P218 Vitamin D status in IBD patients: a comparison of three different assays
A. Krajcovicova*, T. Hlavaty, Z. Leskova, J. Payer
Faculty of Medicine Comenius Univeristy and University Hospital Bratislava , 5th Department of Internal Medicine , Bratislava, Slovakia
Vitamin D (VD) is a fat soluble secosterol that is produced in the skin after the sun exposure. Epidemiological studies show significant associations of VD deficiency and immune mediated diseases. The plasma 25-OH vitamin D3 concentration is a reliable biomarker for VD status but assay's variability makes adequate monitoring of VD difficult.
The aim of this study was to determine the correlation between three different assays for measuring plasma concentration of 25(OH)-vitamin D3.
Blood samples from 50 IBD patients were evaluated in a blinded way in three different laboratories using diverse assays of 25 (OH) vitamin D monitoring such as high-performance liquid chromatography (A), IDS automated immunoassay (B) and competitive binding assay (C). We correlated the VD levels of different assays using Pearson correlation coefficient. In addition, we evaluated the clinical accuracy of each assay by examining the agreement of assays in sorting patients into distinct categories according to difference of VD levels using the cutoffs (< 5ng/ml) for acceptable agreement, (5-10ng/ml) significantly different and ( >10ng/ml) insufficient.
25(OH) vitamin D concentrations assessed by competitive binding assay were in the range of 3.0 ng/ml to 39.3 ng/ml, by high-performance liquid chromatography of 4.6 ng/ml to 53.2 ng/ml and by automated immunoassay of 9.0 ng/ml to 48.0 ng/ml. All vitamin D assays showed a linear quantitative correlation (Pearson r=0.69 for A vs. B, 0.69 for A vs. C and 0.63 for B vs.C). Comparing VD assays according to difference of VD we observed agreement in 20 samples, significant difference in 18 samples and disagreement in 10 samples between A and C; agreement in 29 samples, significant difference in 10 samples and disagreement in 9 samples between A and B; agreement in 18 samples, significant difference in 20 samples and disagreement in 12 samples between B and C.
There is a clinically important bias between different VD assays.. Our Results indicate the need towards further standardizing assays for 25(OH)D measurement.