Early diagnosis of acute hepatitis-B infection is made by-

After a person is infected with HBV, the first virologic marker detectable in serum within 1-12 weeks, usually between 8-12 weeks, is HBsAg. Circulating HBsAg precedes elevations of serum aminotransferase activity and clinical symptoms by 2-6 weeks and remains detectable during the entire icteric or symptomatic phase of acute hepatitis B and beyond. In typical cases, HBsAg becomes undetectable 1-2 months after the onset of jaundice and rarely persists beyond 6 months. After HBsAg disappears, antibody to HBsAg (anti-HBs) becomes detectable in serum and remains detectable indefinitely thereafter. (Harrison's Principles of internal medicine, 20 th edition, page 2540)