Sampling on ice will not yield reliable uric acid monitoring in rasburicase-treated patients

A phase II study to evaluate the efficacy of low-dose rasburicase (1.5mg) in adolescent and adult acute leukemia and high-grade lymphomas with tumor lysis syndrome

The FDA recommended dose of rasburicase 0.2 mg/kg/day till the resolution of TLS or up to 5 days, might be in excess and is prohibitively expensive. The quality of evidence supporting low dose rasburicase is limited. The objective is to study the plasma uric acid response rate. This is a single center, non-randomised phase II study. Duration is 10 June 2017 till 30 July 2019. Study setting is at Adult Hematolymphoid Unit, Tata Memorial Center. Participants are patients with acute leukemia and high-grade lymphomas aged >/=18 years, with ECOG PS of 0-3, with either laboratory or clinical TLS. Rasburicase was administered at fixed-dose of 1.5 mg. The subsequent doses (1.5 mg each dose) were administered only if plasma UA levels did not decline by >50% on day 2, at the physician's discretion. We demonstrate that a low-dose rasburicase strategy leads to rapid and sustained reductions of uric acid in about 52% patients.

Acid freezes uricolysis in addition to glycolysis: Utility of fluoride-EDTA-citrate tube in the measurement of uric acid for patients administered rasburicase

BACKGROUND

In samples from patients administered rasburicase, ex vivo uricolysis leads to spuriously low uric acid results. The manufacturer's recommendation of storing the sample in ice-water until analysis, however, does not fully arrest uricolysis. Since uricase activity is affected by pH and metal chelators, we assessed uricolysis inhibition in sodium fluoride-ethylenediaminetetraacetic acid (EDTA)-citrate sample tube (FC Mix tube, Greiner) used primarily for plasma glucose.

METHOD

A serum pool was spiked with rasburicase and uric acid measured at 15, 45, 90, 150, 240 and 1080 min in a lithium heparin tube in ice-water, plain tube at room temperature (RT), EDTA tube at RT, FC Mix tube in ice-water, FC Mix tube at RT and FC Mix tube at RT prepared by dissolving FC Mix in serum.

RESULTS

The rate of urate decay was lowest in the FC Mix tube independent of temperature, then lithium heparin tube in ice-water, then EDTA tube at RT and highest in the plain tube at RT. Uric acid concentrations in the prepared FC Mix tube at RT and heparin tube in ice-water were, respectively, 98.2% and 93.8% of control values at 90 min, 97.1% and 89.3% of control values at 4 h, and remained higher in the prepared FC Mix tube at all time points.

CONCLUSION

NaF-EDTA-citrate mixture largely arrested rasburicase mediated ex vivo uricolysis without the need for sample cooling. We propose that sample tubes containing NaF-EDTA-citrate be used for the measurement of uric acid in patients administered rasburicase.