Different composition of the eosinophilic bone marrow pool in reactive eosinophilia and eosinophilic leukaemia.

The composition of the eosinophilic cell series in the bone marrow has been analysed in 10 patients with a pronounced reactive eosinophilia (RE) and in 2 with eosinophilic leukaemia (EL). An imparied differentiation of the eosinophils was found in the EL patients compared with the RE group. Thus the ratio of eosinophilic promyelocytestmyelocytes: segmented eosinophils was 9.2 and 9.1, respectively, in the patients with EL and 0.1--3.1 (average 1.3) in the RE patients. It is suggested that EL is characterized by an impaired differentiation of the eosinophilic bone marrow cells and that the recognition of this abnormality is of value in the diffential diagnosis between EL and RE.