Viral hepatitis, an inflammation of the liver often caused by viruses like Hepatitis A, B, and C, can progress silently for years without noticeable symptoms. Laboratory testing is the only way to accurately diagnose an infection and determine its stage. The diagnostic process involves a combination of blood tests that look for the body’s immune response, the presence of the virus itself, and any resulting damage to the liver. Understanding these tests helps doctors create a personalized management plan.
What Diagnostic Tests Look For
Hepatitis testing is designed to identify the body’s reaction to the virus and the virus itself. The immune system responds by producing specialized proteins called antibodies. Detecting these antibodies indicates that a person has been exposed to the hepatitis virus, suggesting a past or current infection, or immunity from a vaccine.
Tests also target the virus’s physical components, known as antigens. Antigens are proteins on the surface of the virus, and their presence in the bloodstream is a direct sign of an active infection. A third approach involves searching for the actual genetic material of the virus, which is its ribonucleic acid (RNA) or deoxyribonucleic acid (DNA).
Initial Screening Blood Tests
The first step in diagnosis involves screening blood tests, focused on detecting current or previous infections with Hepatitis B (HBV) and Hepatitis C (HCV). For Hepatitis B, the initial test looks for the Hepatitis B Surface Antigen (HBsAg). A positive HBsAg result indicates the virus is currently present in the body and the person is infectious.
Screening for Hepatitis C begins by testing for the Hepatitis C antibody (anti-HCV). This antibody test determines if a person has ever been exposed to the virus, but follow-up testing is required to confirm if the virus is still actively replicating. Hepatitis B diagnosis often includes testing for the core antibody (anti-HBc) and surface antibody (anti-HBs) to determine a person’s full immune status, including immunity from vaccination or past recovery.
Confirming Active Viral Infection
When an initial screening test (HBsAg or anti-HCV) is positive, a second, more specific test is needed to confirm the presence of an active, replicating virus. This confirmation is achieved using molecular techniques, primarily Nucleic Acid Testing (NAT), often performed via Polymerase Chain Reaction (PCR). These tests directly search for and amplify the viral genetic material, either HBV DNA or HCV RNA.
The results are reported as the “viral load,” which measures the number of viral particles in the blood. A high viral load confirms an active, ongoing infection. This quantitative measurement guides decisions about when to start antiviral treatment and how to monitor its effectiveness. For Hepatitis B, viral DNA is a marker of active replication, while for Hepatitis C, the presence of HCV RNA is necessary to diagnose a current infection.
Measuring the Impact on Liver Health
The diagnostic process assesses the extent of damage the virus has caused to the liver. Liver Function Tests (LFTs) are a standard blood panel that measures enzymes like Alanine Aminotransferase (ALT) and Aspartate Aminotransferase (AST). Elevated levels of these enzymes suggest that damaged or inflamed liver cells have released their contents into the bloodstream.
Non-invasive imaging techniques evaluate chronic liver damage. Elastography, performed using ultrasound or specialized Magnetic Resonance Imaging (MRI), measures the stiffness of the liver tissue. Scar tissue (fibrosis) makes the liver stiffer, and the degree of stiffness correlates with the severity of the scarring. This technology has largely replaced the invasive liver biopsy traditionally used to stage the progression of fibrosis and cirrhosis.
Doctors also use non-invasive scoring systems, such as the Fibrosis-4 (FIB-4) index, which combines results from blood tests like ALT, AST, and platelet count with the patient’s age. These scores estimate the amount of liver scarring, helping to identify patients who may have advanced fibrosis or cirrhosis.