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Editor,—There are currently two types of measurements that are used to assess vitamin B6 status. These are measurements of vitamin B6 and its metabolites, and activation of vitamin B6 dependent enzymes and associated amino acids. Tryptophan loading test is also used to reveal the subtle defects by stressing the B6 metabolic pathway. None of them is ideal, and a combination of them is recommended.
Additionally, there is no concordance between these indices. Transaminase activity in serum and red blood cells (functional index) decreases along with plasma pyridoxal phosphate, urine B6, and pyridoxic acid (direct chemical index) within one week of the removal of vitamin B6 from the diet. Electromyelographic abnormalities appear within three weeks.1 Some population groups have a suboptimal intake with or without excess protein intake, although severe vitamin B6 deficiency is not common in man.2
Epileptiform convulsions are a common finding in young vitamin B6 deficient subjects.1 These (sub)clinical deficiencies can be routinely screened by a clinical laboratory if simple tests like transaminases are used. Vitamin B6 deficiency in a well nourished child with an autosomal recessively inherited Δ1-pyrroline-5-carboxylate dehydrogenase deficiency led to childhood fits, because of binding of the proline metabolite, pyrroline-5-carboxylate with vitamin B6, as reported by Walkeret al.3 It would be interesting to know if and how the authors had measured the transaminases. Their results could indicate if this is a cost and clinically effective screening test.