Important clinical and prognostic features of childhood acute lymphoblastic leukaemia are determined by the degree of residual leukemic cells in a patient’s blood or bone marrow during the initial phase of treatment. This persistence of these cells is referred to as Minimal residual Disease (MRD). The usefulness of monitoring of MRD in children with acute leukaemia has provided meaningful information for decision based practice such as treatment response and risk of relapse. There have been several methods used to monitor MRD. Morphological assessment alone may be inaccurate because, in most cases, leukemic blasts may be difficult to distinguish from lymphoid precursors.
MRD assays should be accurate, specific, rapid and technically feasible. The two most useful techniques are Flow Cytometry for leukaemia-associated immunophenotypes and Polymerase Chain Reaction of antigen-receptor gene rearrangements. Compared to the morphological screening of bone marrows alone, these two methods enable clinicians to determine, more precisely, the risk of relapse and hence determine patient outcome.