Cut-off value and diagnostic strengths of serum cystatin C at T0 Diagnotic parameters Cut-off Youden index Se (%) Sp (%) PPV (%) NPV (%) Cystatin C (mg / L) 0.765 0.404 80.35 61.29 71.4 69.0 - At the cut-off of 0.76mg / L, the sensitivity and specificity of serum cystatin C in diagnosing AKI were 80.35% and 61.29% respectively.