Mild Stage 1 post-operative acute kidney injury: association with chronic kidney disease and long-term survival

BACKGROUND: Mild cases of acute kidney injury (AKI) are identified by a small rise in serum creatinine (SCr) according to the KDIGO AKI definition. The aim of this study was to examine the long-term outcomes of individuals with mild AKI. Methods. This was a retrospective cohort study of all adult patients who underwent abdominal, cardiothoracic, vascular or orthopaedic surgery at Landspitali–The National University Hospital of Iceland in 1998–2015. Incident chronic kidney disease (CKD), progression of pre-existing CKD and long-term survival were compared between patients with mild Stage 1 AKI (defined as a rise in SCr of ≥26.5 μmol/L within 48 h post-operatively without reaching 1.5× baseline SCr within 7 days), and a propensity score-matched control group without AKI stratified by the presence of CKD. RESULTS: Pre- and post-operative SCr values were available for 47 333 (42%) surgeries. Of those, 1161 (2.4%) had mild Stage 1 AKI and 2355 (5%) more severe forms of AKI. Mild Stage 1 AKI was associated with both incident CKD and progression of pre-existing CKD (P < 0.001). After exclusion of post-operative deaths within 30 days, mild Stage 1 AKI was not associated with worse 1-year survival in patients with preserved kidney function (94% versus 94%, P = 0.660), and same was true for patients with pre-operative CKD (83% versus 82%, P = 0.870) compared with their matched individuals. Conclusions. Mild Stage 1 AKI is associated with development and progression of CKD, but not with inferior 1-year survival. These findings support the inclusion of a small absolute increase in SCr in the definition of AKI.