Diagnosis of Hepatitis C

Anna Lok, M.D.
Naresh T. Gunaratnam, M.D.

Diagnosis of Hepatitis C involves confirmation of the diagnosis of Hepatitis C virus (HCV) infection and assessment of the severity of liver disease. In addition, evaluation of patients with Hepatitis C should include determination of the patients’ suitability for treatment.

Currently, the second-generation enzyme immunoassay (EIA-2) for antibodies to HCV (anti-HCV) is the most practical screening test for HCV infection. The diagnosis of HCV infection can be supported or confirmed by the recombinant immunoblot assay (RIBA) or tests for HCV RNA. RIBA detects antibodies to individual HCV antigens and confers increased specificity compared to EIA-2. Qualitative reverse transcription- polymerase chain reaction (RT-PCR) assays for HCV RNA are simpler than quantitative tests and sufficient for confirmation of the diagnosis of HCV infection.

While the vast majority of anti-HCV- positive patients who present with chronic liver disease have ongoing HCV infection as confirmed by the presence of HCV RNA in serum, only 35 percent and 25 percent of anti-HCV-positive blood donors are RIBA- and HCV RNA-positive, respectively.

(1-5) The proportion of anti-HCV-positive blood donors who are confirmed to be HCV RNA-positive varies from 70 percent for those who are RIBA-positive to 2-25 percent for those who are RIBA- indeterminate and none for those who are RlBA-negative. Thus, supplementary and confirmatory tests for HCV infection should always be performed in asymptomatic low-risk subjects who are found to be anti-HCV-positive, particularly if they have normal aminotransferase (ALT) levels; but these tests may not be necessary in all anti-HCV-positive patients who present with chronic liver disease.

Severity of liver disease is best assessed by liver biopsy. There is in general a poor correlation between serum ALT level and activity of liver disease. More importantly, several recent studies found that significant liver disease can be found in anti-HCV-positive patients despite normal ALT levels. (1-3,5-8) These studies reported that 70 percent of RIBA- positive blood donors who had persistently normal ALT levels have chronic hepatitis or cirrhosis on biopsy. Although most donors (77 percent) who had abnormal liver histology were HCV RNA-positive, significant liver disease was also found in 30 percent of RlBA- positive donors who were HCV RNA- negative and had normal ALT levels on three separate occasions. This may be related to the fluctuating course of chronic HCV infection with intermittently normal ALT levels and undetectable levels of viremia. It may also reflect variations in sensitivities of “home-made” RT-PCR assays for HCV RNA. (9) Several studies reported that patients with more advanced liver disease had higher serum HCV RNA levels. (10-13) However, these findings were not confirmed by other studies. (14,15) It is unlikely that quantitative tests for HCV RNA will replace liver biopsy in the determination of activity or stage of liver disease. HCV genotype I b has been shown to be associated with more advanced liver disease. (16-18) Nevertheless, there is a wide spread in severity of liver disease associated with each genotype. Thus, genotyping cannot be used to determine severity of liver disease.

The most important factors associated with favorable response to interferon therapy are low pretreatment serum HCV RNA level, HCV genotypes 2 and 3, and absence of cirrhosis or significant fibrosis. (19-24) More recently, some studies have also reported that responders have a more rapid fall in serum HCV RNA level during the first few weeks of treatment. (25,26) The predictive factors of response will be discussed in more detail by Dr. Davis. Qualitative tests for HCV RNA are increasingly used to assess virological response during treatment. However, it is uncertain whether certain test results of diagnostic evaluation should be used to exclude patients who have low probability of response from receiving treatment.

In summary, the diagnostic algorithm of Hepatitis C depends on the clinical context. In asymptomatic, low-risk subjects, who are found to be anti-HCV- positive by EIA-2, the diagnosis of HCV infection needs to be confirmed, especially if the initial biochemical tests reveal normal ALT levels.

This may be achieved by retesting for anti HCV by RIBA. Those who are RlBA- positive or indeterminate will then be tested for HCV RNA using qualitative RT- PCR assays. It can be argued that confirmation of the diagnosis of HCV infection can be accomplished in a single step by testing for HCV RNA directly, since this test will eventually be performed on 70 percent of these subjects. Nevertheless, 30 percent of RlBA-positive blood donors are HCV RNA negative when tested on a single occasion, (1,3,4) and significant liver disease had been detected in 30 percent of RIBA-positive blood donors who are HCV RNA- negative. (1) In addition, new versions of RIBA may reduce the proportion of those with indeterminate results, thus decreasing the need for HCV RNA testing. In view of the fluctuating nature of chronic HCV infection, repeat tests for ALT levels are needed to differentiate subjects with persistently normal ALT levels from those with intermittently elevated ALT levels, since the prognosis and plan of treatment may be different in these two groups of patients. Several studies reported that the proportion of anti-HCV blood donors with elevated ALT levels increased by 10 percent to 20 percent during a 6-month followup period. (5,6) While it is clear that liver biopsy is the most reliable way to assess the activity and stage of liver disease and should be recommended in anti-HCV-positive subjects who are HCV RNA-positive and have elevated ALT levels, it is less clear whether liver biopsy should be routinely recommended in those who are HCV RNA-positive and have persistently normal ALT levels, until the natural history of this subset of patients is better defined and when an effective treatment becomes available.

The vast majority of patients who present with chronic liver disease and are found to be anti-HCVpositive by EIA-2 have HCV infection, especially if risk factors are present.

Confirmatory tests may not be necessary in all patients. When performed, tests for HCV RNA are more appropriate than RIBA. While qualitative test for HCV RNA will suffice to confirm the diagnosis, quantitative RT-PCR or branched DNA assay to determine HCV RNA level may be performed if treatment is contemplated. Liver biopsy should be recommended except in elderly patients, patients with severe concomitant medical problems, and those with coagulopathy, since neither serum HCV RNA nor ALT level can reliably predict activity or degree of fibrosis.

At the moment, HCV genotyping should be considered a research tool and not a part of the diagnostic algorithm in clinical practice.