leukocyte alkaline phosphatase (LAP), an enzyme present in lymphocytes that is elevated in various diseases such as cirrhosis and polycythemia and in certain infections. It is measured in the blood to detect these disorders and to differentiate chronic myelogenous (myelocytic) leukemia from leukemoid reactions. Normal amounts of this enzyme in a smear of fresh venous blood are 50 to 150 units. Also called neutrophil alkaline phosphatase.
