Reliability of the dual-isotope Schilling test for the diagnosis of pernicious anemia or malabsorption syndrome.

To evaluate the dual-isotope Schilling test for the diagnosis of pernicious anemia or malabsorption syndrome, 65 studies were selected for clinical correlation. Criteria for pernicious anemia included mean corpuscular volume greater than 100 cu micrometer, serum B12 greater than 100 ng/l, megaloblastic marrow, achlorhydria, reticulocytes greater than 5% on B12 therapy, atrophic gastritis, and elevated serum antibodies to parietal cells or intrinsic factor. Criteria for malabsorption syndrome included: decreased serum B12, folate, and carotene; increased fecal fat; abnormal D-xylose absorption; abnormal radiographic and biopsy findings. 58Co-cyanocobalamin and 57Co-cyanocobalamin bound to intrinsic factor were given orally to fasting patients; 1 mg of nonradioactive B12 was injected intramuscularly within two hours. Aliquots of 24-hour urine samples were counted. If the excretion of 58Co was less than 7% and the 57Co/58Co ratio was greater than 1.7, the test indicated pernicious anemia; a ratio less than 1.7 indicated malabsorption syndrome. Sensitivity, specificity, and accuracy of the dual-isotope Schilling test were 83%, 98%, and 94% for pernicious anemia, and 67%, 90%, and 86% for malabsorption syndrome, respectively.