Effect of methotrexate on the deoxyuridine suppression test: results with different cell preparations

Recently, the deoxyuridine suppression test was used to detect folate deficiency. Several cell preparations were used in this test, and the sensitivity of the test seems to vary with them. We used whole blood (micro-dU test) and bone marrow cells for the deoxyuridine suppression test, and the effects of methotrexate were compared. [3H]Thymidine incorporation into DNA was highest when the concentration of methotrexate was 1 microM in the whole blood culture and bone marrow culture. Methotrexate concentrations from 100 nM to 1 mM did not affect the results of the micro-dU test. However, the bone marrow deoxyuridine test became abnormal with methotrexate, and the abnormality in test values was corrected by the addition of N5-formyltetrahydrofolate. Differences in the results between the micro-dU test and the bone marrow deoxyuridine suppression test seem to represent specificity of each dU test.