Role of Loop Diuretic Challenge in Stage 3 Acute Kidney Injury

Abstract

The furosemide stress test, by assessing the proximal tubular cells' ability to transport it to its site of action, is able to predict the progression AKI to higher stages.10 More recently, the response to loop diuretics has also been evaluated to predict progression to AKI after cardiac surgery,11 to predict progression of AKI when stratified according to biomarkers,12 and to select patients for early initiations of dialysis.13 However, the capability of a loop diuretic challenge test to predict the need for dialysis among those with AKI stage 3 has not been evaluated. Because patients with stage 3 AKI are at risk for complications that could necessitate urgent dialysis, we designed this study to assess whether the increase in urine output following the loop diuretic challenge can be utilized to predict the need for dialysis within 24 hours in patients with predialysis stage 3 AKI. Statistical Analyses We used the t test and Wilcoxon rank sum test as appropriate to compare differences in baseline variables. Because the 2-hour urine output after loop diuretic challenge has been reported to have the best performance for the prediction of AKI stages 1 and 2 progression10 and 6-hour urine output has been found to have the best ability for prediction of delayed graft function in patients with kidney transplant,17 we compared the area under the receiver operating characteristic curve (AUC) of both 2-hour and 6-hour urine outputs to predict the need for dialysis within the next 24 hours and 72 hours. Because of the nonlinear relationship between post-loop diuretic challenge urine output and need for urgent dialysis, we used restricted cubic spline transformations of the post-loop diuretic challenge urine output for the analyses. Because of the substantial protein binding of loop diuretics, rather than being filtered through the glomeruli, these drugs are actively secreted by the probenecidsensitive organic anion transporters in the proximal tubular cells.