Rasburicase and the uric acid measurement

 Q; 42 years old male is transferred to ICU after he developed Tumor Lysis Syndrome (TLS) due to ongoing chemotherapy. Rasburicase is started. The uric acid will be? (select one) 

A) falsely high 

 B) falsely low 

Answer: B 

After the initiation of the Rasburicase, uric acid cannot be followed reliably to evaluate the response. Rasburicase can spuriously lower the uric acid. Rasburicase causes the enzymatic degradation of uric acid at room temperature in the collected sample. 

Ideally, specific orders should be written to collect the blood sample in a pre-chilled tube. Moreover sample should be placed on ice immediately. Rasburicase induced enzymatic degradation occurs over few hours, so the sample should be run STAT within 3-4 hours. Said that even this precaution may not help to have a reliable value (reference #2).

#oncology

#pharmacology

References:

1. Prescribing information for rasburicase available online at http://products.sanofi-aventis.us/elitek/elitek.html (Accessed on September 03, 2021). 

2. Depreter B, Stove V, Delanghe J. Sampling on ice will not yield reliable uric acid monitoring in rasburicase-treated patients. Clin Biochem. 2016 Dec;49(18):1390-1395. doi: 10.1016/j.clinbiochem.2016.04.011. Epub 2016 Apr 27. PMID: 27129796. 

3. Howard SC, Jones DP, Pui CH. The tumor lysis syndrome [published correction appears in N Engl J Med. 2018 Sep 13;379(11):1094]. N Engl J Med. 2011;364(19):1844-1854. doi:10.1056/NEJMra0904569