Hepatitis B virus DNA is the most direct, specific and sensitive indicator of hepatitis B virus infection, and HBV-DNA is positive, which shows that HBV is reproducible and infectious. The higher the HBV-DNA, the more severe the virus replication and the more contagious it is. The persistent replication of hepatitis B virus is the root cause of hepatitis B, and the treatment of hepatitis B is mainly antiviral therapy, the fundamental purpose of which is to inhibit virus replication and promote the negative transformation of hepatitis B virus DNA.
The genome (dna) of hepatitis B virus is a circular structure surrounded by two helical DNA strands. One of the longer negative chains forms a complete ring; The other short positive chain is semi-cyclic. After the liver cells are infected, this semicircular DNA chain will be extended with the negative chain as a template under the action of the catalyst-hepatitis B virus DNA polymerase, and finally a complete ring will be formed. At this time, the genome of hepatitis B virus formed a completely circular double-stranded dna. That is, the formation of * * * valence closed-loop DNA (cccDNA) seems to be regarded as the original template for virus replication. After the template is formed, it is easy to copy new virus genes according to the shape of the template. Viral genes will use one of cccDNA as a template to copy one gene after another by using hepatocyte genes and enzymes in DNA polymerase to form negative and positive chains. Finally, they are assembled together to form a new hepatitis B virus DNA. The persistent replication of hepatitis B virus in host hepatocytes is the main determinant of chronic HBV infection. HBV*** valence closed-loop DNA (HBV cccDNA) is an intermediate form in the process of virus replication, with an average of 5-50 copies per infected liver cell and a half-life of 65,438+04.5 years. HBV cccDNA can not only transcribe 3.5kb pre-genomic mRNA, but also transcribe viral mRNA and translate it into viral proteins including HBsAg, which is the most specific indicator of HBV replication level. However, it is difficult to monitor the level of HBV cccDNA in patients' liver tissue by liver biopsy. Serum HBV DNA level is closely related to infectivity and disease progression. It is the most direct and reliable sign of virus replication and the "gold standard" for evaluating HBV replication at present. HBV DNA detection is the only laboratory detection index that can help diagnose occult HBV infection and occult chronic hepatitis B. The quantitative detection of HBV DNA is very important for the diagnosis of chronic HBV infection with atypical serology and for determining the carrying status of inactive HBsAg (serum HBV DNA).
Different stages of chronic infection have obviously different virological characteristics, host immune response and liver pathological damage. Quantitative detection of HBV DNA in laboratory is helpful to determine the status of infected people, and it is very important to determine whether to carry out antiviral treatment and choose the appropriate antiviral treatment scheme.
The immune tolerance period is characterized by active virus replication. Laboratory tests show that the HBV DNA load of infected people's peripheral blood is high, usually higher than 20000 IU/mL( 1x 105 copy /mL, the same below). Serological tests showed that HBsAg and HBeAg were positive, ALT of infected people was normal or only slightly increased, and liver histopathology was normal or only slightly inflamed.
During the immune clearance period, laboratory tests showed that HBsAg was continuously positive, and ALT increased continuously or intermittently. HBV DNA in peripheral blood remains at a high level, usually higher than 20,000 iu/ml, or fluctuates. During this period, most chronic HBV infected people are HBeAg positive. HBeAg positive indicates that the virus has high replication and strong infectivity, and can be diagnosed as chronic hepatitis B with HBeAg positive. About 66% or more patients with HBsAg inactivity will have HBeAg seroconversion. Laboratory examination showed that HBsAg remained positive, but HBeAg disappeared, anti -HBe was positive, virus replication remained low, the viral load in peripheral blood was below 2000 IU/mL or could not be detected, ALT was within the normal range, and liver biopsy showed no obvious inflammatory reaction. During the reactivation period, laboratory tests showed that ALT increased intermittently, the liver had active inflammatory reaction, and the serum HBsAg continued to be positive, which could be anti -HBe positive or HBeAg positive. The viral load of peripheral blood can be less than 2000 IU/mL. However, if the pre-C/C region is mutated, HBeAg expression is down-regulated or not expressed. At this time, although HBeAg is negative, HBV is still in a high replication state, and high viral load can still be detected in peripheral blood.
Every year, about 1% of inactive HBsAg carriers can spontaneously clear HBsAg during the recovery period of hepatitis B. Laboratory tests show that serum HBsAg is negative, anti -HBc and anti -HBs antibodies are positive, and HBV DNA can not be detected in serum, which is called subsided hepatitis B. Because most chronic HBV infected people in China are infected in infancy, naturally recovered hepatitis B is rare.
In occult HBV infection, HBsAg in serum is negative, but HBV DNA can be detected in peripheral blood or liver tissue.
Table 1 helps to determine the laboratory detection indexes and significance of different infection stages.
