Cystatin C or creatinine for pre-operative assessment of kidney function and risk of post-operative acute kidney injury: a secondary analysis of the METS cohort study

Abstract

Background Post-operative acute kidney injury (PO-AKI) is a common surgical complication consistently associated with subsequent morbidity and mortality. Prior kidney dysfunction is a major risk factor for PO-AKI, however it is unclear if serum creatinine, the conventional kidney function marker, is optimal in this population. Serum Cystatin C is a kidney function marker less affected by body composition and might provide better prognostic information in surgical patients. Methods Pre-defined, secondary analysis of a multi-centre prospective cohort study of preoperative functional capacity. Participants were aged ≥ 40 years undergoing non-cardiac surgery. We assessed the association of pre-operative estimated glomerular filtration rate (eGFR) calculated using both serum creatinine and serum Cystatin C with PO-AKI within three days after surgery, defined by KDIGO creatinine changes. The adjusted analysis accounted for established AKI risk factors. Results 1347 participants were included (median age 65 years, interquartile range 56–71) of whom 775 (58%) were male. A total of 82/1347 (6%) patients developed PO-AKI. These patients were older, had higher prevalence of cardiovascular disease and related medication, were more likely to have intra-abdominal procedures, had more intraoperative transfusion, and were more likely to be dead at one year after surgery 6/82 (7.3%) vs 33/1265 (2.7%), P = 0.038. Pre-operative eGFR was lower in AKI than non-AKI patients using both Creatine and Cystatin C. When both measurements were considered in a single age and sex adjusted model, eGFR-Cysc was strongly associated with PO-AKI, with increasing risk of AKI as eGFR-Cysc decreased below 90, while eGFR-Cr was no longer significantly associated. Conclusions Data from over 1000 prospectively recruited surgical patients confirms pre-operative kidney function as major risk-factor for PO-AKI. Of the kidney function markers available, compared to Creatinine Cystatin C had greater strength of association with PO-AKI and merits further assessment in pre-operative assessment of surgical risk.