High performance liquid chromatography method for the determination of pyridoxal-5-phosphate in human plasma: how appropriate are cut-off values for vitamin B6 deficiency?
OBJECTIVE
Application of a HPLC (high performance liquid chromatography) method, using cyanide derivatisation, to the determination of plasma pyridoxal-5-phosphate (PLP) concentrations as an indicator of vitamin B6 adequacy.


METHODS
The study was performed at the Institute of Food Research, Norwich, UK. Blood samples were taken at the Institute, at Health Centres, or in the volunteer's home.


METHODS
51 adolescent, 131 adult, 68 non-institutionalized elderly and 44 aged (>73 y) volunteers were recruited from local authority schools, local Health Centres and General Practitioners.


RESULTS
The mean PLP recovery was 92.8%. The intra- and inter-assay coefficients of variation were 2.8% and 5.2% respectively. Mean PLP concentrations for males and females, respectively, were: adolescents (13-14 y), 36.4 and 43.5 nM; adults (20-64 y), 39.2 and 40.0 nM; elderly (68-73 y), 34.8 and 35.3 nM; aged (>73 y), 57.8 and 49.0 nM. Percentages of subjects with PLP concentrations <34.4 nM were over 26% in all population groups. Mean vitamin B6 intakes (microg/g protein intake), as assessed by weighed dietary records, were all above reference nutrient intakes (15 microg/g protein).


CONCLUSIONS
An HPLC method, using cyanide derivitisation, has been applied to the determination of plasma PLP. Comparisons of results for local population groups with current cut-off values for plasma PLP, show large numbers of volunteers at risk of vitamin B6 deficiency although this is not reflected by vitamin B6 intakes calculated from food tables. The 34.4 nM cut-off value for value for plasma PLP, indicating deficiency, is questioned.
Nutrition, Diet and Health Department, Institute of Food Research, Norwich Research Park, UK.
A L
AL
Bailey
A J
AJ
Wright
S
S
Southon
D000293:Adolescent; D000328:Adult; D000368:Aged; D000704:Analysis of Variance; D002851:Chromatography, High Pressure Liquid / Q000379:methods*; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D011732:Pyridoxal Phosphate / Q000097:blood*; D011736:Pyridoxine / Q000008:administration & dosage; D012016:Reference Values; D026681:Vitamin B 6 Deficiency / Q000097:blood* / Q000175:diagnosis
D011732:Pyridoxal Phosphate; D011736:Pyridoxine