Final answer:
An increase in leukocytes would be seen in a patient's blood work following a diagnosis of infection, as they are part of the immune response.
Step-by-step explanation:
When a patient's blood work comes back with a diagnosis of an infection, we expect to see an increase in leukocytes. This condition is known as leukocytosis and is a typical response to infection, as leukocytes are the white blood cells responsible for fighting off pathogens. In contrast, erythrocytes (red blood cells), thrombocytes, and platelets are not directly involved in the immune response to infections; erythrocytes transport oxygen, while thrombocytes and platelets (which are the same thing) play a role in blood clotting and repair of blood vessels.