Like "This does happen every now and again. You've nicked a blood vessel and it created the bruise. How have your BG's been? If they are running as usual, you can assume that the bruise is not blocking or impeding delivery of insulin and can opt to leave it in place if it is not painful or uncomfortable. If your BG's are running higher,, your insulin absorption is being affected. In the latter case, I would change out my set early."