What condition could cause an increase in white blood cell count?

An increase in white blood cell count, or leukocytosis, is commonly associated with infection. The body's immune response to pathogens like bacteria, viruses, or fungi involves the activation and proliferation of white blood cells, which are crucial for defending against infections. When the body detects an invader, the bone marrow produces more white blood cells to help fight off the infection, leading to a measurable increase in the white blood cell count.

Other conditions can affect white blood cell counts, but they do not typically lead to an increase as directly and commonly as infections do. For example, dehydration can cause hemoconcentration, which may superficially raise white blood cell counts, but this is not a true increase in production. Liver disease can influence overall blood cell production and regulation; however, it usually does not lead directly to an increase in white blood cell count. Anemia primarily affects red blood cells and does not directly correlate to elevated white blood cell levels. Hence, infection is the most straightforward and common cause of increased white blood cell counts as it reflects an active response to combat illness.