Abstract: FR-PO277

The Impact of CKD on Analytical Performance of 25 Vitamin D Assays

Session Information

Category: Mineral Disease

  • 1202 Mineral Disease: Vitamin D, PTH, FGF-23


  • Guapyass? Machado, Hanna Karla A., Universidade de São Paulo, São Paulo, Brazil
  • Martins, Carolina Steller wagner, Universidade de São Paulo, São Paulo, Brazil
  • Jorgetti, Vanda, Universidade de São Paulo, São Paulo, Brazil
  • Elias, Rosilene M., Universidade de São Paulo, São Paulo, Brazil
  • Moyses, Rosa M.A., Universidade de São Paulo, São Paulo, Brazil

Current guidelines recommend evaluation of 25 vitamin D (25vitD) status and therapy when serum levels are below 30 ng/ml. Significant differences among some assays have been described. However, the impact of renal disease on these differences has never been assessed yet. In our service, the assay for 25vitD measurement was changed from Diasorin® to Beckman Coulter Unicel DXI 800®, which gave us the opportunity to evaluate the impact of the assay in the levels of 25vitD in CKD patients.


We obtained data from 540 patients [122 with eGFR > 90 ml/min (normal renal function); 138 with 30-60 ml/min (CKD3); 124 with 15-29 ml/min (CKD4) and 156 on dialysis (CKD5D)] in which serum 25vitD was measured with both assays with a time difference of 6 months.


The median of serum 25vitD increased [23 (19-29) vs. 29 (22-37) ng/ml; p=0.0001], but could not be explained by seasonal differences, as the second measurement was done at wintertime. 25vitD increased in patients with CKD 3, 4 and 5D, but not in individuals with normal renal function. Indeed, the more advanced the CKD, the higher the median increase [-5 ng/ml (-9.3-4) in normal renal function; 3.5 ng/ml (-2.8-11) in CKD3; 3 ng/ml (-1.3-9) CKD4; and 8 ng/ml (1-15) in CKD5D; p<0.0001). The prevalence of 25vitD insufficiency increased from 49 to 62% in the entire population and from 44 to 57% only in CKD patients (p = 0.001 and 0.0001, respectively).


Our findings confirm the disagreement between 25vitD assays, showing higher levels with Beckman Coulter Unicel DXI 800®, which is more marked in CKD patients, suggesting that non-active fragments usually found in this population might be recognized as intact 25vitD. This technical problem will certainly affect hypovitaminosis D diagnosis and also therapy in CKD patients.


  • Government Support - Non-U.S.