However, before stopping rules for antiviral therapy can be applied, we need to learn more about the kinetics of HBsAg declines during the natural history of the infection and as a

response to therapy so that we can better define the best timing, the relevant HBsAg cutoff levels, and the best ways to apply these rules in clinical practice. (HEPATOLOGY 2011;) The detection of hepatitis B surface antigen (HBsAg) in serum was pivotal to the discovery of hepatitis B virus (HBV) more than 4 decades ago and remains the cornerstone of diagnosis today.1-3 HBsAg seroclearance is considered to be the closest thing to a cure for chronic hepatitis B (CHB): it reflects immunological control of the infection and confers an excellent prognosis in the absence of preexisting cirrhosis or concurrent infections TAM Receptor inhibitor with other viruses.2-6 Not surprisingly, HBsAg seroclearance BVD-523 purchase has attracted considerable attention in both natural history studies and therapeutic trials. The incidence of spontaneous HBsAg seroclearance is low, especially in younger patients. Interferon (IFN)

therapy appears to be able to enhance the rate of HBsAg seroclearance from 0.72% (controls) to 2.25% per year in European patients and from 0.07% to 0.43% per year in Asian patients.6 A greater understanding of the factors influencing HBsAg levels might enable us to improve this still further. Recently, a wealth of new data on HBsAg quantitation has emerged, and it is becoming apparent that information on HBsAg levels can add to our understanding of both the natural history of the disease and its response to therapy. This is a good time to review and discuss issues concerning the clinical utility of HBsAg quantitation and the ways in which this may help us with patient management in the future. ALT, alanine aminotransferase; anti-HBe, antibody DCLK1 to hepatitis B e antigen; cccDNA, covalently closed circular DNA; CHB, chronic hepatitis B; ETV, entecavir;

HBeAg, hepatitis B e antigen; HBsAg, hepatitis B surface antigen; HBV, hepatitis B virus; HCV, hepatitis C virus; IFN, interferon; LAM, lamivudine; LdT, telbivudine; NA, nucleos(t)ide analogue; NPV, negative predictive value; PEG-IFN, pegylated interferon; PPV, positive predictive value; TDF, tenofovir. Our understanding of the pathogenesis and natural history of CHB has been facilitated by technological advances that have improved the sensitivity of both serological assays for quantifying antigens (including HBsAg) and polymerase chain reaction assays for measuring HBV DNA. Several independent groups have compared HBsAg and HBV DNA levels during different phases of the disease, and their findings have been rather consistent. To put these findings into context, we must consider the HBsAg production pathway and the ways in which this is related to serum HBV DNA levels and intrahepatic covalently closed circular DNA (cccDNA). HBsAg is produced by more than one pathway (Fig.