Hair ball is a common problem for cat owners. It is hard to differentiate from other causes of vomiting and gagging by routine tests which would cost money . It is recommended to brush your cats hair at least once a day for short hair breeds and twice a day for medium hair and long hair breeds. Brushing would also prevent hair hairmatts on the body which can promote skin problems. There are oral products like Laxatone that would help to pass the hair balls through the poop. Good Luck, Dr.Amir Khosravani