[Applying Serum Vitamin D Metabolites in the Assessment of Renal Impairment in Diabetic Kidney Disease of Type 2 Diabetes Mellitus Patients: A Retrospective Study].

Objective: Total 25(OH)D (t-25[OH]D), a marker traditionally used in the assessment of vitamin D (VitD) in the human body, includes 25(OH)D , 25(OH)D , and C -epimers-25(OH)D (C -epi). In this study, we analyzed the relationship between serum VitD metabolites and renal impairment in patients with diabetic kidney disease (DKD).

Methods: We covered, in the study, 339 subjects, including 114 otherwise healthy controls (HC), 74 type 2 diabetes mellitus (DM) patients with no glomerular filtration dysfunction, and 151 DKD patients. According to the results of combined evaluation of estimated glomerular filtration rate (eGFR) and urine albumin-to-creatinine ratio (UACR), the DKD patients were further divided into four subgroups, stage 2 subgroup of patients of DM combined with stage-2 chronic kidney disease (CKD2), stage 3 subgroup of patients of DM combined with CKD3, stage 4 subgroup of patients of DM combined with CKD4, and stage 5 subgroup of patients of DM combined with CKD5. The levels of 25(OH)D , 25(OH)D , and C -epi were measured by ultra performance liquid chromatography-tandem mass spectrometry (UPLC-MS/MS), and the activity level of 25(OH) (AVitD ), t-25(OH)D concentration, 25(OH)D /25(OH)D ratio, C -epi/t-25(OH)D ratio, and C -epi/AVitD ratio were calculated.

Results: The levels of 25(OH)D , t-25(OH)D, and AVitD were lower in the DKD group than those in the DM and HC groups (all <0.05). C -epi/t-25(OH)D ratio and C -epi/AVitD ratio were higher in the DKD group than those in the HC group (all <0.05). The levels of 25(OH)D , t-25(OH)D, AVitD , and C -epi were lower in the stage 5 subgroup than those in the stage 2 and stage 3 subgroups (all <0.05). The levels of 25(OH)D , t-25(OH)D, and C -epi were lower in the stage 4 subgroup than those in the stage 3 subgroup (all <0.05). The 25(OH)D , t-25(OH)D, and AVitD levels were lower in the stage 4 subgroup than those in the stage 2 subgroup (all <0.05).

Conclusions: UPLC-MS/MS can be used to perform accurate evaluation of VitD nutritional status in DKD patients. DKD patients have decreased levels of serum t-25(OH)D, 25(OH)D , and AVitD , all of which progressively decrease along with the rise in CKD staging. The trend of C -epi and 25(OH)D changes were not consistent.