Final answer:
A urinalysis would be ordered to evaluate the client's flank pain, as it can indicate kidney involvement in systemic lupus erythematosus.
Step-by-step explanation:
The nurse would anticipate that a urinalysis would be ordered to evaluate the client's flank pain. Flank pain in a client with systemic lupus erythematosus (SLE) can indicate kidney involvement, such as lupus nephritis. A urinalysis can help identify signs of kidney inflammation or damage, such as the presence of proteinuria, red blood cells, or white blood cells in the urine.