The myeloproliferative disorders. Current clinical and laboratory considerations.

The various hemopoietic and supportive cells of the marrow may proliferate beyond physiologic boundaries in response to a number of stimuli. In certain instances, the stimuli are known, and upon their removal the myeloproliferation returns to normal boundaries. These, the reactive myeloproliferations, are best represented by the leukemoid states and the secondary polycythemias. In other cases, the stimuli responsible for the myeloproliferation remain unknown and the clinical disease ends fatally. These, the neoplastic myeloproliferations, include the granulocytic, monocytic and red cell leukemias, as well as the polycythemia vera and myelofibrosis syndrome. In clinical practice it is important to identify the various myeloproliferative syndromes. This task has been facilitated by cytochemical tests that have recently become available, among which the estimation of the leukocyte alkaline phosphatase (LAP) in peripheral blood is a technically simple and extremely useful example. The LAP is normal in secondary polycythemias and decidedly elevated in polycythemia vera, myelofibrosis and leukemoid states. It is greatly decreased in the granulocytic leukemias.