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a | Stages observed in individuals with a fully functional immune system aged >5 years, without natural or acquired immunodeficiency. No HBV marker is detectable during the first week (eclipse period) after contact with infectious HBV. The following week (window period) is characterized by HBV DNA as the only marker of infection. Acute infection is characterized by concomitant presence of hepatitis B surface antigen (HBsAg) and HBV DNA for a period of several weeks followed by the development of first anti-hepatitis B core antigen (anti-HBc) then anti-HBs. The complexing of HBsAg and anti-HBs initially makes these two markers undetectable, but HBV DNA and anti-HBc are present during the second window period. Simultaneous detection of anti-HBc and anti-HBs indicates recovery from infection. Over time, anti-HBs levels wane, leaving anti-HBc as the only detectable marker. In 1–5% of cases, very low levels of HBV DNA are detectable, indicating OBI. b | In individuals with immunodeficiencies, the eclipse period as well as window period occur as described above, although infants with vertically acquired HBV carry maternal anti-HBc until 12–18 months of age. Chronic hepatitis B is characterized by simultaneous detection of HBsAg and HBV DNA, followed by anti-HBc. All three markers are carried long term, with levels modulated by seroconversion to anti-hepatitis B e antigen. Over time, some cases reach a point where HBsAg is no longer detectable (below the limit of detection), and the association of anti-HBc and low levels of HBV DNA indicate OBI. OBI, occult HBV infection. | Allain J-P, Opare-Sem O. Screening and diagnosis of HBV in low-income and middle-income countries. Nat Rev Gastroenterol Hepatol [Internet]. 2016 Sep 14 [cited 2017 Apr 13];13(11):643–53. Available from: http://www.nature.com/doifinder/10.1038/nrgastro.2016.138