High blood calcium

My husband has just started radiotherapy for lung cancer. He has twice been into hospital because of high calcium in his blood. This was initiated by the hospital. Monitoring of his cancer levels has been passed to his GP. His last two blood tests have shown his calcium level to be 2.9 and 2.98. The GP is just going to do another blood test. These levels are higher than when he was taken into hospital to have a saline drip. He does not want to go into hospital but I am worried about how dangerous his level is.