The 5-year mortality rates of chronic hepatitis B, compensated cirrhosis and decompensated cirrhosis were 0%~2%, 14%~20% and 70%~86% respectively. Liver disease related to chronic hepatitis B is the main cause of death caused by HBV infection. There are more than 300,000 cases of liver cirrhosis and liver cancer caused by HBV infection in China every year. Therefore, we should actively intervene and treat chronic hepatitis B. The overall treatment goal of chronic hepatitis B is to inhibit or eliminate HBV for a long time, reduce the inflammatory necrosis and hepatic fibrosis of hepatocytes, delay and prevent the progress of diseases, and reduce and prevent the occurrence of liver decompensation, cirrhosis, HCC and its complications, thus reducing mortality and improving quality of life. The treatment of chronic hepatitis B mainly includes antiviral, immunomodulation, anti-inflammatory, liver protection, anti-fibrosis and symptomatic treatment, among which antiviral treatment is the most critical. Antiviral therapy mainly achieves the above goal by inhibiting HBV replication for a long time. Antiviral therapy is mainly used for patients with active chronic hepatitis B in immune clearance period and reactivation period. Therefore, first of all, it is necessary to determine the suitable patients and treatment opportunities for chronic hepatitis B through reliable laboratory diagnosis such as quantitative detection of HBV DNA, and accordingly determine the appropriate treatment plan. In addition, monitoring virological response through quantitative detection of HBV DNA during treatment is of great significance for judging antiviral efficacy, adjusting clinical antiviral treatment scheme and prognosis.
At present, there are two kinds of drugs for treating hepatitis B: one is common interferon α and pegylated interferon α, and the other is nucleoside (acid) analog. Interferon can enhance immunity and antivirus, and some patients can get lasting response after a certain course of treatment. It has been reported that the HBsAg clearance rate of HBeAg-positive chronic hepatitis B patients treated with long-acting interferon can reach 3%~ 10%. The rate of HBsAg disappearance or serum negative conversion in patients is higher than that of nucleoside (acid) analogues, but interferon drugs have adverse reactions, which limit its wide application in clinic. Nucleoside (acid) analogues can inhibit virus replication by inhibiting reverse transcription process, which has a strong inhibitory effect on virus, but they can not clear HBV cccDNA in liver cells in a short time, and the recurrence rate is high after drug withdrawal. It has always been thought that the clearance rate of HBsAg in the treatment of chronic hepatitis B with nucleoside (acid) analogues is low and it is difficult to be used as the end point of treatment. However, in recent years, with the continuous optimization and improvement of clinical antiviral treatment schemes, the HBsAg clearance rate of chronic hepatitis B has been improved through continuous antiviral treatment with nucleoside (acid) analogues, and some reports can reach 6%.
The quantitative detection of HBV DNA is not only used for the diagnosis of chronic hepatitis B, but also the HBV DNA load in patients' peripheral blood is an important index to decide whether to carry out antiviral treatment. Almost all countries' guidelines for the prevention and treatment of chronic hepatitis B suggest whether to start antiviral treatment according to the viral load. The quantification of serum HBV DNA is an important index to determine the indication of antiviral treatment. For patients with HBeAg positive chronic hepatitis B, patients with HBV DNA ≥20 000 IU/mL and active liver inflammation (ALT increased, or liver inflammation index ≥G2 found by liver biopsy) should be treated with antiviral therapy. Patients with HBeAg-negative chronic hepatitis B often have a long medical history and long-term accumulation of lesions. The annual incidence of liver cirrhosis is 8%~ 10%, which is higher than that of HBeAg positive chronic hepatitis B (2%~5%). Therefore, the treatment of HBeAg negative chronic hepatitis B should be actively carried out. When HBVDNA ≥2 000 IU/mL is accompanied by liver active inflammation, antiviral therapy should be started.
The decrease of serum HBV DNA level is an important basis for judging the effect of antiviral treatment and an important index of response-oriented treatment. Therefore, the baseline level should be detected before treatment, and once the treatment is started, it should be detected every 3~6 months to dynamically monitor the changes of HBV DNA level, and at the same time detect ALT, HBeAg and anti-HBe. The therapeutic roadmap of nucleoside (acid) analogues mainly depends on the quantitative detection of HBV DNA to determine the virological response, which is very important for judging the curative effect, prognosis and drug resistance, and is an important basis for optimizing and adjusting the treatment plan. If the level of HBV DNA is effective in the treatment of nucleoside (acid) analogues, the same drugs will continue to be treated; Otherwise, the failure of treatment should be combined with treatment. Among them, if the absolute level of serum HBV DNA is lower than 60 IU/mL after 24 weeks of treatment, it is a complete virus response and the same drug treatment can be continued; More than 60 IU/mL but less than 2 000 IU/mL is a partial reaction, and whether to adjust it should depend on the specific drugs selected. After 24 weeks of treatment, the patient's serum HBV DNA level was higher than 2 000 IU/mL, which means that the response was insufficient.