METHYLMALONIC ACID AND HOMOCYSTEINE IN PLASMA AS INDICATORS OF FUNCTIONAL COBALAMIN DEFICIENCY IN INFANTS ON MACROBIOTIC DIETS

Methylmalonic acid and total homocysteine in plasma and serum have pre viously been used as indicators of intracellular cobalamin function in adults. To assess the usefulness of quantitation of these metabolites in the diagnosis of dietary cobalamin deficiency in infants, they wer e determined in plasma from 41 infants (aged 10-20 mo) on a macrobioti c diet and in 50 healthy group-matched omnivorous controls. In the mac robiotic infants, both methyhlmalonic acid and total homecysteine were markedly increased compared with controls (8-fold and 2-fold, respect ively). Both metabolites showed an inverse relation to the plasma coba lamin level. The very low cobalamin content of the macrobiotic diet an d low plasma cobalamin in macrobiotic infants makes an impaired cobala min function likely in these infants. We therefore used dietary group as an independent indicator of cobalamin status. Different test parame ters for cobalamin status were evaluated by comparing their ability to discriminate between the two dietary groups. Logistic regression anal ysis showed that methylmalonic acid followed by total homecysteine and cobalamin, in that order, were the strongest predictors of dietary gr oup. Mean corpuscular volume and Hb had low discriminative power. We c onclude that the determination of methylmalonic acid and total homocys teine represents a sensitive and specific test for the diagnosis and f ollow-up of nutritional cobalamin deficiency in infants. Furthermore, the finding of high methylmalonic acid and total homocysteine in plasm a of most macrobiotic infants demonstrates a functional cobalamin defi ciency in these subjects.