Screening for dihydropyrimidine dehydrogenase deficiency by measuring uracilemia in chronic kidney disease patients is associated with a high rate of false positives.

BACKGROUND:Pretherapeutic screening for dihydropyrimidine dehydrogenase (DPD) deficiency based on the measurement of plasma uracil ([U]) is recommended prior to the administration of fluoropyrimidine-based chemotherapy. Cancer patients frequently have impaired kidney function, but the extent to which kidney function decline impacts [U] levels has not been comprehensively investigated. METHODS:We assessed the relationship between DPD phenotypes and estimated glomerular filtration rate (eGFR) in 1751 patients who benefited on the same day from a screening for DPD deficiency by measuring [U] and [UH2]:[U], and an evaluation of eGFR. The impact of a kidney function decline on [U] levels and [UH2]:[U] ratio was evaluated. RESULTS:We observed that [U] was negatively correlated with eGFR, indicating that [U] levels increase as eGFR declines. For each ml/min of eGFR decrease, [U] value increased in average by 0.035 ng/ml. Using the KDIGO classification of chronic kidney disease (CKD), we observed that [U] values >16 ng/ml (DPD deficiency) were measured in 3.6 % and 4.4 % of stage 1 and 2 CKD (normal-high eGFR, >60 ml/min/1.73 m2) patients, but in 6.7 % of stage 3A CKD patients (45 to 59 ml/min/1.73 m2), 25% of stage 3B CKD patients (30 to 44 ml/min/1.73 m2), 22.7% of stage 4 CKD patients (15 to 29 ml/min/1.73 m2 and 26.7% of stage 5 CKD patients (<15 ml/min/1.73 m2). [UH2]:[U] ratios were not impacted by kidney function. CONCLUSION:DPD phenotyping based on the measurement of plasma [U] in patients with decreased eGFR is associated with an exceedingly high rate of false positives when kidney function decline reaches 45 ml/minute/1.73 m2 of eGFR or lower. In this population, an alternative strategy that remain to be evaluated would be to measure the [UH2]:[U] ratio in addition to [U].