Hepatitis C antibodies and antibody testing
What are antibodies?
Antibodies are our main form of defence in the bloodstream. They are a form of protein that is produced in response to anything foreign that gets into our bloodstream — such as viruses, bacteria, or vaccines.
Antibodies are mostly limited to the humeral spaces — an almost medieval term for body fluids which are outside the actual cells of the body. These include blood, milk and other body fluids.
What do antibodies do?
Basically, antibodies stick to anything foreign that they find. The processes involved in a virus entering a body cell are complex, and having big globs of protein (antibody) hanging off a virus can be enough to block their attempted entry to cells.
This is particularly true if there are a lot of antibodies around — and if they recognise different parts of a virus and cover the surface of it.
As well as the passive function of sticking to viruses, some antibodies trigger a series of events which result in inflammation of the area around a cell area, making it generally inhospitable to bacteria and viruses.
Are antibodies killer cells?
No, but cruising around in our bloodstream are ‘killer’ cells called macrophages. When they bump into a cell or substance in the bloodstream, they need some kind of signal to determine whether they should engulf and destroy it — or whether it’s a part of the body. When a foreign body in the bloodstream has antibodies stuck to it, the killer cells take it as a signal that it is something to be destroyed.
Why don’t macrophages destroy HCV?
The hepatitis C virus (HCV) is a master of disguise. As it reproduces, it often changes its appearance ever so slightly. It’s a process called mutation and means the virus confuses our HCV antibodies and macrophages, remaining one step ahead of them. Although we quickly eradicate lots of hepatitis C viruses once they’re identified, there are always others which have mutated, and are not recognised as effectively and survive.
How do the HCV antibody tests work?
HCV Antibody tests are used to see if a person has hepatitis C (also called hep C). Doctors commonly use this test to determine if their patients have come into contact with HCV.
If the test comes back positive, it means that HCV antibodies were found — proof that the virus must have entered the body at some point in time.
If people are able to clear the virus, they still keep their antibodies. A positive antibody test doesn’t always mean someone has the virus, although in most cases the person does have it.
To confirm whether a person has hep C or not, a PCR test is usually performed. These tests look for presence of the actual hep C virus.
What is the ‘window period’?
Once a virus enters the body it takes a period of time before antibodies are produced. Thus, an antibody test carried out too soon following infection might return a false negative result.
With HCV, it takes up to 6 months to be sure the antibody test will return an accurate result and this is called the HCV antibody window period.
The window period for confirming a hep C diagnosis has been reduced dramatically following introduction of HCV RNA (often called PCR) testing. The window period for these tests is 4 weeks.
Last Reviewed: 01 May 2007
