SCHILLING AND PROTEIN-BOUND COBALAMIN ABSORPTION TESTS ARE POOR INSTRUMENTS FOR DIAGNOSING COBALAMIN MALABSORPTION

Objectives, To assess the advantage of a protein-bound cobalamin absor ption test (PBAT) over the Schilling test in patients with suspected c obalamin (vitamin B-12) malabsorption. Design. Clinical study of conse cutive patients referred from primary care units, medical and neurolog ical clinics. Setting. The catchment area of Sahlgrenska University Ho spital, Goteborg. Subjects. Referred patients (n = 155) with suspected cobalamin deficiency and at least one serum cobalamin value < 200 pmo l L-1. Interventions. All patients were investigated with upper gastro intestinal endoscopy with biopsies taken from the gastric body and duo denal mucosa. Serum methylmalonic acid (MMA) and homocysteine (Hcy) we re determined in all 109 patients not on cobalamin substitution. A dua l isotope cobalamin absorption test was then performed with the concom itant administration of crystalline (Schilling) and protein-bound coba lamin (PBAT). Main outcome measures. Number of patients with gastric b ody atrophy diagnosed with each absorption test and the relation betwe en these results and functional cobalamin deficiency defined as elevat ed MMA and Hey, that normalized after cobalamin substitution treatment . Results. The majority of patients with abnormal absorption tests had already developed elevated MMA and/or Hcy. PBAT was more sensitive th an the Schrilling test in identifying patients with gastric body atrop hy but the sensitivity was too low for clinical use. About 1/3 of the patients with gastric body atrophy and normal absorption tests had ele vated MMA and/or Hey, indicating cobalamin deficiency. Conclusion. PBA T may be somewhat more sensitive than the Schilling test but neither t est is sensitive enough for diagnosing cobalamin malabsorption at an e arly stage.