It is common to see outpatients with “two-to-one half” labs. Is it important to get vaccinated? This is a common concern, so I will give you an answer. The so-called “two-to-half”, hepatitis B serum marker test, containing two antigens, three antibodies, because the HBc antigen is generally difficult to detect the laboratory, only check the antibody, known as “two-to-half”. Anti-HBc is positive, which is the last marker. Detection of anti-HBc alone (anti-HBc positive, but HBsAg and anti-HBs negative), to determine its significance must also be combined with the local prevalence of HBV, China is considered to be a medium-high HBV risk area, the most common reasons are: previous HBV infection, especially in the early stages of life infected with acute hepatitis B, HBs antigen (epitope antibody) disappeared, anti-HBs appears, but over time, the anti-HBs low gradually declines to undetectable levels, while anti-HBc remains in the body due to its long half-life, and the risk of developing cirrhosis or HCC in these populations who are already free of HBV infection is equal to that of those without HBV infection. It is also seen in patients who have been infected with HBV for decades and who present with loss of HBs antigen (epitope antigen) at the end of the natural history of HBV, and these patients usually have low levels of HBV DNA (20-200 IU/mL, which is more common in patients who are ANTI-HBs-negative (as compared to ANTI-HBs-positive patients)). These patients are in fact still hepatitis B patients, only showing HBs antigen negativity, and are still at risk of progression to hepatocellular carcinoma, with liver cancer incidence similar to that of inactive chronic HBV-infected patients (with undetectable HBV DNA), who tend to be born in populations with a high prevalence of HBV, HIV, or HCV infection. In the third scenario, newer, more specific anti-HBc detection tests have not been adopted clinically, and false-positive test results may occur with anti-HBc, especially in populations in low-prevalence areas who are not at risk for HBV infection. Early anti-HBc enzyme-linked immunoassay and radioimmunoassay tests are less specific and more likely to produce false-positive results. In the fourth scenario, the window period of acute hepatitis B, anti-HBc may be the only marker of HBV infection; these populations should be tested for anti-HBc IgM, and HBV-DNA. In the last scenario, there also exists a mutation of HBsAg that results in a lack of expression of HBsAg and false-negative test results, which require examination of HBV DNA. Due to the second of the above mentioned scenarios, the fifth scenario exists where current HBV infection possibility, i.e., there is a risk of blood HBV transmission, blood donors, organ transplant donors, should be routinely screened for anti-HBc, and for patients with HIV infection, or receiving HCV treatment, or immunosuppressive therapy, there may be a risk of HBV reactivation if anti-HBc is already present, and therefore, should be screened for anti-HBc. Therefore. The vast majority of people who are positive for anti-HBc do not have detectable HBV DNA, especially in older people. It should be emphasized that for pure anti-HBc positivity, further testing for other marker tests reflecting hepatitis B infection, such as anti-HBc IgM, anti-HBe, and HBV DNA, is required (using a sensitive test, COBAS). Detection of HBV DNA implies infectiousness; however, a negative HBV DNA result does not completely rule out low levels of HBV DNA. in addition, repeat anti-HBc testing can be performed, especially in blood donors, and a negative anti-HBc on a follow-up test indicates that the initial test result was a false-positive. there is a high degree of variability in the reporting of anti-HBc positivity, which is dependent upon the sensitivity and specificity of the anti-HBc test, and the HBV prevalence in the study population. when anti-HBc is positive but HBsAg negative, the risk of HBV reactivation is extremely low, and the risk of reactivation still exists when chemotherapeutic agents, or immunosuppressive drugs, are used alone or in combination. Therefore, the risk of HBV reactivation should be considered for all patients (with or without anti-HBs) who are anti-HBc positive in this setting. For those who are ANTI-HBc positive and ANTI-HBs negative, they should be vaccinated against hepatitis B. Hepatitis B vaccination does not cause ANTI-HBc positivity. A minority of anti-HBc-positive patients show recall responses to hepatitis B vaccination, and the vast majority respond to hepatitis B vaccine at a rate similar to that seen in patients who are completely negative for HBV serologic markers.