Enzyme abnormalities are frequently found in the red cells of patients with various acquired blood disorders. In leukaemias, preleukaemic states and bone marrow insufficiencies with or without sideroblastosis, changes in enzyme activity are usually characterized by the coexistence of deficiency of some enzymes and an increased activity of others.

The most frequently decreased activities are those of pyruvate kinase, phosphofructokinase,2,3-diphosphoglycerate mutase and adenylate kinase; the most frequently increased activities are those of hexokinase, aldolase, enolase, 6-phosphogluconate dehydrogenase and glucose-6-phosphate dehydrogenase.

In primary myelofibrosis and in polycythaemia rubra vera, enzyme deficiencies are infrequent and differ from those observed in leukaemias and related disorders. Phosphohexose isomerase and phosphoglucomutase deficiencies seem relatively specific for polycythaemia rubra vera.

Explanations for the acquired enzymopathies are still at the stage of hypothesis. The theory of multiple genetic damage may explain some findings but has not yet been proved right. The possibility of post-translational molecular modification is suggested as a working hypothesis.