title: Effects of methodological variation on assessment of riboflavin status using the erythrocyte glutathione reductase activation coefficient assay.
abstract: Riboflavin status is usually measured as the in vitro stimulation with flavin adenine dinucleotide of the erythrocyte enzyme glutathione reductase, and expressed as an erythrocyte glutathione reductase activation coefficient (EGRAC). This method is used for the National Diet and Nutrition Surveys (NDNS) of the UK. In the period between the 1990 and 2003 surveys of UK adults, the estimated prevalence of riboflavin deficiency, expressed as an EGRAC value > or = 1.30, increased from 2 to 46 % in males and from 1 to 34 % in females. We hypothesised that subtle but important differences in the detail of the methodology between the two NDNS accounted for this difference. We carried out an evaluation of the performance of the methods used in the two NDNS and compared against an 'in-house' method, using blood samples collected from a riboflavin intervention study. Results indicated that the method used for the 1990 NDNS gave a significantly lower mean EGRAC value than both the 2003 NDNS method and the 'in-house' method (P < 0.0001). The key differences between the methods relate to the concentration of FAD used in the assay and the duration of the period of incubation of FAD with enzyme. The details of the EGRAC method should be standardised for use in different laboratories and over time. Additionally, it is proposed that consideration be given to re-evaluating the basis of the EGRAC threshold for riboflavin deficiency.
authors.affiliation: Human Nutrition Unit, School of Medicine and Biomedical Sciences, University of Sheffield, Sheffield S102RX, UK.
authors.forename: Marilyn H E
authors.initials: MH
authors.lastname: Hill
authors.forename: Angela
authors.initials: A
authors.lastname: Bradley
authors.forename: Sohail
authors.initials: S
authors.lastname: Mushtaq
authors.forename: Elizabeth A
authors.initials: EA
authors.lastname: Williams
authors.forename: Hilary J
authors.initials: HJ
authors.lastname: Powers
mesh_terms: D000328:Adult; D004796:Clinical Enzyme Tests / Q000379:methods / Q000592:standards*; D004032:Diet; D004789:Enzyme Activation; D004912:Erythrocytes / Q000201:enzymology*; D005260:Female; D005980:Glutathione Reductase / Q000378:metabolism*; D006801:Humans; D008297:Male; D008875:Middle Aged; D009749:Nutrition Surveys; D009752:Nutritional Status; D012016:Reference Values; D012256:Riboflavin / Q000097:blood*; D012257:Riboflavin Deficiency / Q000175:diagnosis*; D012680:Sensitivity and Specificity; D018709:Statistics, Nonparametric; D006113:United Kingdom; D055815:Young Adult
chemical_list: D005980:Glutathione Reductase; D012256:Riboflavin