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-25OHD), a marker traditionally used in the assessment of vitamin D (VitD) in the human body, includes 25(OH)D₂, 25(OH)D₃, and C₃-epimers-25(OH)D₃ (C₃-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)D₂, 25(OH)D₃, and C₃-epi were measured by ultra performance liquid chromatography-tandem mass spectrometry (UPLC-MS/MS), and the activity level of 25(OH)₃ (AVitD₃), t-25(OH)D concentration, 25(OH)D₂/25(OH)D₃ ratio, C₃-epi/t-25(OH)D ratio, and C₃-epi/AVitD₃ ratio were calculated.

  Results  The levels of 25(OH)D₃, t-25(OH)D, and AVitD₃ were lower in the DKD group than those in the DM and HC groups (all P<0.05). C₃-epi/t-25(OH)D ratio and C₃-epi/AVitD₃ ratio were higher in the DKD group than those in the HC group (all P<0.05). The levels of 25(OH)D₃, t-25(OH)D, AVitD₃, and C₃-epi were lower in the stage 5 subgroup than those in the stage 2 and stage 3 subgroups (all P<0.05). The levels of 25(OH)D₃, t-25(OH)D, and C₃-epi were lower in the stage 4 subgroup than those in the stage 3 subgroup (all P<0.05). The 25(OH)D₃, t-25(OH)D, and AVitD₃ levels were lower in the stage 4 subgroup than those in the stage 2 subgroup (all P<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)D₃, and AVitD₃, all of which progressively decrease along with the rise in CKD staging. The trend of C₃-epi and 25(OH)D₃ changes were not consistent.