FREE AND INTRINSIC FACTOR BOUND RADIOACTIVE CYANOCOBALAMIN. SIMULTANEOUS ADMINISTRATION TO ASSESS THE SIGNIFICANCE OF LOW SERUM VITAMIN B12LEVELS

摘要

Consistently low serum vitamin B12levels are primarily due to malabsorption of the vitamin from several causes. One hundred and fifty elderly patients with serum vitamin B12levels of 150 pg per ml or less were studied by the simultaneous administration of57Co labelled vitamin B12bound to intrinsic factor and free58Co labelled vitamin B12(Dicopac test). For the diagnosis of pernicious anaemia only 10 ml of urine are required as the result is expressed as a ratio of the excretion of57Co to58Co. Data are presented to suggest that maximal urinary isotope excretion occurs 10–20 hours after oral administration of the isotope and that this is the optimum period in which to collect a 10-ml sample of urine. Forty patients with pernicious anaemia had a57Co/58Co excretion ratio of 1·5 or over. The Dicopac test was considered to be of particular value if the patient had prior vitamin B12therapy or a megaloblastic blood picture with low levels of vitamin B12and folate. The excretion of less than 4 per cent of each isotope for a 24-hour collection was considered a useful parameter of intestinal malabsorption when renal function was normal.In subjects with normal isotope excretion and ratios, the double isotope test did not assist in the elucidation of low serum vitamin B12leve