Perchloric Acid Treatment To Stabilize Uric Acid Concentrations in Blood Samples of Patients Receiving Uric Acid Oxidase (Rasburicase) Therapy

Sample handling requirements for uric acid analysis during recombinant uric acid oxidase (rasburicase, Sanofi-Synthelabo) therapy are a matter of concern. Rasburicase catalyzes the oxidation of uric acid to allantoin, which is easily excreted by the kidney. It is indicated for the treatment and prophylaxis of malignancy- or chemotherapy-associated hyperuricemia (1). For monitoring uricemia in patients receiving rasburicase therapy, the manufacturer recommends keeping blood samples in ice water immediately after collection and during specimen transport until analysis. When samples are maintained at 4 °C, uric acid concentrations are reported to be adequately preserved (2). However, cold inactivation of the enzyme requires a cooling period to bring the collection tube to 4 °C, during which further degradation of uric acid is possible (3). Furthermore, rack-based modern random access analyzers do not allow maintaining the sample temperature at 4 °C. Moreover, in practice, laboratories are often unaware that the patient has received rasburicase because the blood samples were sent at room temperature to the laboratory as part of routine biochemistry testing (2). In view of the rapid uricolysis by rasburicase, the accuracy of uric acid determinations in patients under rasburicase treatment can be questioned under routine conditions.