A 24-year-old man came to the emergency depament with a broken leg. A blood test revealed his WBC count to be 22 x 103/ml. Five hours later, a second blood test revealed values of 7 x 103/ml. What is the cause of the increased WBC count in the first test?

The majority of WBCs are stored in the bone marrow, waiting for an increased level of cytokines to stimulate their release into the circulation. However, trauma to bone can result in a release of WBCs into the circulation. This increase in WBC count is not primarily due to any inflammatory response, but instead is attributed to mechanical trauma and associated stress responses.