FLAIR INTERCOMPARISONS ON SERUM AND RED-CELL FOLATE

Interlaboratory variation in the results for serum and red cell folate was assessed as part of the EC FLAIR Concerted Action No 10 with 11 p articipating laboratories from 7 European countries. In the first inte rcomparison freeze dried quality control serum samples at two differen t Levels were analysed using different assay methodologies (microbiolo gical, radioassay, HPLC and chemilumiscence). Considerable variability was observed both between different methods (''over-all'' coefficient of variation (CV) 18-41%), as well as between laboratories using a si milar assay kit/protocol. In the second intercomparison recovery studi es were performed with sera spiked with calibrated standard preparatio ns of pteroylmonoglutamic acid (PGA) or 5-methyltetrahydrofolic acid ( 5-MTHF). With radioassays average PGA recoveries ranged between 86-140 % (mean 110%), for 5-MTHF between 99-144% (mean: 130%). In the third i ntercomparison with commercial whole blood control samples variabiliti es (CV's) between 36 and 63% were found. These results indicate that e specially radioassays tend to overestimate serum folate content due to improper standard calibration. Also small differences in assay pH as well as matrix effects may contribute to the variability These data st ress the importance of improved standardization of (commercial) diagno stic kits and the provision of suitable reference materials with assig ned folate levels spanning its physiological concentration range.