.73m²),31at Stage-2(60≤GFR＜90ml/min/1.73m²),11 at Stage-3(30≤GFR＜60ml/min/1.73m²),7 at Stage-4(GFR＜30 ml/min/1.73m²)in T2DM and there were 15,10,20,10 in NDM.There was no significant difference between the eGFRs and GFR in both T2DM and NDM,no matter what the level of GFR is.But there was significant difference between Ccr(75.92±8.88 ml/min/1.73m²)and GFR(87.94±28.88 ml/min/1.73m²),CG-eGFR(74.45±16.80 ml/min/1.73m²)in T2DM(P＜0.05). 2.Pearson correlation analysis between eGFRs/Ccr and GFRThere was a significant correlation between eGFRs and GFR in T2DM,CG formula(r=0.76,P=0.003),MDRD formula(r=0.79,P=0.001),MDRD-7 formula(r=0.79,P=0.004).Though there was a significant correlation between Ccr and GFR(r=0.79,P=0.005),it was inferior to that between eGFRs and GFR in correlation intensity.And in NDM,CG formula(r=0.76,P=0.003),MDRD formula(r=0.80,P=0.005),MDRD-7 formula(r=0.79,P=0.005)also showed positive correlation with GFR.3.The areas under ROC curve of eGFRs and CcrThe areas under ROC curve of Cockcroft -Gault formula,abbrevisted MDRD equation and MDRD-7 equation in T2DM were all larger than 0.8 with average areas of 0.892,0.853,0.839,0.853 for different GFR levels,and earea of CG is significant larger than Ccr's(0.767)at Stage 1-2.The areas of the three eGFRs of different formulas showed no difference in both T2DM and NDM.4.Different blood pressure,gender,UAE,plasma albumin,Scr,metabolic state did not effect the accuracy of GFR estimating equations in T2DM.5.Age,high level of HbAlc and UAE were independent risk factors of GFR decline in T2DM.ConclusionGFR estimating equations might take the place of ^99mTc—DTPA dynamic kidney imaging in clinic screening of diabetic nephropathy and it is superior to Ccr.