Final answer:
The first indicator of a Hepatitis B infection is the Hepatitis B surface antigen (HBsAg), which can be detected in the bloodstream before symptoms appear.
Step-by-step explanation:
The classic first indication of a Hepatitis B infection is the presence of Hepatitis B surface antigen (HBsAg) in the blood. When a person is infected with the Hepatitis B virus (HBV), HBsAg is the earliest marker that appears in the bloodstream, even before symptoms become apparent. This is because HBsAg is a component of the viral envelope, which is released during the replication of the virus. Therefore, the correct answer to the question is C. HBsAg.
Concerning other hepatitis viruses, Hepatitis delta virus (HDV) is a unique virus that can only infect an individual who is already infected with HBV, essentially piggybacking on a pre-existing HBV infection. For general laboratory testing, when liver function is compromised, elevated levels of certain enzymes and bilirubin can be detected in the blood, suggesting the need for comprehensive testing for hepatitis viruses.