In which condition does LAP show the least activity?

LAP, or leukocyte alkaline phosphatase, is an enzyme found in certain types of white blood cells, particularly neutrophils. The activity of LAP can vary significantly based on the condition affecting the bone marrow and blood cell production.

In chronic myelogenous leukemia (CML), there is a proliferation of myeloid cells that generally present with immature granulocytes. These immature cells demonstrate lower levels of LAP activity compared to mature leukocytes. This diminished activity is a distinguishing feature of CML and assists in differentiating it from other conditions, such as leukemoid reactions where there is typically an increase in LAP due to the heightened activity of mature neutrophils responding to infection or stress.

In contrast, leukemoid reactions, polycythemia vera, and idiopathic myelofibrosis would typically exhibit higher LAP activity. Both leukemoid reactions and idiopathic myelofibrosis can lead to increased LAP levels due to the presence of more mature neutrophils in response to either infection or an increase in hematopoietic activity. Polycythemia vera, being characterized by increased red blood cell production, can also lead to elevated LAP levels, as there’s an overall increase in myeloid lineage activity.