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A high white blood cell count, also known as leukocytosis, typically indicates an infection or inflammation in the body. White blood cells are crucial components of the immune system, and their primary function is to fight off pathogens like bacteria, viruses, and other foreign invaders. When the body detects an infection or inflammatory process, it releases more white blood cells into the bloodstream as a response to help combat the issue. This elevation is a common laboratory finding in various conditions, including respiratory infections, urinary tract infections, and inflammatory diseases.

While dehydration, allergic reactions, and stress responses can also affect white blood cell counts, they are not specific indicators like infection or inflammation. In dehydration, for instance, the serum concentration of white blood cells may appear elevated, but it is not due to an increase in their actual production. In allergic reactions and stress responses, the body may exhibit changes in the composition of white blood cells, but these responses do not typically lead to a significant increase in their overall count. Thus, a high white blood cell count most reliably points to an ongoing infection or inflammatory process.