deoxyuridine suppression test . New micro method for

The deoxyuridine suppression (dU) test measures the effect of deoxyuridine in suppressing the uptake of radioactively labelled tritiated thymidine into DNA and is specifically abnormal in vitamin B12 or folate deficiency, or when the metabolism of these is disturbed. The test is based on the observation that bone marrow cells from patients deficient in vitamin B12 incorporated much more thymidine into DNA after prior exposure to deoxyuridine in vitro than normal cells.' This is also true for folate deficient cells and can be corrected by incubation in vitro with either vitamin B12 or folate, as appropriate.2 The deoxyuridine suppression test has proved valuable in the diagnosis of megaloblastic anaemia. Abnormal results are specifically found only in disorders of vitamin B12 or folate metabolism, and in most cases the addition of vitamin B12 and folic acid in vitro gives a clear distinction between vitamin 312 and folate deficiency,3 and results relate well to the severity of the haematological changes and results of microbiological assays of vitamin B12 and folate.5 Examples of its contribution as an analytical method include showing that the effect of nitrous oxide is to inactivate intracellular vitamin B12.6 The micro method of the deoxyuridine suppression test was developed to reduce the amount of bone marrow and reagents required for each individual marrow culture by a factor of 10: to simplify the preparation of the cells for scintillation counting; and to permit more exhaustive studies with limited material.