The Schilling Test

The diagnosis of states of vitamin B₁₂ malabsorption, especially in patients with pernicious anemia, was enormously simplified by Schilling in 1953.¹ It had previously been noted by Conley et al² that raising the parenterally given dose of cyanocobalamin led to an increasing percent of that dose appearing in the urine. Subsequently, Schilling showed that a large injection (1 mg) of nonradioactive cyanocobalamin given two hours after oral administration of the radioisotope enhanced the percent of radioactive cyanocobalamin excreted. The mechanism involved appeared to be the blocking of vitamin B₁₂-binding sites in liver and plasma by the parenterally given drug. Thus urine could replace stool³ as biological material for measuring, albeit indirectly, vitamin B₁₂ absorption. Today, less commonly employed techniques include external hepatic scanning' and whole body counting.⁵

The patient with pernicious anemia lacks the ability to produce intrinsic factor, a thermolabile glycoprotein