The modification of the measuring method of glomerular filtration rate with dynamic renal imaging by Gates' method

Objective A new glomerular filtration rate (GFR) estimation formula is obtained and verified with the purpose of assessing the feasibility to improve the GFR measuring method with Gates' method. Method A total of 229 adult patients with chronic kidney disease (CKD) were included From September 2011 to March 2016 in the Third Affitiated Hospital of Sunoyat-sen univesity. The GFR were routinely measured by Gates' method (marked as gGFR), and dual plasma sampling clearance method was used to measure the GFR in these patients (marked as rGFR). Taking rGFR as the standard, all the patients with CKD were divided into different stages according to the KDIGO guidelines. Patients were stratified through random sampling basing on their stage, being divided into two groups. Taking the bilateral renal uptake rate of patients by the method of dynamic renal imaging in group A as the independent variables, rGFR as the dependent variables to do the regression analysis, so as to find the best-fitting curve, and achieve a new GFR estimate formula. The new formula was applied to group B for estimation of GFR. Compared the result of GFR in group B with rGFR by paired t test, spearman rank correlation analysis, Bland-Altman consistency evaluation and comparing accuracy. Results The new best-fitting curve equations were applied to group B, we got the new data of GFR (the simple equation results marked as GFRl, the results of the cubic equation marked as GFRc). GFRl, GFRc, gGFR were closely related to rGFR (P<0.01). GFRl and GFRc best correlated with rGFR (r=0.885). Consistency analysis demonstrated that deviation, absolute deviation and limit of agreement of GFRc was lowest among GFRl, GFRc, gGFR and best consist with rGFR, followed by GFRl and gGFR. The limit of agreementof gGFR was out of the pre-set professional cut-off points: 60 ml·(min·1.73 m2)-1. In the term of accuracy analysis, GFRl showed highest concordance with rGFR±30%, and followed by GFRc. The 30% accuracy of GFRl and GFRc were both more than 70% while that of gGFR was less than 70%. Significant differences were also found in GFRl vs. gGFR, and GFRc vs. gGFR, respectively (P<0.01). Conclusion The new fitting formulas have better consistency and correlation with dual plasma sampling method, while compared with Gates' method, the accuracy of the new fitting formulas is superior to Gates' formula. The new fitting formula can improve the performance of Gates'method.The cubic fitting formula was better potential inpredicting GFR than the linear one. Key words: Chronic kidney disease(CKD); Glomerular filtration rate(GFR); Radioisotope renography; Dual plasma sampling clearance