N05076: The analysis of 25-hydroxy vitamin D to compare four different methods
Wednesday 9 July 2008
Background
Background:
This project compared four different analytical methods used to measure 25-hydroxy vitamin D concentrations (25OHD) in blood plasma. The aim was to find the most appropriate method for use in FSA projects N05062, 63 & 64. The four methods compared were:
- A radio-immuno assay (RIA) (by Diasorin)
- An enzyme-linked immuno assay (EIA) (by Immunodiagnostic Systems)
- Liquid-Chromatography with Mass spectrometry (LC/MS)
- High pressure liquid chromatography (HPLC)
Research Approach
Pooled plasma samples from the National Diet and Nutrition Survey population (n=20) were prepared and aliquots of these samples were sent to each of the four participating laboratories. In addition each laboratory also received four quality control samples. Each laboratory employed one of the four methods. The obtained results were statistically analysed using the Bland Altman procedure.
Results and findings
This project found reasonable agreement between the RIA, EIA and HPLC methods. The 25OHD concentrations for the EIA were found to be around 4.6 nmol/L higher than those obtained by RIA. HPLC was found to give results around 3.7nmol/L lower than those obtained by RIA and around 8nmol/L lower than the EIA results. The agreement between LC/MS and the other three methods was relatively weak.
On the basis of this project’s result and taking into account practical considerations it was decided that the enzyme-linked immuno assay (EIA) would be the method most appropriate for use in projects N05062, 63 & 64.