What is the condition characterized by an increase in the number of leukocytes in the blood?

Leukocytosis is the condition defined by an increase in the number of leukocytes, or white blood cells, in the bloodstream. This rise often indicates an active immune response to various factors such as infections, inflammation, or stress. The body produces more white blood cells to help fight off pathogens or react to other stressors, which results in higher levels being detectable in laboratory tests.

This increase can be physiological, such as after exercise or during pregnancy, or pathological, stemming from diseases like leukemia or other bone marrow disorders. Understanding leukocytosis helps in diagnosing these conditions, as the differential count may provide further insights into the specific reason behind the leukocyte elevation.

The other choices relate to different conditions affecting blood components; however, they do not describe an increase in leukocyte count, making them unrelated to the definition of leukocytosis.