What Does it Mean to Get a False Positive for Hepatitis C?
Hepatitis C Virus (HCV) is one of the most common viruses in the world. HCV causes liver disease and cirrhosis. HCV infection may cause cirrhosis or liver cancer. Most cases are caused by sharing needles with someone who has hepatitis C. There are two types of HCV: 1) Hepatitis C virus type 1 (HCV-1), which is the main cause of chronic hepatitis; 2) Hepatitis C virus type 2 (HCV-2).
A person infected with either type of HCV will have symptoms similar to those caused by other viruses such as flu, colds, chicken pox, etc. However, these infections do not usually lead to death due to antiviral treatment.
The most common symptom of HCV infection is jaundice, which occurs when the body’s white blood cells become overactive and produce too much bilirubin. Bilirubin builds up in the liver and causes yellowing of skin and eyes.
Other symptoms include fatigue, nausea, vomiting, abdominal pain, diarrhea and weight loss. These symptoms are often mistaken for some other condition such as viral hepatitis or bacterial endocarditis (heart attack).
Once infected with type 1 or type 2 HCV, a person is likely to develop long-term (chronic) infection. The rate of acute infection with either type of HCV does not differ much.
In fact, it is very common for an individual to be infected without even manifesting any symptoms. The virus stays in the body even after all the symptoms have disappeared. It can take years for the body to develop antibodies against the virus. Meanwhile, there is no sign or symptom of disease and the person is considered healthy. Unfortunately, someone with a long-term (or chronic) infection may develop problems ranging from liver cancer or cirrhosis, to liver failure and death.
It is important to remember that not everyone infected with HCV develops a chronic infection. In fact, most people fight off the virus and develop antibodies against it.
These people are called acute HCV infection. Some people have a relatively mild infection that also leads to a quick recovery from the disease.
The window period is the time between the initial infection and the detection of antibodies against the virus by laboratory tests. It can last from 1 to 6 months (average: 3 months).
During this period, infected people do not feel sick at all. They may feel some general weakness or feel sick after intense exercise.
For patients with acute hepatitis C, testing for anti-HCV (antibody to HCV) is recommended within 6 months of exposure (i.e.
the time that has elapsed since the last possible instance of contact with the virus). It consists in testing an blood sample for the presence of anti-HCV. If this test comes out positive, it means that a patient has fought off the virus and developed antibodies against it. If it comes out negative, patients are considered to have active infection with HCV and should be tested again after 3 months since the last possible exposure to the virus (as it could still take up to 3 months for the body to develop anti-HCV antibodies).
In short, if your blood test comes out negative for anti-HCV, you can be certain that you do not have an acute infection with the virus. If, however, the blood test comes out positive for anti-HCV, it does not necessarily mean that you have an acute HCV infection.
It could also be that your body is still in the process of fighting off the virus and has not yet developed antibodies against it. In this case, you should get tested again in 3 months to see if your blood tests continue to show the presence of anti-HCV or if they instead start showing the absence of this antibody.
Note: Patients whose first blood test comes out negative but whose second blood test (performed 3 months after the possible exposure to the virus) comes out positive are also considered to have an acute HCV infection. For these patients, additional ALT and HBeAg tests are recommended.
The idea is to determine whether the infection is recent (acute) or old (confirmed). For example, a negative anti-HCV blood test performed right after a potential exposure to the virus does not necessarily mean that the person has not been infected.
It could simply mean that the body has not had enough time to produce antibodies against the virus. As a general rule, HCV antibodies have an approximate latency of 3 months after the infection.
Once a person has been infected by the virus, it takes time for his immune system to produce anti-HCV antibodies. This means that for 2/3 of the people infected by the virus, it takes at least 6 weeks between the moment of infection and the moment their tests turn positive.
In rare cases, however, it can take up to 3 months for the body to produce anti-HCV antibodies.
In short, if your blood test comes out positive and you were exposed to the virus within the last 6 weeks, there is a chance that you may not have developed an acute infection with the virus. In this case, getting retested in 3 months (i.e.
once anti-HCV antibodies should be present in your body) is recommended.
On the other hand, if your first blood test comes out positive and you were exposed to the virus more than 6 weeks ago, it is highly probable that you have an acute HCV infection. If this is your case, you should get tested for both ALT and HBeAg.
