Which laboratory finding is indicative of bacterial infection in a critically ill patient?

An elevated white blood cell count (WBC) is indicative of a bacterial infection in critically ill patients because it reflects the body’s immune response to the presence of pathogens. When bacteria invade the body, the immune system reacts by producing more white blood cells, particularly neutrophils, which are key players in combating bacterial infections.

In the context of critical illness, monitoring WBC counts provides valuable information about the patient's infectious status. A significantly elevated WBC count, often accompanied by a left shift (an increase in immature white blood cells), suggests active infection and is a common finding in severe bacterial infections, such as sepsis.

In contrast, low or normal WBC counts can occur in various conditions, including viral infections or immunosuppression, and are not typically associated with an adequate immune response to bacterial pathogens. An elevated platelet count does not directly correlate with the presence of bacterial infection and could indicate other processes like inflammation or tissue injury. Therefore, the elevated WBC count is the most relevant laboratory finding to indicate a potential bacterial infection in critically ill patients.