My Husband Has Been Having Trouble With Sun Exposure For

My husband has been having trouble with sun exposure for the last 8-10 yrs...right now he has these clear fluid blisters that pop up on arms,hands,shoulders, when they bust...they become open areas that look like burn....our Dr has him off work..( he is a roofer, construction) has him on steroid therapy to heal the areas...it has helped but I know prednisone decreases the immune system.. it looks like 2nd and 3rd degree burns...what kind of tests should be done to check for Lupis?