The ALT (alanine aminotransferase) test measures a type of enzyme produced by the liver. Higher than normal levels of this enzyme may be caused by various conditions, including liver diseases such as hepatitis C.
A normal ALT level is less than 35 IU/L.
The HBeAg test measures the presence of the “HBeAg” antigen, a substance that is present in the blood only during an active infection with the virus. A positive HBeAg test means that the virus is genetically “acute”, meaning that it has recently infected the individual (i.e.
in the last 6 months). A negative HBeAg test means that the infection is “chronically” present in the body and that it must be at least 6 months old.
The ALT and HBeAg tests are used to identify acute or chronic hepatitis C.
The combination of a positive anti-HCV test and negative ALT and HBeAg blood tests is also considered an indicator of an acute infection with the hepatitis C virus.
If your initial blood test is negative for both anti-HCV and ALT, but you are experiencing symptoms similar to those of hepatitis, your doctor may suggest a follow-up blood test after 6 months.
The following factors may affect the accuracy of the blood tests for hepatitis:
If you are infected by the hepatitis C virus but the blood test comes out negative, it simply means that your body has not had enough time to produce “anti-HCV” antibodies. In other words, it does not necessarily mean that you are not infected.
This can happen, for example, if you have an acute rather than a chronic infection. In this situation, retesting after three months may yield a different result.
Hepatitis C is extremely common in some countries and in some areas of the world. If you are at risk, getting tested on a regular basis makes sense.
Follow-up testing is also recommended for people who have previously had a negative result and might have been exposed to the virus more recently. This includes, for example, healthcare workers after accidental needle sticks.
Tests are available to measure the amount of the virus genetic material (RNA) in your blood (see below). The higher the level of viral RNA, the greater the likelihood that you will develop chronic liver disease or liver cancer in the future.
However, the vast majority of people with chronic hepatitis C infection will never develop liver cancer.
As yet, there is no vaccine to prevent hepatitis C infection.
The hepatitis C antibody test detects the presence of antibodies directed against the hepatitis C virus. The test is not a “true” test for the virus itself because no tests can detect the actual virus itself in your body.
Tests can only look for antibodies, which are part of your immune system’s response to a virus infection.
It takes the body about 6 months to produce these antibodies so this is why a negative test at 6 months does not mean you do not have the virus. The hepatitis C virus can be detected in the blood within the first 2 to 4 weeks of infection although it may take up to 6 months before anti- HCV is detectable in the blood.
The most common reason for getting a false positive result for the anti-HCV antibody is previous infection with another type of “hepatitis” virus. For example, if you had a hepatitis A infection within the last 6 months, you may get a false positive result.
This is because these viruses are similar enough to cause cross-reactions in the test.
As already mentioned, a negative anti-HCV antibody test after 6 months does not necessarily mean that you do not have the virus. A new version of the test can detect the genetic material (RNA) of the hepatitis C virus in your blood.
If this test comes back positive, it is very likely that you are in fact infected with hepatitis C.
The NASBA test (NAT-amphiphilic aciD derived test) detects the presence of the genetic material of the hepatitis C virus (RNA).
This test can distinguish between active viral infection and past infection. The test can also detect infection within the first 2 to 4 weeks after exposure.
Sources & references used in this article:
Hepatitis C virus antibodies in chronic active hepatitis: pathogenetic factor or false-positive result? by IG McFarlane, HM Smith, PJ Johnson, GP Bray… – The Lancet, 1990 – Elsevier
Multiple false-positive serologic tests for HIV, HTLV-1, and hepatitis C following influenza vaccination, 1991 by WR Mac Kenzie, JP Davis, DE Peterson, AJ Hibbard… – Jama, 1992 – jamanetwork.com
Definition of false-positive reactions in screening for hepatitis C virus antibodies by M Schröter, HH Feucht, P Schäfer… – Journal of clinical …, 1999 – Am Soc Microbiol
Diagnostic tests for hepatitis C by DR Gretch – Hepatology, 1997 – Wiley Online Library
Polyarteritis nodosa and hepatitis C virus infection by P Cacoub, F Lunel-Fabiani… – Annals of Internal …, 1992 – acpjournals.org
