The measurement of serum pyridoxal by a microbiological assay using Lactobacillus casei

A new method has been developed for the assay of serum pyridoxal using L. casei. Bound pyridoxal phosphate in serum is converted by acid hydrolysis to pyridoxal for which this organism is specific. This method proved to be considerably more sensitive than other methods so far reported in the literature. Serum pyridoxal concentrations were measured in 151 control subjects aged 17 to 80 years. The range of concentrations found was 1.5 to 13.5 ng/ml which compared well with values obtained by most workers measuring pyridoxal phosphate by enzymatic methods. A marked fall with age was confirmed, and levels in women of childbearing age were lower than in men of comparable age. Subnormal serum pyridoxal concentrations were found in 62% of patients with sideroblastic anaemia and in the majority of patients with rheumatoid arthritis, Crohn's disease, coeliac disease, and in pregnant women at term.