CST4 and acute kidney injury: In another study protocol of 76 adult patients undergoing complex valvular heart surgery by Choi et al. (2011), no significant differences in the incidence of postoperative acute kidney injury and the concentrations of serum creatinine, cystatin, or NGAL were noticed between controls and patients preconditioned with three cycles of 10-min lower limb ischemia followed by 10-min reperfusion.