Cobalamin Deficiency in General Practice. Assessment of the Diagnostic Utility and Cost- Benefit Analysis of Methylmalonic Acid Determination in Relation to Current Diagnostic Strategies

Diagnosing cobalamin deficiency is often difficult. We investigated the diagnostic strategies that 224 general practitioners used to assess cobalamin status and the criteria on which they based their decisions to supple-ment patients. From all serum cobalamin analyses car-ried out at a single laboratory during 1993, individuals with serum cobalamin concentrations <300 pmol/L were identified, and one patient per general practitioner was included. When serum methylmalonic acid (s-MMA) values>0.376 mmol/L were used as the “reference stan-dard ” for cobalamin deficiency, the serum cobalamin assay had a diagnostic sensitivity of 0.40 and a specific-ity of 0.98. With the same reference standard, the diag-nostic accuracy of the physicians ’ decision to supple-ment patients had the same specificity but a highe