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Abnormal body weight, usually defined as more than 20 percent above average for age, height and bone structure.
A blockage in the GI tract that prevents the flow of liquids or solids.
Occult Bleeding
Blood in stool that is not visible to the naked eye. 
Opportunistic infection
An infection caused by an infectious agent that would  not cause a healthy person sick.
Orthostatic Hypotension
Drop in blood pressure upon standing; may lead to light-headedness or fainting.
Oral Hypoglycemic Agents
Drug that lowers the level of glucose (sugar) in the blood. The pills work for some people whose pancreas still produces some insulin. 
Loss of calcium and other substances from bones, causing bones to become weak and prone to fractures.