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A simple, sensitive and reproducible assay for pyridoxal 5'-phosphate and 4-pyridoxic acid in human plasma

Bates, C.J.; Pentieva, K.D.; Matthews, N.; Macdonald, A.

Clinica Chimica Acta; International Journal of Clinical Chemistry 280(1-2): 101-111

1999


ISSN/ISBN: 0009-8981
PMID: 10090528
DOI: 10.1016/s0009-8981(98)00173-9
Accession: 010098693

We describe a procedure for the measurement of pyridoxal 5'-phosphate and of 4-pyridoxic acid in human plasma samples. It is based on the conversion of pyridoxal 5'-phosphate to 4-pyridoxic acid 5'-phosphate by cyanide in alkaline medium, followed by a high pressure liquid chromatographic separation, with fluorescence detection at acid pH. The assay is robust, sensitive, linear over a wide range, reproducible, and simple to perform. Samples stored at -80degreeC are stable. Satisfactory agreement was obtained with results from the tyrosine decarboxylase-based assay for pyridoxal 5'-phosphate, in two other laboratories. Plasma samples from a National Survey of older British people were analyzed, and reference intervals for plasma pyridoxal 5'-phosphate intervals were derived. From the lower 2.5 percentile of the reference group, taken as the lower cut-off of the normal range, ca. 20% of elderly men and 11% of elderly women in the UK showed evidence of biochemical deficiency.

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