Regional Medical Laboratory

In the past the Schilling test has represented an effective way of demonstrating the impaired oral absorption of vitamin B12 seen with pernicious anemia and likewise a valuable test in assessing the significance of low serum B12 levels. Serum vitamin B12 levels may, however, be low or indeterminate in the absence of functional efficiency. More recently, measurement of serum methylmalonic acid, which is elevated in functional vitamin B12 deficiency, has been advocated as the next step in evaluating low or indeterminate vitamin B12 levels or evaluating individuals with normal vitamin B12 levels in whom functional deficiency is suspected

Once true functional deficiency of vitamin B12 has been established by documenting increased methylmalonic acid levels, malabsorption of vitamin B12 may be presumed. Without a history of prior GI disease or surgery the usual etiology is impaired absorption due to the presence of anti-parietal cell antibodies or blocking antibodies to intrinsic factor.