Hi.I Am Searching For A Reason That My Husband's Doctor

Hi.I am searching for a reason that my husband's doctor is checking for bleeding by doing a endoscopy and a colonoscopy to find out if there is something bleeding inside. My husband hasn't shown blood when passing stool or coughing up any. I would like to know how they will find out the problem if these tests don't show anything? Wondering what other tests they could do?