Myeloperoxidase-deficient polymorphonuclear leucocytes. (II) Longitudinal study in acute myeloid leukaemia, untreated, in remission and in relapse.

Myeloperoxidase (MPO) activity of blood granulocytes was estimated in 96 cases of acute myeloid leukaemia (AML), in 35 patients obtaining complete remission and in 14 of these patients during later relapse. As the pretreatment value of MPO activity was the same in patients who died before obtaining remission as in patients obtaining complete remission, determination of MPO-deficient PMN has no prognostic value with respect to the probability of obtaining complete remission. While half of the untreated patients had increased numbers of MPO-deficient PMN in the blood, all patients in complete remission had normal MPO activity (P = 0.0002). A normalization of the MPO activity after induction therapy, therefore suggests remission. Positive correlations could be demonstrated between an initially abnormal MPO activity and abnormal activity at relapse as well as between an initially abnormal MPO activity and normal activity at relapse (P = 0.0004). It is concluded that determination of the % of MPO-deficient PMN in the blood, may be a useful indicator of complete remission in AML, and in serial determinations during the remission phase also an indicator of threatening relapse.