A rapid simplified method for the estimation of glomerular filtration rate (GFR)

Abstract

2007

Objectives: To determine whether a simplified method of GFR determination using a renal to background ratio(R/B) can reliably predict GFR non-invasively without patient’s(pts) height, weight, pre-syringe counts and post-syringe counts.

Methods: GFR determinations using 2.0 mCi of Tc-99m DTPA for 56 initial subjects were performed using the Gates Method(GM) which included pre and post syringe counts as well as pts height and weight. Average counts per pixel were determined for each kidney and background region used by the GM. R/B ratios were plotted against the Gates GFR for all 112 kidneys and a least squares fitting of the data performed. Subsequently,26 consecutive test pts then underwent comparisons of the GFR by the GM with the GFR obtained by using the equation generated by the least squares fitting of the initial data set (y=mx+b). The results of the GM were compared to the R/B method using a Students T-test analysis.

Results: The least squares linear relationship yielded an equation of T/B ratio =0.0685 GFR+1.3021(R2 =0.79). Comparison of the GFR calculated by the ratio method compared to the GFR calculated by the GM was analyzed using a T-test comparison.Mean GFR for each kidney for 26 consecutive subjects using the GM was 17.5cc/min(SD=14.1), the mean value for the ratio method was 18.4cc/min(SD=15.1). (P=0.30)indicating no statistically significant difference for GFR between the 2 methods.

Conclusions: Using a simple concept of kidney to background ratios, we were able to demonstrate that the results were concordant with the more complex calculation using the GM. The ratio method is subject to fewer sources of error and are independent of the pt’s height or weight or the pre and post syringe counts.