Changes in serum vitamin B ₁₂ levels in patients with megaloblastic anaemia treated with folic acid

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In 21 patients with megaloblastic anaemia associated with the tropical malabsorption syndrome serum vitamin B(12) levels have been measured serially before and during parenteral folic acid therapy. In 11 patients there was a significant rise in serum B(12) levels, reaching a peak three to 17 days after starting the folic acid. In three of these cases, absorption of labelled B(12) was the same before and after the administration of folic acid. In two cases there was a fall in serum B(12) levels and in seven there was no change. In one case small amounts of folic acid produced no change in serum B(12) levels, whereas larger doses produced a prompt but transient rise.