Blood, 1958, Vol. 13, No. 6, pp. 582-588.
© 1958 American Society of Hematology, Inc.
Quantitative Assay of Intrinsic Factor Activity by Urinary
Excretion of Radioactive Vitamin B12
LEON ELLENBOGEN 1 and
WILLIAM L. WILLIAMS 1
1 Nutrition and Physiology Section, Research Division, American Cyanamid
Company, Pearl River, N. Y.
A technic for assaying consecutively up to 18 intrinsic factor preparations
with one pernicious anemia patient is described. The use of repeated flushing doses appeared to have little effect on the respsonse in the urinary excretion test; nine patients were given up to 38 flushing doses of 1 mg. of
nonradioactive B12 over a period of 44 days and showed essentially the
same response to a standard intrinsic factor preparation at the beginning
and end of this period.
The excretion of vitamin B12 in the test increased with increasing amounts
of intrinsic factor in each of four different preparations, indicating that
large amounts of intrinsic factor did not inhibit absorption. There was no
relationship between the urinary excretion values obtained with radioactive
B12 alone and the values obtained with radioactive B12 plus standard intrinsic
factor in a series of tests on 127 pernicious anemia patients. It appears that
total rather than net excretion values are to be preferred in evaluating preparations. Since it has been shown that pernicious anemia patients given intrinsic factor absorb more than 0.5 µg. of radioactive vitamin B12, an oral
dose of 2.0 µg. of B12 which allows an absorption of more than 0.5 µg. is
preferred in order to extend the range of intrinsic factor test doses that can
be assayed.
Submitted on August 26, 1957
Accepted on January 18, 1958
