Biomarkers are biological parameters that can be objectively measured and evaluated, which act as indicators of normal or pathological processes, or of the response to intervention. The sensitivity, specificity and time course of a biomarker are critical factors in determining the utility of a particular biomarker in a disease process. A surrogate outcome biomarker is one which faithfully tracts a disease including early prediction of renal function impairment, the response to therapy, and renal function recovery.