Simultaneous Absorption Test of Human Intrinsic Factor (IF) Bound ⁵⁷Co-vitamin B₁₂ (B₁₂) and Free ⁵⁸Co-B₁₂

Abstract

A urinary B₁₂ excretion test by dual isotope technique was performed in 22 patients including 7 with pernicious anemia, 3 with total gastrectomy and 2 with chronic renal failure. The urinary excretion rate of ⁵⁸Co-B₁₂ was 21.3±3.7% in control group and 4.1±2.6% in both patients with pernicious anemia and those with total gastrectomy. The ratio of ⁵⁷Co-B₁₂ to ⁵⁸Co-B₁₂ was significantly high (p<0.01), ranging 1.4 to 9.4 in the patients with IF deficiency. In this group, percent excretion of ⁵⁸Co-B₁₂ was greater than that of free B₁₂ only when administrated to the same patient.
Free IF was not found in the solution of IF bound ⁵⁷Co-B₁₂ and 8 to 15% of ⁵⁷Co-B₁₂ was proved free from IF by coated charcoal method. It was showed that the exchange of ⁵⁷Co-B₁₂ on IF with free B₁₂ occurred depending on pH and temperature in vitro. Therefore, the higher urinary excretion of the free form of B₁₂ in the dual isotopic method was probably due to the exchange of two forms of B₁₂ in vivo.
The radioactivity of ⁵⁸Co-B₁₂ in 2 ml of urine is too low to be measured accurately. This was settled by counting ⁵⁸Co-B₁₂ adsorbed on uncoated charcoal from 20 ml of urine.