L-asparagine is measured using HPLC and reported in µmol/L.
L-asparaginase is measured as enzyme activity with units of IU/L.
Measurement of L-asparagine in plasma can be difficult in a patient receiving L-asparaginase since the enzyme may continue to function in vitro (after specimen collection) unless the specimen is immediately frozen or the enzyme is otherwise inactivated.
Goal of therapy:
(1) depletion of L-asparagine (to unmeasurable levels)
(2) trough L-asparaginase activity above the target cutoff (usually the recommended level is > 100 IU/L. but L-asparagine depletion may occur at trough levels < 50 IU/L)
Measurement of L-asparagine or L-asparaginase may be helpful:
(1) to confirm adequate dosing
(2) after long-term use to confirm efficacy
(3) if antibodies to the enzyme are suspected
(4) disease progression despite adequate therapy
