[Cobalamin deficiency despite normal serum cobalamins].
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.
Rasmussen
K
K
Arhus Kommunehospital, klinisk-kemisk afdeling.
Pedersen
K O
KO
Sillesen
S
S
D000368:Aged; D002624:Chemistry, Clinical / Q000379:methods; D006801:Humans; D008297:Male; D008764:Methylmalonic Acid / Q000097:blood*; D014805:Vitamin B 12 / Q000097:blood; D014806:Vitamin B 12 Deficiency / Q000097:blood*
D008764:Methylmalonic Acid; D014805:Vitamin B 12
Cobalaminmangel trods normale serum-cobalaminer.