Diabetic nephropathy(DN)is a major microvascular complication of diabetes.Renal injury may be presented with the characteristics of albuminuria, and its main pathological change is glomerular sclerosis. However, both glomerular lesions such as glomerulosclerosis, glomerular basement membrane thickness and tubulointerstitial fibrosis have been found in both type 1 and type 2 diabetic patients with normal urinary albumin excretion rate, moreover the tubular injury may be the primary pathological change in diabetic renal injury not only the secondary change brought on by glomerular injury. Thus, if overt urinary albumin exists in T2DM patients, the tubular injury may be severe already. An index which is predominant, sensitive and convenient to be measured should be purposed.It is predicted that insufficient renal 1-alpha hydroxylase may play a critical role in diabetic nephropathy. Then the investigators present the presumption that the activity of renal 1-alpha hydroxylase could reflect the degrees of tubulointerstitial injury, using serum 1,25-dihydroxyvitamin D level as an index.

Inclusion Criteria:

• age >18 years, DM duration >1 year, all of the patients were predialysis

Exclusion Criteria:

• history of liver or kidney disease, malignancy, current pregnancy, extensive dermatologic disease, evidence of metabolic bone disease and hyper-/hypo- thyroidism that would affect mineral metabolism. Patients who were taking native or active vitamin D, steroids, phosphate binders, or medications that affect vitamin D metabolism were also excluded.

Patients with T2DM were recruited from the general hospital of Tianjin Medical University in China .