Comparison Of GFR Equations In Patients With Chronic Kidney Disease

Objective Serum creatinine may not reflect glomerular filtration rate (GFR) in the early stages of chronic kidney disease (CKD).Serum cystatin C (cysC), however, has the potential to more accurately determine early GFR reduction. We Compared the GFR equations in patients with chronic kidney disease, estimating GFR using serum creatinine alone,serum cystatin C alone and in combination with serum creatinine. The purpose is to find an accurate, precise,economic, and convenient equation for estimation of glomerular filtration rate in patients with chronic kidney disease,especially in the early stages of chronic kidney disease.Methods We derived a reference GFR by using 99mTc-DTPA clearance in a cohort of 119 adult hospitalized patients with CKD,collected from January in 2008 to January in 2009. Serum cystatin C(CysC) concentration was determined by particle-enhanced nephelometric immunoassay (PENIA), Serum creatinine (SCr) by alkaline trinitrophenal method for every patient. Estimation of glomerular filtration rate were calculated from five acceted calculations:eGFR1 =86×CysC-1.132;eGFR2 =176×Scr-0.607×CysC-0.638×Age-0.171(Female×0.85);eGFR3 =175×Scr-1.234×Age-0.179(Female×0.79);eGFR4 ={(86×CysC-1.132)×[175×Scr-1.234×Age-0.179(Female×0.79)]}-1/2;eGFR5 =169×Scr-0.608×CysC-0.63×Age-0.157(Female×0.83).We compared reference values with estimated GFR values and furthermore applied regression analysis method and Bland-Altman plot to one equation based solely on cysC, and to another combined SCr and cysC .Results We got five regression equations: rGFR=0.603×eGFR1+18.66 (r=0.862 , P<0.001);rGFR =0.491×eGFR2+24.16 (r=0.879 , P<0.001); rGFR=0.417×eGFR3+28.97 (r=0.837,P<0.001);rGFR=0.554×eGFR4+20.92 (r=0.88,P<0.001);rGFR =0.488×eGFR5+23.84 (r=0.88,P<0.001) (r=0.88,P<0.001).The five correlation coefficient values (r =0.84,0.88,0.86,0.88,0.88, respectively) all are higher than 0.8.We know that eGFRs have good correlation with rGFR .The difference, precision, and accuracy of the estimate GFR derived from combined cysC and modified MDRD calculation,were better than that from other calculations (P<0.001,respectively),especially the modified Modification of Diet in Renal Disease (MDRD).The stage misclassification of CKD by eGFR1, eGFR2,eGFR3, eGFR4 and eGFR5 was compared. In CKD stage 2 ,3 eGFR1 showed smaller percent of CKD stage misclassification compared with eGFR3 (48.7%,53.8% and 53.8%,64.1%,respectively,χ2-test, P<0.001). Compared with serum creatinine, serum cystatin C can optimize early detection for Chronic kidney patients. Conclusion 1. Serum cystatin C is an accurate, precise,and reliable marker of glomerular filtration rate in patients with chronic kidney disease. 2.The estimated GFR combining cysC and SCr is the more accurately matched the reference GFR than the others,which using serum creatinine alone,serum cystatin C alone.3.The estimated GFR combining cysC and modified MDRD calculation is the most accurately matched the reference GFR at all stages of CKD than the other equations, particularly in patients with near-normal kidney function.