Impact of renal and hepatic function on dihydropyrimidine dehydrogenase phenotype assessed by enzyme activity in peripheral blood mononuclear cells and uracilemia.

Objectives: To investigate the relationship between uracilemia (U) and dihydropyrimidine dehydrogenase (DPD) activity in peripheral blood mononuclear cells (PBMC) and whether they are influenced by renal or hepatic impairment.

Methods: This retrospective study included 176 cancer patients with pre-treatment U (UPLC-MSMS assay) and PBMC-DPD (radioenzymatic assay) analyzed the same day (routine phenotyping). Blood renal (creatinine, BUN) and hepatic (ALT, AST, GGT, ALP, albumin, bilirubin) work-up was performed within 15 days before or up to 4 days after DPD phenotyping. Biochemical markers were categorized according to CTCAEv5.0 grade (G). Glomerular filtration rate (eGFR) was estimated (CKD-EPI and EKFC). Non-parametric statistical tests were used.

Results: Prevalence of partial deficiency was 3.4 % based on PBMC-DPD (i.e. ≤100 pmol/min/mg) and 6.3 % based on U (i.e. ≥16 μg/L). No complete deficiency was observed. Fifteen patients out of 176 (8.5 %) exhibited discordant DPD status between PBMC activity and U. The correlation between PBMC-DPD and U was significant but weak (r= -0.309, p<0.001). PBMC-DPD (mean 246, median 235, range 62-926 pmol/min/mg prot) was not influenced by renal or hepatic impairment. U (mean 9.6, median 8.5, range 1.7-57.8 μg/L) was significantly higher in patients with elevated BUN (normal vs. >1-UNL, p=0.009), GGT (G0 vs. G1 vs. G2 vs. G3, p<0.001), AST (G0 vs. G≥1, p=0.015), or with hypoalbuminemia (G0 vs. G ≥ 1, p=0.045). Categorized creatinine or eGFR did not influence U.

Conclusions: It remains unclear whether renal and/or hepatic impairment acts as a confounding factor affecting the accuracy of uracilemia testing, or whether truly impacts DPD activity, suggesting caution in U interpretation.