Background: The causes of cobalamin (vitamin B12) deficiency
in older people are only partly understood. We investigated the role of the
cobalamin-binding proteins and tested the hypothesis that low saturated
transcobalamin concentration is an early marker of cobalamin deficiency.
Methods: We measured saturated (holo) and unsaturated (apo)
transcobalamin and haptocorrin concentrations in healthy middle-aged volunteers,
healthy older volunteers, cobalamin-deficient older volunteers and
cobalamin-deficient older patients.
Results: Holo and apo concentrations of transcobalamin and haptocorrin
were similar in healthy middle-aged and older subjects. Holotranscobalamin
concentrations were significantly decreased in cobalamin-deficient subjects but did
not differ between healthy volunteers and patients. Furthermore, the relative amount
of cobalamin on transcobalamin (i.e. holotranscobalamin/holotranscobalamin +
holohaptocorrin) was similar in all four groups.
Conclusions: Abnormalities of the cobalamin-binding proteins are not a
cause of cobalamin deficiency in the aged. Plasma holotranscobalamin concentration
did not differ between stages of cobalamin deficiency in older persons. Therefore,
plasma holotranscobalamin is not an early marker of cobalamin deficiency in older
people and has no additional value in the diagnostic work-up of reduced plasma
cobalamin concentrations in older people.
