Which of the following is a common cause of leukocytosis?

Leukocytosis refers to an elevated white blood cell (WBC) count, which is often a physiological response to various stimuli in the body. Infection is one of the most recognized causes of leukocytosis because the body’s immune response is activated when pathogens invade. When an infection occurs, the bone marrow produces and releases more white blood cells, particularly neutrophils, to fight off the invading microorganisms. This increase in leukocytes is a critical part of the immune response, helping to detect and eliminate infections.

In contrast, while conditions like bone marrow failure and hemolysis can affect blood cell counts, they typically lead to lower WBC counts or do not result in leukocytosis. Dehydration can cause a relative increase in cell counts due to hemoconcentration but is not primarily considered a direct cause of leukocytosis. Therefore, the association between infection and leukocytosis is well-established in clinical practice, making infection the correct answer as a common cause of elevated WBC levels.