Urine apoptosis inhibitor of macrophage is an early predictor of acute kidney injury post- cardiac surgery

Abstract Background: Acute kidney injury (AKI) has high morbidity and mortality. Apoptosis inhibitor of macrophage (AIM) is key to improving AKI, enhancing the phagocytic clearance of dead cells within proximal renal tubules. Free AIM (fAIM) comprises short fAIM (S-fAIM) and full-length fAIM (F-fAIM). Although S-fAIM and F-fAIM appear in the urine during AKI, the association between AKI prognosis and AIM remains unclear. Methods: We studied 102 patients who underwent cardiac surgery from December 2020 to June 2021. Urine was sampled before and after surgery. fAIM and F-fAIM were analysed using a bioluminescent enzyme immunoassay. Other markers of AKI were also measured. Results: Thirty-seven patients developed AKI post-surgery, diagnosed according to the KDIGO guidelines. Mean fAIM and F-fAIM concentrations were significantly higher in patients with AKI than in patients without AKI 0 h post-surgery ( p < 0.001 and p = 0.003, respectively) but decreased rapidly 3 h later. Urinary fAIM and F-fAIM had an area under the curve values of 0.72 and 0.67, respectively, 0 h post-surgery. fAIM and F-fAIM levels showed similar kinetics to those of neutrophil gelatinase-associated lipocalin and liver-type fatty acid-binding protein. Conclusions: Urinary fAIM and F-fAIM excretion may be useful early biomarkers for predicting AKI in adults following cardiac surgery. fAIM and F-fAIM may be comparable in their diagnostic ability with the currently known markers of AKI.