COBALAMIN ABSORPTION AND SERUM HOMOCYSTEINE AND METHYLMALONIC ACID INELDERLY SUBJECTS WITH LOW SERUM COBALAMIN

We prospectively studied 41 consecutive elderly patients with serum co balamin (vitamin B-12) levels lower than 125 pmol/l. The protein-bound cobalamin absorption test (PBAT) was performed in 34 of them and in 2 7 selected elderly control patients. The lower decision limit was 0.18 % and an abnormal test was detected in only 9 (26%) of the 34 patients with low serum cobalmin level. When the PBAT was compared to the Schi lling (Dicopac method) test, a concordant result was found in 80%. Ser um methylmalonic acid and/or total homocysteine concentrations were el evated in 75% (26/35) of the patients with low serum cobalamin levels but also in 30% (5/17) of the control patients. Of the 12 and 9 cobala min-deficient patients with elevated serum levels of methylmalonic aci d and homocysteine, normalization after cobalamin therapy was obtained in 11 and 5 respectively. In conclusion, determination of serum metab olites and their response to cobalamin therapy are a sensitive index o f significant cobalamin deficiency and a useful means of distinguishin g between cobalamin and folate deficiency. The PBAT offers little adva ntage over the Schilling test in-diagnosing cobalamin malabsorption in elderly patients.