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  • Title: [Cobalamin deficiency despite normal serum cobalamins].
    Author: Rasmussen K, Pedersen KO, Sillesen S.
    Journal: Ugeskr Laeger; 1992 Feb 03; 154(6):346-7. PubMed ID: 1539366.
    Abstract:
    In a man aged 77 years with normal concentrations of cobalamins in the serum, the concentration of methylmalonic acid in the serum was raised (2,920 nmol/l; 50-370 nmol/l). (The serum cobalamin concentrations were measured both by an old R-binder method (400 pmol/l; reference interval 200-800 pmol/l) and by a more recent S-binder method (164 pmol/l; 95-585 pmol/l)). Following a saturation dose of vitamin B12, the serum concentration of methylmalonic acid became normal (215 nmol/l) indicating that the patient had had functional cobalamin deficiency. The clinician should never let himself be deceived by a normal concentration of cobalamins in the serum and thus discard a suspicion of cobalamin deficiency. Measurement of serum methyl-malonic acid, which is a sensitive and specific analysis to differentiate between the presence or absence of cobalamin deficiency, is recommended to elucidate cases of doubt.
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