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Simultaneous Measurement of Free and Intrinsic Factor (IF) Bound Vitamin B₁₂ (B₁₂) Absorption: Absolute Quantitation with Incomplete Stool Collection and Rapid Relative Measurement Using Plasma B₁₂ (IF): B₁₂ Absorption Ratio

University of California School of Medicine and San Francisco General Hospital, San Francisco, California

Correspondence: For reprints contact: Mathews B. Fish, Associate Director, Clinical Laboratories, Building 100, Room 163, San Francisco General Hospital, 1001 Potrero and 22nd Sts., San Francisco, Calif. 94110.

ABSTRACT

This report describes a procedure that involves the absolute and simultaneous measure meat of free ⁵⁸Co-labeled B₁₂ (⁵⁸Co-B₁₂) and IF-bound ⁵⁷Co-B₁₂ [⁵⁷Co-B₁₂(IF)] using a non-absorbable marker (⁶⁰Co microspheres) and incomplete stool collections. Absorption by this procedure in controls and megaloblastic folate deficient patients averaged 55% for B₁₂ and 66% for B₁₂(IF) whereas absorption in megaloblastic patients with pernicious anemia averaged 7% of B₁₂ and 34% of B₁₂(IF). These stool absorption data compared closely with simultaneous whole-body counter measurements. In addition, measurement and evaluation were made of a ⁵⁸Co-B₁₂(IF):⁵⁷Co-B₁₂ ratio in a single plasma sample obtained 6–8 hr after test dose administration. This ratio was 1.1 in controls and folate deficiency, and 7.8 in patients with pernicious anemia. These plasma measurements are rapidly obtained and may furnish diagnostic information regarding possible intrinsic factor deficiency when quantitative results are equivocal or specimen collection is inadequate.