Final answer:
Corticosteroids suppress the immune system, which can mask signs of infection, making this the major action the nurse should monitor for in a child taking corticosteroids for systemic lupus erythematosus.
Step-by-step explanation:
The nurse is aware that while corticosteroids are effective in managing conditions like systemic lupus erythematosus (SLE), they can also suppress the immune system. This suppression can lead to an important side effect: the ability to mask signs of infection. Corticosteroids, such as prednisone, work by downregulating the immune system, thereby inhibiting the inflammatory response that is a part of the body's normal defense against infection. Because inflammation is a common sign of infection, reducing this response can make it more difficult to detect when an infection is present.
Corticosteroids do not generally cause bone marrow suppression, significant increase of liver enzymes, or decrease in renal function; these are not considered major actions of these drugs. The risk of infection and its masking is a known and major concern when patients are on corticosteroids, especially at high doses or for prolonged periods.