Comparing Cystatin C Estimated GFR With Creatinine Estimated GFR in Acute Kidney Injury Recovery

Current guidelines recommend creatinine-based estimated glomerular filtration rate (eGFRcr) to assess kidney recovery after acute kidney injury (AKI); however, this may be inaccurate because of loss of muscle mass. Cystatin C-based eGFR (eGFRcys) is an alternative that is not similarly affected. In addition, simple calculations (e.g., creatinine muscle index, CMI) incorporating the difference between eGFRcr and eGFRcys may indicate prognosis. We sought to determine whether eGFRcr differs from eGFRcys after AKI and whether CMI is associated with mortality.

The AKI Risk in Derby (ARID) study is a prospective parallel-group cohort study. Hospitalized participants with and without exposure to AKI were matched 1:1 for age, baseline kidney function, and diabetes. eGFRcr and eGFRcys at 3 months after admission were compared in 849 participants. Associations between CMI and outcomes, including mortality, heart failure, and hospitalization were assessed at 5 years.

eGFRcys was lower than eGFRcr (53.4, [interquartile range, IQR: 34.3-85.5] vs. 68.4 [IQR: 52.5-84.7] ml/min per 1.73 m², P < 0.001), with more pronounced differences in those with AKI. eGFRcys categorized more participants with chronic kidney disease (CKD) (in AKI group: eGFRcr < 60 ml/min per 1.73 m² in 44.9%; eGFRcys < 60 ml/min per 1.73 m² in 69.6%, P < 0.001). In the AKI group, higher CMI was independently associated with lower mortality at 5 years (adjusted hazard ratio: 0.931 [0.874-0.992] mg/d per 1.73 m², P = 0.03).

There are significant differences at 3 months after AKI in eGFR derived from creatinine versus cystatin C. The magnitude of difference between these estimates is associated with subsequent mortality. Further research is required to determine the optimal approach to patient assessment after AKI.