Evaluation of the accuracy of Bio-impedance in predicting creatinine clearance in ICU patients with acute kidney injury; Comparison with measured creatinine clearance and calculated by formulas

Introduction: It is still of top priority to find a method to measure creatinine clearance (CrCl) in patients with acute kidney injury (AKI) to regulate drug dosage and avoid treatment failure. Therefore, this study designed to compare CrCl calculated with 6-hour urine output, by formulas, and obtained with the bio-impedance method in patients with AKI hospitalized in ICU. Materials and Methods: In this prospective cross-sectional study, 28 adult patients with an increase in serum creatinine of at least 0.3 according to AKIN criteria and admitted in ICU of Imam Hussein Hospital were selected as the study samples. CrCl was calculated by 6-hour urine output collection, through electrical bio-impedance method, and formulas of Cockcroft and Gault, MDRD, and CKD-EPI. After the required data were collected, they were recorded in pre-prepared checklists, and finally fed into software to be statistically analyzed. Lastly, the obtained CrCl values were compared with those measured by 6-hour urine collection to determine the best formula or method to determine CrCl in patients with AKI. Results: The results showed that the bias values of bio-impedance compared to 6-hour urinary clearance, MDRD, Cockcroft, and CKD-EPI formulas were 6.34, 3.31, 5.01, and 15.14, respectively. Also, error values of bio-impedance compared to 6-hour urinary clearance, MDRD, Cockcroft, and CKD-EPI were respectively 140%, 28%, 60%, and 47%. The internal consistency of the bio- impedance values by the above methods were 0.782, 0.983, 0.939, and 0.893, respectively. Conclusion: According to the obtained results, it can be concluded that none of the formulas listed, including MDRD, Cockcroft, and Gault, and CKD-EPI could predict the CrCl correctly compared to 6-hour urine collection as standard. Also, estimated glomerular filtration rate (GFR) by bio- impedance did not reveal acceptable correlation with 6-hour urine collection. Therefore, this group of patients needs a more precise and specific method(s) to determine the CrCl and GFR.