Chronic Hepatitis C: Current Disease Management

Enzyme Immunoassay

Anti-HCV is detected by enzyme immunoassay (EIA). The third-generation test (EIA-3) used today is more sensitive and specific than previous tests. However, as with all enzyme immunoassays, false positive results are a problem with the EIA-3. False positive reactions are particularly common among patients with rheumatoid factor or high levels of immunoglobulins, and when stored serum samples are tested. Therefore, in most situations a positive EIA test should be confirmed by using another method such as recombinant immunoblot assay (RIBA) or polymerase chain reaction (PCR) amplification for HCV RNA.

Other problems with EIA tests are that immunocompromised patients may not produce enough antibodies for detection with EIA and patients with acute hepatitis may test negative for anti-HCV when they first present to the physician. Antibody is present in almost all patients by 1 month after onset of acute illness; thus patients with acute hepatitis who initially test negative may need followup testing.

Recombinant Immunoblot Assay

Immunoblot assays are used to confirm anti-HCV reactivity. These tests are also called "Western blots"; serum is incubated on nitrocellulose strips on which four recombinant viral proteins are blotted. Color changes indicate that antibodies are adhering to the proteins. An immunoblot is considered positive if more than one protein reacts and considered indeterminate if only one positive band is detected. Early in the course of acute hepatitis C, patients often have an indeterminate immunoblot, developing antibody reactivity to the other proteins with time. This test is routinely done in blood banks when an anti-HCV positive sample is found by EIA. Immunoblot assays are highly specific and valuable in verifying anti-HCV reactivity. Indeterminate tests require further followup testing, including attempts to confirm the specificity by testing for HCV RNA.

PCR Amplification

PCR amplification can detect low levels of HCV RNA in serum. Testing for HCV RNA is a reliable way of demonstrating that hepatitis C infection is present and is the most specific test for infection. Testing for HCV RNA by PCR is particularly useful when aminotransferases are normal or only slightly elevated, when anti-HCV is not present, or when several causes of liver disease are possible. This method also helps in diagnosing hepatitis C in people who are immunosuppressed, have recently had an organ transplant, or have chronic renal failure. At present, however, there are no FDA-approved PCR assays for general use, although commercial test systems are available. Many commercial laboratories offer their own PCR assays, which are not subject to strict independent quality controls. Thus, the reliability and specificity of the PCR technique is not standardized. In addition, the PCR technique is expensive and prone to technical or laboratory error. When ordering HCV RNA testing by PCR, it is important that the physician use an excellent laboratory that is willing to document standardization of the test.

Quantification of HCV RNA in Serum

Several methods are available for measuring the titer or level of virus in serum, which is an indirect assessment of viral load. These methods include a quantitative PCR and a branched DNA (bDNA) test. Both assays are reasonably accurate, but there may be spontaneous variation in levels by 3- to 5-fold over time. These assays have been helpful in elucidating the nature of hepatitis C, but they are not generally clinically helpful. Thus, in HCV infection, viral load does not correlate with severity of illness or poor prognosis (as it seems to in HIV infection). When attempting to assess whether hepatitis C is present, these tests should not be ordered; instead, the more sensitive and reliable qualitative PCR for HCV RNA is needed.

Genotyping and Serotyping of HCV

There are six known genotypes and more than 30 subtypes of hepatitis C. The genotype of infection is helpful in defining the epidemiology of hepatitis C. The only clinical usefulness of knowing the genotype or serotype (genotype-specific antibodies) relates to interferon therapy. Patients with genotypes 2 and 3 are two to three times more likely to respond to alpha interferon therapy. However, the genotype of infection should not determine whether alpha interferon therapy is offered, as it is an imperfect predictor of response.

Normal Serum ALT Levels

Some patients with chronic hepatitis C have normal serum alanine aminotransferase (ALT) levels, even when tested on multiple occasions. In this and other situations in which the diagnosis of chronic hepatitis C may be questioned, the presence of anti-HCV alone should be confirmed by a supplemental test such as an immunoblot assay. Testing for HCV RNA may be helpful to confirm the presence of viremia.

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