How can I know if my splenectomy scar is getting infected?

Signs of infection. Usually an infection in an incision occurs within a week or two of surgery. Most people have signs like increasing pain and swelling, redness, fever or pus. If you are worried, you should call your doctor. He/she is the best one to determine if you are developing an infection.
Drainage. The telltale sign of a wound infection is purulent drainage ("pus"). Other signs include redness, swelling, a fever, the wound edges separating, and blood-tinged drainage. Many people who undergo splenectomy are taking steroids; this is known to slow down wound healing and may cover up some of the traditional signs of infection described above. When in doubt, go see your surgeon.