A simple, sensitive and reproducible assay for pyridoxal 5'-phosphate and 4-pyridoxic acid in human plasma.
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 -80 degrees C 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.
Bates
C J
CJ
MRC Human Nutrition Research, Cambridge, UK. chris.bates@mrc-hnr.cam.ac.uk
Pentieva
K D
KD
Matthews
N
N
Macdonald
A
A
D000368:Aged; D002851:Chromatography, High Pressure Liquid; D005260:Female; D006801:Humans; D008297:Male; D011732:Pyridoxal Phosphate / Q000097:blood*; D011735:Pyridoxic Acid / Q000097:blood*; D012016:Reference Values; D015203:Reproducibility of Results; D012680:Sensitivity and Specificity; D013050:Spectrometry, Fluorescence
D011735:Pyridoxic Acid; D011732:Pyridoxal Phosphate