Differential Diagnosis for HBSAG Negative, ANTI-HBC Positive, ANTI-HBS 1.12

• Single Most Likely Diagnosis
  • Vaccinated Individual: The presence of anti-HBs (antibody to hepatitis B surface antigen) at a level of 1.12, which is considered protective, along with negative HBsAg (hepatitis B surface antigen) and positive anti-HBc (antibody to hepatitis B core antigen), suggests the individual has been vaccinated against hepatitis B. The anti-HBc positivity could be due to a past infection that has been cleared or, less commonly, a false positive, but in the context of vaccination, it's more indicative of vaccine response or past resolved infection.
• Other Likely Diagnoses
  • Resolved Hepatitis B Infection: Individuals who have had a past hepatitis B infection that has been cleared may test positive for anti-HBc and anti-HBs, with HBsAg being negative. The presence of anti-HBs at a protective level supports this diagnosis.
  • Passive Immunity from Hepatitis B Immunoglobulin (HBIG): Although less common and typically seen in specific clinical contexts (e.g., post-exposure prophylaxis), individuals who have received HBIG may temporarily test positive for anti-HBs. However, this would not typically be associated with a positive anti-HBc unless there was also an underlying infection or vaccination.
• Do Not Miss Diagnoses
  • Chronic Hepatitis B Infection with Mutations: Although HBsAg negative, certain mutations in the hepatitis B virus can lead to false-negative HBsAg results. The presence of anti-HBc and anti-HBs could mask an underlying chronic infection, especially if the virus has mutated. This diagnosis is critical to consider due to the implications for liver disease and transmission.
  • Window Period Infection: In the early stages of hepatitis B infection, there can be a "window period" where HBsAg has not yet become positive, and anti-HBs has not yet risen. However, this would typically be associated with the presence of HBV DNA and possibly symptoms, rather than a stable, protective level of anti-HBs.
• Rare Diagnoses
  • Hepatitis B Virus (HBV) Mutations Affecting HBsAg: Certain rare mutations in the HBV genome can affect the production or detection of HBsAg, leading to false-negative results. These cases might present with positive anti-HBc and anti-HBs due to the immune response to the infection.
  • False Positives/Negative Due to Laboratory Error: Although rare, laboratory errors can lead to false-positive or false-negative results. This should be considered, especially if clinical presentation and laboratory results do not align.