Which condition can be physiological or pathological, characterized by an increase in white blood cells?

Leukocytosis is characterized by an increase in white blood cells and can occur under both physiological and pathological conditions. Physiologically, leukocytosis can happen during times of stress, exercise, or pregnancy as the body responds to various stimuli that demand greater immune activity. Pathologically, it may indicate infections, inflammatory diseases, or even hematological malignancies.

The definition of leukocytosis embraces its role in signaling that the body's immune system is actively responding to challenges, making it a key marker in clinical assessments. This distinguishes it significantly from other options. For instance, leukopenia, which indicates a decrease in white blood cells, would not involve an increase but rather a compromised immune response. Anemia pertains to a deficiency in red blood cells or hemoglobin and does not directly relate to white blood cell counts. Thrombocytopenia refers to a low platelet count, which is unrelated to the white blood cell levels as well. Thus, leukocytosis stands out as the condition reflecting an increase in white blood cells, making it the correct choice.