Rapid diagnosis and characterization of acute promyelocytic leukaemia in routine laboratory practice.

The rapid diagnosis of the t(15;17)(q22;q21) promyelocytic leukaemia is important in the early introduction of targeted therapy with all-trans retinoic acid plus chemotherapy. It has been noted that these are usually myeloperoxidase (MPO)-positive and HLA-DR-negative with homogenous expression of CD33 and heterogeneous expression of CD13. We evaluated the use of immunophenotyping, morphology and cytogenetics in our own practice. Cascade testing, using cytoplasmic MPO expression in a high percentage of blast cells in bone marrow as the primary screen and PML (promyelocytic leukaemia protein) expression as the secondary confirmatory test, allowed rapid identification of the cases with t(15;17). This approach allows early instigation of appropriate therapy.