L-asparaginase Assay for Leukemia Patients

The L-asparaginase assay can help determine if leukemia patients area received the correct dose to reach an therapeutic level.The L-asparaginase assay is a laboratory developed test (LDT) to determine the enzyme activity of L-asparaginase in patients who have been treated with Elspar®/Kidrolase®, Oncaspar®, or Erwinaze®. This assay has been validated and is performed in CLIA certified high complexity laboratory to monitor the asparaginase activity level during a patient’s treatment.

L-asparaginase activity test can help physicians identify patients experiencing “silent inactivation” as well as to ensure that adequate asparaginase activity is present during asparaginase treatment. The assay is done on a serum sample obtained from the patient after treatment. A minimal volume of sample (0.2 mL) is required, and the results are returned overnight.

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What is L-asparaginase?

Acute lymphoblastic leukemia (ALL) is a blood cell cancer characterized by an over accumulation of immature white blood cells called lymphoblasts. These immature cells inhibit the production of normal blood cells and infiltrate to other organs. ALL has an annual incidence of 6000 persons per year and peaks in early childhood. Asparginase, an enzyme produced by bacteria, is used as an anti-neoplastic agent to treat ALL. The mechanism of action is inhibition of asparagine in cancer cells. Asparagine is a non-essential amino acid, meaning that normal cells can produce asparagine through its innate biochemical pathways.

Asparagine is needed by all cells as an important part of its protein structures. Cells without asparagine will die. The immature white blood cell does not have the capacity to manufacture asparagine. In the cancer cells, asparaginase breaks down asparagine and ultimately kills the cells. Asparaginase treatment has been incorporated into many ALL protocols for kids and adults. Like all chemotherapeutic and anti-neoplastic agents, asparaginase is not without side effects. The most common adverse reactions are hypersensitivity and sub-clinical hypersensitivity (silent inactivation). Silent inactivation occurs when patients develop anti-asparaginase anti-bodies without clinical signs of hypersensitivity. These patients suffer greater incidence of cancer relapse. Therapeutic drug monitoring through measurement of asparaginase enzyme activity can identify patients at risk for silent inactivation.

The Testing

The primary goal of Asparaginase therapy is to maintain adequate asparagine depletion. The Asparginase activity assay developed by scientists at Granger Genetics is a therapeutic drug monitoring test that accurately measures the activity level of Asparginase in a patient’s blood. This assay quantitatively measures the activity level of the drug and allows physicians to optimize treatment. Activity levels are determined using a coupled enzymatic assay that ultimately results in decreased absorbance at 340nm. Results are reported within 2 days of sample receipt. Stat testing may be available and should be requested by contacting client services.

How Does It Work?

A minimum of 0.200mL of serum or plasma is needed to run the assay. Asparaginase activity is determined by a coupled enzymatic assay. Aspartic acid formed from asparagine by the action of asparaginase reacts with α-ketoglutaric acid in the presence of glutamic-oxaloacetic transaminase, yielding oxaloacetic acid, which oxidizes reduced β-nicotinamide adenine dinucleotide in the presence of malic dehydrogenase, resulting in a decrease in absorbance at 340 nm. The rate of reaction at 37°C is a linear function of enzyme activity.

E. coli asparaginase purchased from Sigma/Aldrich (St. Louis, MO) is used as the analytical reference standard. Samples with activities exceeding the upper range of the calibration curve are re-assayed after diluting with blank human serum. Assay performance: accuracy was 97.0% of the nominal activity and the precision was 6.0%CV at the lower limit of quantitation (0.025 IU/mL). Quality control samples with asparaginase in serum at activities of 0.0375, 0.075, and 0.115 IU/mL were assayed with a between-day accuracy of 99.1-102.1% and a precision of 4.7-5.8%CV.