RALPH CARMEL, M.D.
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To the editor: In the October 1979 issue Drs. Jacobson and Onstad (1) described a Schilling test artifact caused by inactive commercial intrinsic factor. That report is an important reminder of the vagaries of commercial preparations and illustrates why each laboratory should monitor its methods and materials and not abandon this function to the suppliers. Similar intrinsic factor potency problems in a different laboratory procedure have also contributed to artifactual results in the radioassay for serum vitamin B12 (2).
Still another intrinsic factor problem in testing vitamin B12 absorption can be mentioned. Confusing results may occur with the so-called "double-isotope"
CARMEL R. The Schilling Test. Ann Intern Med. ;92:570–571. doi: 10.7326/0003-4819-92-4-570_2
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Published: Ann Intern Med. 1980;92(4):570-571.
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