Studies were made in pernicious anemia patients on the urinary excretion of B12Co60 after a small oral dose followed by a large parenteral injection of nonradioactive vitamin B12.
(1) Increasing doses of intrinsic factor concentrates give increasing excretions of radioactivity at low doses; little additional increase at moderate doses; and at times a subsequent diminution at excessive doses. Data on 34 tests of a particular intrinsic factor concentrate in 18 pernicious anemia patients tend to support an excretion proportional to the logarithm of intrinsic factor dosage at low to moderate levels, but do not exclude the possibility of a linear approach to a plateau.
(2) Assay by hematologic response was compared with the urinary excretion tests in 13 pernicious anemia patients. This data shows a relation between the two tests though the correlation is far from complete.
(3) Methods are outlined for testing all intrinsic factor preparations with the same amount of tracer vitamin B12 as will be incorporated commercially. More sensitive comparative tests of similar intrinsic factor preparations may be made using smaller amounts of B12Co60.
(4) The literature is reviewed to determine which variations in technic might lead to the most reliable quantitation of intrinsic factor activity.