People often find out they are positive for hepatitis C when they are donating blood or after routine testing reveals mild abnormalities in their liver function tests. To many this information is a great surprise. Some may have engaged in high-risk activity (such as injection drug use with equipment sharing) perhaps twenty or more years ago and breathed a sigh of relief when they tested negative for hepatitis B and HIV, not realizing there was another virus to be concerned about.
A person can have a small amount of blood drawn to test for hepatitis C. The test, called the enzyme-linked immunosorbent assay (ELISA), looks for antibodies that the body makes in response to the hepatitis C virus. When this test was first introduced in 1990, its results were found not to be very accurate. Many people showed a positive test when they were not infected, and some showed a negative result even though they were infected. More sensitive versions of the test became available in 1993. Anyone who was told in the late 1980s or early 1990s that he or she had hepatitis C, especially if there were no obvious risk factors for the disease, should now have another, more sensitive, blood test performed.
Recent infections may not be detected on a blood test, even if the person is having hepatitis symptoms, because 40-50 percent of people with symptomatic acute hepatitis C infection have not yet developed antibody. When a person is diagnosed with acute hepatitis and the blood test is negative for hepatitis C, the test should be repeated in one or two months to confirm that the symptoms were not caused by hepatitis C. Most people test positive on the blood test four to six weeks after infection, although it may take as long as six months.
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