The finding that serum Cf48 peptide levels correlated with the area of Acta2+ myofibroblast staining in renal biopsies, and that serum Cf48 levels were significantly increased while serum levels of creatinine reduced to a normal range in a mouse model of resolving AKI accompanying renal fibrosis, indicates that serum Cf48 could be a biomarker of active renal fibrosis, and potentially predictive of disease progression. The gene discussed is ACTA2; the disease is renal fibrosis.