Evaluation of the Accuracy of Standard Renal Function Equations in Critically Ill Patients with Subarachnoid Hemorrhage

Background: Obtaining an accurate estimation of renal function is germane to optimizing care in critically ill patients. However, there is no consensus on the most accurate renal function assessment to utilize in this patient population, particularly in aneurysmal subarachnoid hemorrhage (aSAH) patients. Thus, the objective of this observational study was to determine the comparability of renal function equations to body surface area (BSA)-adjusted 8-h creatinine clearance (CrCl) in aSAH patients. Methods: A PubMed search investigated the applicability of various renal function equations in critically ill patient populations. A subset of these equations was compared to BSA-adjusted 8-h CrCl from a previous study with aSAH patients with no evidence of renal dysfunction (admission serum creatinine < 1.5 mg/dL) and no history of chronic kidney disease. Area-under-the-curve (AUC) calculations were completed using serial laboratory measurements to validate preliminary findings. Results: A total of 14 renal function equations were identified with seven carried forward for further analysis based upon a priori criteria. Seven equations were excluded for various reasons, including lack of available clinical data, redundancy with other equations, and dissimilar patient populations to this study. When directly compared to the BSA-adjusted 8-h CrCl, only the Cockcroft-Gault and BSA-adjusted Cockcroft-Gault equations were not statistically significantly different (P = 0.0886 and P = 0.4805, respectively); all other equations were statistically significantly different (P < 0.0001). Additionally, only 52% and 44% of patients had average values within 20% of the BSA-adjusted 8-h CrCl using the Cockcroft-Gault and BSA-adjusted Cockcroft-Gault equations, respectively. Finally, the AUC calculations corroborated the preliminary findings with similar results in statistical testing for the Cockcroft-Gault and BSA-adjusted Cockcroft-Gault (P = 0.6300 and P = 0.1513, respectively). Conclusions: The Cockcroft-Gault equation may be the best renal function equation to assess in critically ill patients diagnosed with aSAH. However, accuracy and consistency in assessing renal function when compared to the BSA-adjusted 8-h CrCl were lacking. Thus, this study suggests the BSA-adjusted 8-h CrCl may be the most appropriate assessment of renal function in patients with aSAH.