Vitamin D insufficiency and deficiency is common in chronic kidney disease (CKD) patients and is associated with elevated parathyroid hormone (PTH) concentration and mineral and bone disorder (MBD). There is also increasing evidence to show that these abnormalities increase cardiovascular morbidity and mortality in CKD patients. There is a need for early identification of vitamin D insufficiency/deficiency in CKD patients to prevent its long-term complications. However, the vitamin D status of CKD patients in Singapore has not been well described. The purpose of this study is to assess the vitamin D status of predialysis CKD patients in a tertiary academic teaching hospital in Singapore, and its association with parameters for MBD. Predialysis patients from the outpatient renal clinic at the National University Hospital (NUH) will be recruited into this study. Blood samples from the patients will be collected after an overnight fast to determine their serum 25(OH)D, creatinine, phosphorus, calcium, albumin and i-PTH concentrations. These parameters will be compared among patients in various stages of CKD.