Which of the following is a factor that can influence white blood cell counts?

White blood cell (WBC) counts can be influenced by a variety of factors, making the answer "all of the above" a comprehensive choice.

The age of the individual plays a significant role in WBC counts, as different age groups may have varying normal ranges. For instance, infants typically have higher WBC counts than adults, reflecting the active immune development in early life.

Dietary habits can also impact WBC counts. Nutrition plays a critical role in immune function, and deficiencies or specific diet types could lead to changes in WBC levels. For example, inadequate intake of certain vitamins and minerals can impair immune response, potentially affecting WBC production.

Finally, the presence of infections is one of the most direct influences on WBC counts. In response to an infection, the body produces more white blood cells, particularly neutrophils, as part of the immune response to help fight off pathogens. This elevation is often used in clinical settings to indicate infection or inflammation.

Given these factors, selecting "all of the above" acknowledges the multifaceted nature of influences on white blood cell counts, highlighting that age, dietary habits, and infections can all play contributory roles in variations observed in WBC levels.