METABOLIC COBALAMIN DEFICIENCY IN PATIENTS WITH LOW TO LOW-NORMAL PLASMA COBALAMINS

Over a 2-year period, we examined 48 patients with P-cobalamin levels in the difficult ''grey zone'' at the lower reference limit detected b y a competitive protein binding assay using intrinsic factor as binder . In 21 of 30 patients (70%) with low P-cobalamins we could not establ ish the diagnosis of metabolic cobalamin deficiency, but 1 of 18 patie nts (6%) with low-normal P-cobalamin values was confirmed metabolicall y cobalamin-deficient. Half of these 30 patients with low P-cobalamins had neuropsychiatric disorders, but only one-third of the latter pati ents had metabolic cobalamin deficiency. Ten of the remaining 15 patie nts (67%) were characterized as non-deficient. In patients with low-no rmal P-cobalamin level, we found neuropsychiatric disorders in 5 of th e 18 (28%), but none of these had metabolic cobalamin deficiency. We c onclude that P-cobalamins below the reference interval combined with t ypical neuropsychiatric symptoms or findings are not diagnostic of cob alamin deficiency and that further analyses are necessary.