The 2018 AASLD HBV Guidelines recommend testing of persons who are HBsAg‐positive at risk for HDV, including those with HIV infection, persons who inject drugs, men who have sex with men, immigrants from areas of high HDV endemicity, and patients who are HBsAg‐positive with low or undetectable HBV DNA but high alanine aminotransferase (ALT) levels. The gene discussed is GPT; the disease is HIV infectious disease.