HCV Diagnostic testing
SIGN's recommendations on diagnostic testing for HCV and an overview of the evidence that supports them.
Principles of testing
Detection of viral RNA by nucleic acid tests (NAT, usually using reverse transcription polymerase chain reaction; RT PCR) indicates current infection. Detection of antibodies indicates resolved or current infection. The testing algorithm suggested in Figure 1 is based on the following key principles:
- diagnostic assays are most reliable when used on plasma or serum 19 2++
- assays for antibody in saliva are very sensitive if optimum salivary collection devices and modified enzyme linked immunosorbent assays (ELISA) are used, but NAT for viral RNA is unreliable 19-21 2++
- limited testing of dried blood spots for detecting antibody has suggested it may be useful but further evaluation is needed for the detection of viral RNA 19 2++
- nucleic acid testing sensitive enough to detect 50-100 IU/ml of virus must be performed to detect current infection 22 2+
- viral RNA can be detected as early as one to two weeks after infection, whereas antibody can be detected at seven to eight weeks after infection 23 4
- antibody to infection may not be generated particularly if the individual is immunosuppressed 24 4
- following acute infection, HCV RNA may oscillate between positive and negative for several months. Results from samples taken at this time may be misleading. 23 In an individual positive for HCV antibody, but negative for HCV RNA, a second sample should be tested to confirm the initial diagnosis, especially as the date of infection is unknown in most cases 4
- individuals with a positive HCV antibody test and repeatedly negative RNA do not require further active management of hepatitis C infection 24 4
- since hepatitis C is a serious communicable disease, after an initial laboratory diagnosis, a second sample should be taken from the patient to confirm correct identification of the original sample 25 4
- genotyping of individuals with proven HCV infection is required to determine likely response to treatment. Those with genotype 1 infection require longer duration of treatment than those with genotype 2 and 3 (see section 9.1.2) 7 1++
- expert guidance suggests that healthcare workers who have, or might have, sustained an occupational exposure to HCV should be offered RNA testing at 6, 12 and 24 weeks, with anti-HCV testing at 12 and 24 weeks. 26 4
Diagnostic testing for HCV should be performed on serum or plasma where possible.
HCV genotyping should be undertaken if antiviral therapy is being considered.
Following an isolated acute percutaneous exposure to blood infected, or strongly suspected of being infected, with HCV, healthcare workers should be offered HCV RNA testing at 6, 12 and 24 weeks and anti-HCV testing at 12 and 24 weeks.
Good practice points
The testing procedure outlined in Figure 1 should be followed.
