Mitotic activity in acute promyelocytic leukaemia and leukaemoid reactions

Bone marrow smears from 6 untreated patients with acute promyelocytic leukaemia (APL) and from 6 patients with leukaemoid reactions (LR) have been compared with smears from healthy controls. The mitotic indices of the granulopoietic precursor cells were significantly lower in the APL group and significantly higher in the LR group, both compared with the normals. Mitotic countings seem to be of diagnostic value for distinguishing APL from conditions simulating this disease.