Hepatitis testing encompasses two types of laboratory assays; immunoassays and nucleic acid amplification testing (NAAT). A detailed description of the many different types of immunoassays and amplification testing systems used by clinical laboratories is outside the scope of this short course. Instead, we will briefly discuss two specific types of immunoassay that are commonly used in viral hepatitis testing, the EIA and CIA.
Immunoassays are laboratory detection tests that employ antibodies to capture and detect target antigens within specimens. Conversely, they can also use antigens to capture a specific antibody that is present in the specimen and then quantitates the amount of antibody present. Once the specific binding has occurred, wash steps ensue and remove excess reagents. A biochemical reporter system (light production, a color change, or even the presence of radioactivity) can then be used to quantify the amount of analyte present in the specimen.
NAAT uses the polymerase chain reaction (PCR) sequence to amplify a specific DNA sequence that can then be detected using detection probes. In the case of RNA viruses, reverse-transcriptase PCR (RT-PCR) is used to first amplify and then detect and quantify viral RNA. In the context of hepatitis, NAAT is used primarily for the quantitation of HCV RNA. Monitoring HCV viral load (the amount of viral RNA in the patient's serum) is a vital tool in the treatment of chronic HCV infection.