Comparison of methods for estimating glomerular filtration rate in critically ill patients with acute kidney injury

Background. In critically ill patients with acute kidney injury, estimates of kidney function are used to modify drug dosing, adjust nutritional therapy and provide dialytic support. However, estimating glomerular filtration rate is challenging due to fluctuations in kidney function, creatinine production and fluid balance. We hypothesized that commonly used glomerular filtration rate prediction equations overestimate kidney function in patients with acute kidney injury and that improved estimates could be obtained by methods incorporating changes in creatinine generation and fluid balance. Methods. We analysed data from a multicentre observational study of acute kidney injury in critically ill patients. We identified 12 non-dialysed, non-oliguric patients with consecutive increases in creatinine for at least 3 and up to 7 days who had measurements of urinary creatinine clearance. Glomerular filtration rate was estimated by Cockcroft–Gault, Modification of Diet in Renal Disease, Jelliffe equation and Jelliffe equation with creatinine adjusted for fluid balance (Modified Jelliffe) and compared to measured urinary creatinine clearance. Results. Glomerular filtration rate estimated by Jelliffe and Modification of Diet in Renal Disease equation correlated best with urinary creatinine clearances. Estimated glomerular filtration rate by Cockcroft–Gault, Modification of Diet in Renal Disease and Jelliffe overestimated urinary creatinine clearance was 80%, 33%, 10%, respectively, and Modified Jelliffe underestimated GFR by 2%. Conclusion. In patients with acute kidney injury, glomerular filtration rate estimating equations can be improved by incorporating data on creatinine generation and fluid balance. A better assessment of glomerular filtration rate in acute kidney injury could improve evaluation and management and guide interventions.