Implementation of plate reader-based indooxine and Nessler protocols for monitoring L-asparaginase serum activity in childhood acute lymphoblastic leukaemia.

Monitoring the blood serum activity of L-asparaginase in children with acute lymphoblastic leukaemia (ALL) has been highly recommended to detect enzyme inactivation that can cause relapse and to avoid unwanted toxicity. Nevertheless, perhaps at least partially due to the lack of clinically approved commercially available kits or standardized and independently reproduced and validated in-house protocols, laboratory assay-based determination of the optimal doses of L-asparaginase is not carried out routinely. In this study, we adapted previously published protocols for two plate reader-based colorimetric methods, indooxine and Nessler, to measure asparaginase activity. Mock samples with dilutions of the enzyme for initial optimization steps, and patient samples were used as a proof of principle and to compare the two protocols. For the first time the indooxine and the Nessler methods are adapted for a plate reader and L-asparaginase serum activity levels are compared by both protocols. Passing-Bablok and Bland-Altman's statistical analyses found very little difference, strong correlation (