The Total Serum Homocysteine as an Indicator of Vitamin B12 and Folate Status

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Abstract
Presented is a modification of an assay for total serum homocysteine (Hey) in which the Hey plus radioactive adenosine is converted enzymatically to labeled S-adenosylhomocysteine (AdoHcy). The modifications included a commercial source for the AdoHcy hydrolase, adenosine labeled with either 14C or 3H, and separation of the AdoHcy by thin layer chromatography. The assay was sensitive to 25 pmol. Hey levels in sera from 18 controls ranged from 6.9 to 12.1 μmol/L with a mean of 9.1 and a SD of 1.5 μmol/L. The total serum Hey was increased in vitamin B12 and folate deficiency. The level was high in congenital defects of vitamin B12 metabolism, blocking the methylation of Hey regardless of the serum vitamin B12 levels, but was normal in the absence of tissue deficiency even if the serum vitamin B12 levels were low. The procedure has been found practical in two years of use and requires only 0.1 mL of serum.