Individually, NUDT15 c.415C > T had a sensitivity and specificity of 57.9 and 94.0%, respectively, (OR = 21.45, 95% CI 5.94–77.41, p < 0.001) in predicting thiopurine-induced leukopenia while NUDT15 c.52G > A were only observed in patients with leukopenia. This evidence concerns the gene NUDT15 and Decreased total leukocyte count.