Leukocytosis - an increase in the number of leukocytes in the blood of more than 10,000 in 1 μl, or 10 • 109 / l. Occurs as a result of increased leukocytopoiesis or redistribution of leukocytes in the body. There are physiological and pathological leukocytosis; physiological include alimentary leukocytosis (after eating), myogenic (after physical stress), leukocytosis of pregnant women and others. Pathological leukocytosis is caused by the reaction of hematopoietic organs to irritation caused by infectious, toxic, inflammatory, radiation and other agents. It is also observed in necrosis of the tissue (myocardial infarction, disintegration of the tumor), after major bleeding, wounds, head injuries, etc. As a rule, the leukocytosis disappears along with the cause of it. Transient leukocytosis, characterized by the appearance in the blood of immature leukocytes, is called a leukemoid reaction.
In most cases, there is an increase in the number of neutrophils, that is, neutrophilic leukocytosis is observed, often with a shift to the left in the leukocyte formula. Eosinophilic leukocytosis (eosinophilia) is noted in many allergic diseases (bronchial asthma, serum sickness), helminthic invasions, pruritic dermatoses, etc. Lymphocytosis (marked increase in the number of lymphocytes in the blood) occurs in some infectious diseases and intoxications. Monocytic leukocytosis (monocytosis) is detected in subacute septic endocarditis, malaria, rubella, syphilis, etc. The presence of leukocytosis is determined by counting certain types of leukocytes - leukocyte formula.