Supplementary Material for: Using the Kinetic Estimating Glomerular Filtration Rate Equation for Estimating Glomerular Filtration Rate and Detecting Acute Kidney Injury: A Pilot Study

Background: Estimating the glomerular filtration rate (eGFR) when the creatinine (Cr) is rapidly changing, as in acute kidney injury (AKI), has been a challenge. The Kinetic Estimated Glomerular Filtration Rate (KeGFR) formula by S. Chen estimates the GFR in the acute state by factoring the time interval between rising Cr values and the volume of distribution (V_D). It provides the clinician with an eGFR value for each non-steady state Cr value. We applied the KeGFR formula to detect AKI in an adult non-ICU inpatient setting. We then compared KeGFR with the current standard Acute Kidney Injury Network (AKIN criteria) and Risk Injury Failure Loss End-Stage Kidney Disease (RIFLE criteria) and new criteria (Waikar-Bonventre, Delta check) for AKI detection. Methods: A total of 250 consecutive adult patients admitted to the Medical wards were screened. Patient episodes with a change in Cr of > 4.3% (Biological Variation) were included in the study (n = 80). The KeGFR equation was applied to this cohort after calculating the V_D individually after estimating the initial GFR by using MDRD equation. A fall in KeGFR of 25% or more was considered as AKI. The AKIN, Waikar-Bonventre, RIFLE, and Delta Check criteria were also applied to this cohort and compared with the KeGFR criterion. Clinical adjudication was performed when there was discordance between AKI episodes detected by AKIN and KeGFR criteria. Results: There were 50 episodes of AKI by AKIN classification and 31 episodes by KeGFR criterion. All but 1 (30) episode detected by KeGFR criterion fulfilled the AKI definition by AKIN. AKIN diagnosed an additional 20 episodes. However, all of these had an elevated Cr level on admission; thus, requiring the incorporation of baseline Cr by AKIN which is not part of the KeGFR formula. Five of these 20 patients were deemed as not having AKI by clinical adjudication. All patients with in-hospital AKI and ongoing AKI were detected by both the criteria. The KeGFR criteria detected almost all (24/25) episodes of AKI identified by the Waikar-Bonventre method. The latter method detected 77% (24/31) of the AKI episodes identified by KeGFR. Conclusion: The KeGFR equation can be readily applied to estimate GFR in the non-steady state. A KeGFR-based criterion successfully detected ongoing and in-hospital AKI in this study. Community acquired AKI that did not progress after admission was not detected by the KeGFR criterion.