Chronic kidney disease (CKD) is a highly-prevalent, global health problem; for example, in Japan, it is estimated that about 10 percent of the population have CKD. The number of patients with worsening kidney functions, eventually requiring costly kidney replacement therapy or transplantation, is increasing. In addition, the risk of life-threatening cardiovascular diseases increases with the progression of CKD stages. Preventing CKD patients from progressing to end-stage kidney disease is therefore critical, but unfortunately there are no effective methods to predict the progression of CKD. Currently, prediction relies on kidney functions estimated from serum creatinine and some additional information, such as proteinuria, but these are insufficient. Naturally, nephrologists are earnestly searching for better biomarkers.