A Micromethod for Determination of Plasma Pyridoxal Phosphate and Its Use in Assessment of Storage Stability of the Vitamer

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Abstract
A widely used macromethod employing tryrosine apodecarboxylase for measurement of pyridoxal phosphate (PLP) concentration in 0.5-1.0-ml plasma was modified to a microscale utilizing 0.1-ml plasma. Mean PLP levels in 12 plasma samples were 160.6 .+-. 32.8 pmol/ml (mean .+-. SD) when analyzed by the macromethod, and were not significantly different compared to those obtained by the micromethod (158.4 .+-. 28.2 pmol/ml). Results of the two methods were significantly correlated (r = + 0.94, p < 0.001). Plasma PLP concentrations of 11 samples determined by the micromethod (.hivin.x = 151.8 .+-. 30.0 pmol/ml) were similar and significantly correlated (r = +0.95, p < 0.001) to levels measured in the same samples 1-2 years earlier (.hivin.x = 145.1 .+-. 26.2 pmol/ml). This suggests that plasma PLP content of the samples was stable for up to 2 years of storage when the micromethod was utilized for analysis. The strong significant correlation between macro-and micromethods attests that the micromethod is a reliable alternative to the macromethod. The micromethod is useful in instances where only small samples of plasma are available for measurement of PLP.