Evaluation of the Glomerular Filtration Rate in AKI by Kinetic Estimated Glomerular Filtration Rate in a Tertiary Referral Hospital in Mexico

Background: Estimating glomerular filtration rate (GFR) in acute kidney injury (AKI) is problematic as plasma creatinine changes rapidly. There is no widely accepted method for estimating renal function in AKI. Kinetic estimated GFR formula and creatinine clearance is an estimate of immediate biomarker clearance derived from two discrete measurements that may better represent the acute function. However, neither the kinetic GFR formula nor the four-hour creatinine clearance have been evaluated in the Mexican population. Methods: Prospective, analytical study, in patients with acute kidney injury outside of critical care unit. Urinary creatinine clearance was performed along with the calculation of GFR using the kinetic estimated GFR formula and the 2021 CKD-EPI formula with creatinine-cystatin C. Results: Data were analyzed for 68 patients with a mean age of 67.21 years, 61% were male, and 47% of patients had chronic kidney disease. The mean baseline creatinine was 1.4 mg/dl and the mean GFR was 65.85 mg/dl. The main aetiological factor for AKI was sepsis (33%), followed by cardiorenal syndrome. A Pearson correlation of 0.80 (p= 3.19e-16 CI 95 0.70-0.87) was found between the kinetic estimated GFR formula and four-hour creatinine clearance; concordance was analyzed by the Bland-Altman method with a mean difference of -0.14 with upper LoA of 21.10 (CI 95 16.4-25.7) and lower LoA -21.40 (CI 95 -26.0 -16.7). However, the concordance for the formula kinetic estimated GFR and 2021 CKD-EPI cystatin formula was 0.33. Conclusion: In Mexican patients with AKI, there is no standardization for GFR calculation. However, with creatinine determinations, GFR can be estimated using the kinetic estimated GFR formula, although it can also be evaluated by 4-hour creatinine clearance, which showed statistical concordance. Evaluation of GFR in AKI with cystatin did not correlate well with either the kinetic estimated GFR formula or the 4-hour creatinine clearance.