Author: Liu Wenjuan
Unit: Department of Clinical Laboratory, Xiyuan Hospital, China Academy of Chinese Medical Sciences
Recently, some patients have found positive HCV antibodies (HCV-Ab) during screening for infectious diseases, and tested for hepatitis C nucleic acid (HCV-RNA) to exclude hepatitis C infection, and the results are negative. Doubts have been raised about the accuracy of the HCV antibody test results.
What exactly is the relationship between the two? Does a positive HCV antibody necessarily infect hepatitis C?
1. What is hepatitis C?
Viral hepatitis C, referred to as hepatitis C and hepatitis C. It is a viral hepatitis caused by hepatitis C virus (HCV) infection, which is a global epidemic and is one of the common chronic liver diseases.
According to the World Health Organization, the global infection rate of HCV is about 3%, and there are about 35,000 new cases of hepatitis C every year. The prevalence of hepatitis C in mainland China is 1.3%.
Without appropriate antiviral therapy after infection, 20% to 30% of people infected with hepatitis C will develop cirrhosis after 10 to 20 years, and 2% to 7% will progress to primary liver cancer.
Most patients with hepatitis C infection have atypical early symptoms, no obvious clinical symptoms, and most patients are insidiously infected. The main modes of transmission are: blood transfusion transmission, sexual transmission, mother-to-child transmission, etc.
The main mode of transmission of hepatitis C
Hepatitis C antibody
Hepatitis C antibody is an antibody produced by the human immune system after the hepatitis C virus enters the body, so it is also a marker of the body's infection with hepatitis C virus.
Because the hepatitis C virus is particularly highly variable, the production of hepatitis C antibodies is not as protective as hepatitis B antibodies and is a marker of hepatitis C virus infection. But there are two possibilities for this infection, one is that it has been previously infected or treated, and there is no virus in the body, but it leaves a mark of infection, just like the arm has been cut, leaving a scar. The other is that the hepatitis C antibody is positive, and the hepatitis C virus is also positive, which is a hepatitis C patient and needs treatment.
Therefore, it can be seen that hepatitis C antibody is a marker after human infection with hepatitis C virus, which is lifelong, not easy to remove, but harmless to the body. However, whether it is a hepatitis C patient also depends on whether there is hepatitis C virus in the body.
Hepatitis C RNA
Hepatitis C virus (HCV) is a single-stranded positive-stranded RNA virus with a cystic membrane. A positive HCV RNA indicates that the virus replicates in vivo; a negative HCV-RNA indicates that the virus has been cleared. The hepatitis C virus RNA test is the detection of the actual presence of the hepatitis C virus in the blood.
Relationship between hepatitis C antibodies and hepatitis C virus
The hepatitis C virus enters the body and is recognized by the body to produce antibodies. Therefore, in general, the body should first appear the virus and then the antibodies appear. As immune recognition increases, immune aggression ability establishes, and part of the hepatitis C virus is automatically eliminated (if it is not eliminated for more than half a year, the possibility of re-elimination is less likely).
Map of changes in hepatitis C antibodies and hepatitis C virus after infection
Therefore, there is no strict correlation between hepatitis C antibodies and hepatitis C virus. Because some patients have hepatitis C virus in the blood intermediate, there are peaks and troughs in the process, so the virus appears temporarily negative. It should be repeatedly tested, more than half a year negative, to be truly negative, but the antibody is always present.
2. Laboratory tests for hepatitis C
Hepatitis C antibody (HCV-Ab) test
Hepatitis C antibody (HCV-Ab) testing is currently the most commonly used detection technique in clinical practice. It is mainly used for clinical screening.
But the method does not tell whether the infection is new (in the acute phase) or long-term (chronic), or has been cured. Antibody tests sometimes have "false negatives" and "false positives", so they should be determined based on the condition and in combination with other tests.
False positive
The main reasons for the false positive include: the presence of high concentrations of non-specific IgG or rheumatoid factors in the blood adsorbed to solid-phase carriers or coated antigens; interference with superoxide dismutase in the samples examined; and impurity of HCV antigens used to prepare reagents.
Window period
The window period is long, and it usually takes more than 40 days from HCV infection to detectable antibodies (window period). Anti-HCV negative does not exclude the possibility of carrying HCV and being infectious, so the quality of detection reagents still needs to be improved and improved.
Missed or false positive
Due to the different quality and proportion of HCV gene recombinant antigens used by various manufacturers, there are certain differences in the sensitivity and specificity of reagents of various manufacturers, resulting in inconsistencies in the HCV-Ab test results, resulting in missed tests or false positives.
Hepatitis C nucleic acid (HCV-RNA) test
Clinical nucleic acid testing for hepatitis C virus uses molecular biology methods to check for the presence of a virus in the blood. The advantage of this method is that the results are more objective, but the price is also more expensive. PCR technology is currently the most sensitive and specific detection technology in the field of molecular biology. It can greatly shorten the window period of detection from 70 days of antibody appearance to 1-2 weeks.
Window period for HCV antibody detection
It is of great significance for early diagnosis and blood screening; it is a powerful supplement to HCV antibodies when serological tests are unclear or serological indicators do not match clinical findings, and is often used as the main means of diagnosing HCV infection. It can not only know whether there is a hepatitis C virus, but also determine the amount of the virus, thus providing a basis for the condition and the effectiveness of treatment.
Combined application of HCV-Ab and HCV-RNA detection
The results of HCV-Ab and HCV-RNA testing can be applied in combination with four patterns, as shown in Table 1:
Significance of the results of the combined detection of HCV-Ab and HCV-RNA tests
Note: HCV-Ab and HCV-RNA cannot be used to determine the severity of disease or to predict prognosis and progression of disease.
3. Precautions for hepatitis C antibody testing
Pay attention to diet before performing hepatitis C antibody testing
Hepatitis C patients must pay attention to their diet before the hepatitis C antibody test, it is best to choose some light and easy to digest food, it should be noted that patients must not drink alcohol, for those spicy and irritating foods should be strictly prohibited, so as not to increase the burden on the liver, resulting in inaccurate test results, which may affect the treatment and prognosis of patients.
Do not take the drug until the hepatitis C antibody test
In the hepatitis C antibody test as far as possible to avoid taking drugs, because after the drug enters the human body, it needs to be detoxified by the liver's metabolism, if the drug is taken before the test, it is likely to increase the burden on the liver, thus affecting the accuracy of the test results.
Fasting before hepatitis C antibody testing
Before the hepatitis C antibody test, be sure to ensure that you are fasting eight hours in advance, that you cannot eat, and that you should drink less water. Otherwise, it is likely to affect the test results and not accurately reflect the patient's specific condition.
Source: Laboratory
Edited by: Yeah Reviewer: Xiao Ran