DPYD and dihydropyrimidine dehydrogenase deficiency: Indeed, patients with gastrointestinal cancer have impaired renal function due to pre-existing conditions of loss of fluids, thus reducing the accuracy of plasma uracil concentration as form of DPD activity assessment: a large retrospective French study [21] showed that 12.7% of Caucasians had uracilemia greater than 16 ng/mL, suggesting that the phenotypic approach might overestimate the diagnosis of DPD deficiency.