[Diagnosis of vitamin B12 deficiency: only apparently child's play].

We performed a systematic literature search for diagnostic criteria in establishing cobalamin deficiency. The diagnostic procedure is particularly uncertain in elderly patients with neurological symptoms and in cases with borderline cobalamin values. In any patient with suspected cobalamin deficiency we recommend analysing a full blood count and determining cobalamin concentration in a serum sample. Particularly in elderly patients and cases with neurological symptoms presenting borderline cobalamin values and no abnormalities in the blood count, we recommend further investigation with methylmalonic acid, homocystein and Schilling test. These additional tests should make it possible to decide whether to recommend lifelong substitution with cobalamin. Various cobalamin assays, Schilling test, food cobalamin test, gastroscopic evaluation and the problems surrounding these assays in the elderly are discussed. Our own experience with methylmalonic acid, homocystein determination and food cobalamin test did not reveal a simple diagnostic procedure in such cases. We conclude that there is still no "gold standard" for diagnostic procedure in the special cases mentioned.