No biological marker, whether old school (fractional excretion of sodium or urea, urinary sodium (UNa,) urine-to-plasma creatinine ratio (U:PCr), etc) or new biomarkers such as Cystatin C, urinary neutrophil gelatinase-associated lipocalin (N-GAL), has clearly demonstrated a capacity to correctly classify AKI [6, 14, 20, 21]. The gene discussed is CST3; the disease is acute kidney injury.