Final answer:
A white blood cell count over 11,000 cells per microliter usually indicates an infection, with specific types of WBCs such as Neutrophils and CD4+ T cells being key indicators of systemic infections or immunodeficiencies like HIV.
Step-by-step explanation:
An elevated white blood cell count (often denoted as WBC count) typically suggests that an infection is present in the body. In general, a WBC count over 11,000 cells per microliter of blood is usually indicative of an infection, although the normal range varies with age and gender. It's important to note that WBCs are comprised of different cell types, such as lymphocytes, neutrophils, monocytes, eosinophils, and basophils, each with their specific roles within the immune response. The presence of infection is often associated with Neutrophilia, an increase in the number of neutrophils. Furthermore, in certain clinical scenarios, such as in the case of Olivia from the provided clinical focus scenario, a high WBC count of 28.5 K/µL was observed, which far exceeds the normal range and is indicative of a systemic infection.
Deterioration in health conditions, such as HIV, can result in significantly lowered CD4+ T cell counts, dropping below 400 per microliter in patients who cannot mount an effective immune response, compared to a healthy person's count of about 1,000 per microliter. Besides absolute counts, percentages of particular WBC types are relevant. In Olivia's case, the neutrophil percentage was recorded as 60%, which is higher than the normal range of 23-45%, further confirming the presence of an infection.