A multimodal approach for diagnosing patients with acute promyelocytic leukaemia

A practical and efficient multi-modal protocol for processing specimens for patients referred with a question of acute promyelocytic leukaemia (APL) is described. The initial analysis comprises haematological evaluation of the bone marrow and peripheral blood smears using Romanowsky-stained slides. Concomitantly, a sample is processed for direct preparation as well as 1- and 2-day unstimulated cultures using conventional cytogenetic techniques. Communication between the cytogenetic and haematological laboratories is of critical importance so that the optimal conditions for culture (i.e. longer term versus unstimulated overnight and direct preparations) for the cytogenetic detection of chromosome rearrangements can be selected. The likelihood of detecting the characteristic translocation of APL, t(15;17), is enhanced in a longer term culture versus unstimulated overnight and direct preparations. Fluorescent in situ hybridization (FISH), utilized as an adjunct to GTG-banding, was found to be a powerful technique for detecting the t(15;17), especially where the GTG-banded preparation was of suboptimal quality. Results of five recent representative cases of APL are described to illustrate a practical approach which can be adapted by any clinical pathology laboratory.