Physicians' use of plasma methylmalonic acid as a diagnostic tool.

Objectives. To investigate physicians' reasons for requesting plasma methylmalonic acid and their reactions to an increased concentration of plasma methylmalonic acid. Design. Study of medical records. Setting. Three somatic district hospitals in Denmark. Subjects. Medical records of 198 patients with a plasma methylmalonic acid measurement above the reference interval. Information on diagnostic decisions was available for 177 patients. Main outcome measures. Reasons for requesting plasma methylmalonic acid and the reactions to the finding of elevated plasma methylmalonic acid. Results. An explicit reason for requesting plasma methylmalonic acid was stated in 57% of 198 examined medical records, known or suspected anaemia being the most frequent reason. No further action was taken in 109 (62%) of the 177 cases available for follow-up. Amongst the remaining 68 patients, the finding of an increased plasma methylmalonic acid led to diagnosis of cobalamin deficiency in 46 patients. Six patients with a markedly increased plasma methylmalonic acid (above 0.99 μmol L -1 ) and clearly decreased plasma cobalamins (below 200 pmol L -1 ) were not recognized as having cobalamin deficiency. Conclusions. This lack of response to an increased plasma methylmalonic acid raises an important question. Is the clinical response inadequate, or is the connection between an increased level of plasma methylmalonic acid and signs of clinical significant cobalamin deficiency less clear?