Comparison of glomerular filtration rate determined by use of single-slice dynamic computed tomography and scintigraphy in cats

Schmidt DM, Scrivani PV, Dykes NL, et al.

Am J Vet Res 2012;73:463-469.

Objective-To compare estimation of glomerular filtration rate determined via conventional methods (ie, scintigraphy and plasma clearance of technetium Tc 99m pentetate) and dynamic single-slice computed tomography (CT). Animals-8 healthy adult cats. Procedures-Scintigraphy, plasma clearance testing, and dynamic CT were performed on each cat on the same day; order of examinations was randomized. Separate observers performed GFR calculations for scintigraphy, plasma clearance testing, or dynamic CT. Methods were compared via Bland-Altman plots and considered interchangeable and acceptable when the 95% limits of agreement (mean difference between methods +/- 1.96 SD of the differences) were </= 0.7 mL/min/kg. Results-Global GFR differed < 0.7 mL/min/kg in 5 of 8 cats when comparing plasma clearance testing and dynamic CT; the limits of agreement were 1.4 and -1.7 mL/min/kg. The mean +/- SD difference was -0.2 +/- 0.8 mL/min/kg, and the maximum difference was 1.6 mL/min/kg. The mean +/- SD difference (absolute value) for percentage filtration by individual kidneys was 2.4 +/- 10.5% when comparing scintigraphy and dynamic CT; the maximum difference was 20%, and the limits of agreement were 18% and 23% (absolute value). Conclusions and Clinical Relevance-GFR estimation via dynamic CT exceeded the definition for acceptable clinical use, compared with results for conventional methods, which was likely attributable to sample size and preventable technical complications. Because 5 of 8 cats had comparable values between methods, further investigation of dynamic CT in a larger sample population with a wide range of GFR values should be performed.