In the presence of pneumonia, how high can the white blood cell count typically rise?

In cases of pneumonia, the white blood cell count (WBC) often rises significantly as the body responds to infection. A typical range for the increase in WBC count due to pneumonia can indeed reach between 15,000 to 22,000 cells per microliter of blood. This elevated level reflects the immune system's activation as it works to fight off the infectious agents responsible for the pneumonia, which can include bacteria, viruses, or other pathogens.

In this context, the increase in WBC count is primarily due to the proliferation of neutrophils, which are the first responders in the immune response to bacterial infections, and lymphocytes, which are more involved in viral infections. A count within this range indicates a robust immune response to the infection, providing insights into the severity and systemic nature of the pneumonia. Higher counts can also imply more severe infections or complications such as sepsis.

The other options indicate lower ranges, which generally would not align with the expected leukocytosis seen in pneumonia cases. While variations can occur based on individual patient factors and the underlying cause of pneumonia, the 15 to 22 thousand range is well-documented as typical for this condition.