There are several tests for diagnosing HBV infection; the tests monitor either viral load or liver function.
Tests for HBV Viral Load. Quantification of HBV DNA in the blood by polymerase chain reaction (PCR) or newer real-time PCR tests are indicative of the activity of HBV replication. Levels above 2000 IU/ml indicate active or chronic infection, while levels below this indicate inactive carriage of the virus (Chevaliez 2012).
Serum hepatitis B surface antigen (HBsAg) level is also a marker of infected liver mass and the amount of HBV DNA in infected hepatocytes. When combined with PCR testing, a blood test for HBsAg levels can be used to monitor progression of chronic HBV infection or identify inactive carriers (Chevaliez 2012).
Other serological tests for viral load include quantification of HBeAg, a marker for high-infectivity HBV, as well as the detection of antibodies to HBV antigens (anti-HBs, anti-HBe, and anti-HBc, an antibody to the HBV core antigen), which can indicate a prior or chronic infection (WHO 2009; Chevaliez 2012). Testing for anti-HBc IgM antibody can identify acute HBV infection (Gitlin 1997).
Liver function tests. There are several blood tests that are not specific to HBV and nonspecifically assess liver function, but are important in the diagnosis of infection; these include ALT (alanine aminotransferase, a marker of liver cell damage), bilirubin (an indicator of liver excretion function), and albumin levels & prothrombin time (indicators of liver synthesis function) (Liaw 2009). Most of these markers can be measured in routine blood tests. Fibrometers (ie, liver-fibrosis-specific blood panels), which combine some of these markers with other liver-specific markers, are also available (Castera 2012).
Liver biopsy. Liver biopsy is an important, but invasive technique for grading liver damage. Newer non-invasive methods use imaging techniques to assess liver stiffness (a direct physical property of the liver that increases as the liver is filled with connective tissue during fibrosis). These include transient elastography (an ultrasound technique) and magnetic resonance elastography (Castera 2012).