A positive CRP blood test typically indicates inflammation throughout the body, according to MedlinePlus. When a person is healthy, tests do not find CRP, or C-reactive protein, in the blood. Increased levels are caused by many conditions, including cancer, heart attack, inflammatory bowel disease, pneumonia, rheumatoid arthritis, lupus and tuberculosis.
Although positive CRP results suggest inflammation, they do not diagnose a specific disease or reveal the precise location of a problem, MedlinePlus explains. In addition to looking for general inflammation, doctors use CRP tests to monitor the performance of anti-inflammatory drugs and search for recurrence of diseases, such as rheumatoid arthritis and lupus. The test is not foolproof, however, because these diseases sometimes do not increase CRP levels.