Hepatitis Diagnostic Testing

Hepatitis C Antibody Testing

Two primary forms of testing are available for the detection of the anti-hepatitis C antibody (anti-HCV Ab): enzyme immunoassays (EIA) and recombinant immuno blot assays (RIE3A). These antibody tests are useful screening tools for hepatitis C, but they do have limitations.

Both of these antibody tests will yield a positive result for current (active) and resolved disease. Antibody testing may not become positive for 3-6 months after exposure, resulting in a delay diagnosis in the acute disease. Immuno suppressed patients such as those with renal failure, those infected with HIV, or those post-organ transplantation – may not express the hepatitis C antibody yet still may have hepatitis C infection. False-positive antibody testing may occur in low-risk blood donors. EIA Three generations of EIA antibody testing have been developed since 1989. The EIA antibody is the main screening test for hepatitis C. The first-generation EIA antibody, which incorporated the c100-3 epitope from the nonstructural NS4 region, was used until 1992, at which time it was replaced by a second-generation EIA. EIA-2 contains hepatitis C antigens from the viral core and from areas of the nonstructural NS3 and NS4 regions.162 A third-generation EIA that contains reconfigured core and NS3 antigens and a newly incorporated antigen from the NS5 region was recently approved by the United States Food and Drug Administration (FDA) for screening blood products and is now in use at some institutions for diagnostic purposes. EIA-3, with a sensitivity of 97%, offers slightly improved sensitivity over the 95% sensitivity seen with ElA-2. Most centers in the United States use EIA-2 testing.

EIA testing offers several distinct advantages in the diagnostic setting because these assays are easy to perform, are relatively inexpensive, and have high sensitivity. A positive EIA-antibody test requires a second confirmatory assay to make the diagnosis of hepatitis C. False-positive EIA testing may occur in low-risk patients and in patients with underlying autoimmune diseases. These patients may benefit from RIBA assay testing to differentiate a false-positive from a true-positive test.

RIBA: These tests are supplemental assays to EIA testing. Both classes of antibody assays contain the same HCV antigens. RIBA testing is currently in its third generation of development. RIBA-2 uses the same recombinant antigens as EIA-2.

Results from a RIBA-2 assay may be interpreted as positive if 2 or more antigens are positive, interpreted as indeterminate if 1 antigen is positive, or finally, interpreted as negative if all antigens are negative. RIBA testing is not more sensitive than EIA testing, but a RIBA-2 test can be used to distinguish between a false-positive EIA test and true previous exposure to hepatitis C. A third-generation RIBA test (RIBA-3) has recently been licensed in the United States. This assay incorporates the NS5 antigen with the standard antigens used in RIBA-2. This third-generation test produces a reduced number of indeterminate results and is more specific than the RIBA-2 assay.

ROLE OF OTHER FACTORS:

Many factors initially considered to be important predictors of disease progression appear, in fact, not to have such a predictive role. These factors include mode of transmission, serum transaminase levels, hepatitis C viral loads, and hepatitis C genotype. The authors of one paper, however, concluded that transfusion- acquired disease was associated with more rapid disease progression than was disease acquisition due to other risk factors.

CLINICAL PRESENTATION

Most patients with hepatitis C are asymptomatic. But if symptoms do occur, the most common complaints are fatigue, abdominal pain, poor appetite, weight loss, and pruntus. The diagnosis of hepatitis C is made following the completion of specific tests requested by the clinician. The primary care physician generally performs this testing if risk factors are identified or abnormal liver chemistries noted. Blood banks and life insurance companies routinely test blood donors and applicants for hepatitis C. Hepatitis C testing, unlike testing for HIV, does not require that consent be obtained.

Hepatitis C can lead to a broad spectrum of liver disease. Patients may develop mild disease as evidenced by mild inflammation and/or fibrosis. Others may develop increasing amounts of inflammation or fibrosis, which can lead to the development of significant fibrosis or cirrhosis.

EXTRAHEPATIC MANIFESTATIONS
In addition to liver disease, hepatitis C is associated with a number of extra hepatic effects, including hematologic, renal, dermatologic, endocrine, and autoimmune disorders.

HEMATOLOGIC DISORDERS

Essential mixed cryoglobulinemia. Essential mixed cryoglobulinemia (EMC) is a condition that results in the deposition of circulating immune complexes in small- to medium-sized blood vessels. Patients with EMC usually present with rash, arthralgias, and weakness.

A review of the literature reveals that hepatitis C can be found in 95% of all patients with EMC. Several investigators have suggested that hepatitis C may have a causative role in EMC. Anti-HCV antibodies can be detected in the vessel walls of skin biopsies taken from patients with EMC and chronic vasculitis. Interferon therapy has been shown to reduce the cryocrit and allow symptomatic improvement of both rash and joint pains. The response is short-lived, however, because symptoms almost universally reappear upon cessation of therapy.

Lymphoma.
Several reports have described an increased incidence of B-cell lymphoma in patients with hepatitis C. Rasul and colleagues studied 16 patients with chronic hepatitis C and cryoglobutinemia for the presence of lymphoma. Results of bone marrow biopsy were consistent with non-Hodgkin’s lymphoma in 2 patients and suspicious for lymphoma in 7. While this finding needs to be evaluated further in larger studies, the development of lymphadenopathy or unexplained chronic anemia in a patient with hepatitis C infection should raise concern about the possibility of underlying lymphoma.

Renal Disorders
Glonierulonephritis has been associated with hepatitis C. These patients are found to have proteinuria, which can be significant and in the nephrotic range. Most cases of glomerulonephritis are associated with cryoglobulinemia. The most common histologic lesion seen is membranoproliferative glomerulonephritis. Interferon therapy may reduce proteinuria, but a sustained response is seldom achieved in these patients. Ribavirin should be avoided in patients with significant renal impairment. Some may benefit from the use of plasmapheresis, although the relief tends to be short-lived.

DERMATOLOGIC DISORDERS

Several dermatologic disorders have been described in association with hepatitis C. These include porphyria cutanea tarda, lichen planus, and cutaneous necrotizing vasculitis.

Porphyria cutanea tarda:
Porphyria cutanea tarda (PCT) is the most common form of porphyria. PCT ha been associated with hepatitis C infection, particularly in those patients with significant alcohol use. Hepatitis C may occur in 58% to 71% of all PCT patients. This dermatologic disorder tends to present at an earlier age in patients with hepatitis C than in those PCT patients without hepatitis C. Despite this association, the clinical changes seen in the setting of PCT do not appear to be a direct consequence of the viral infection.

Lichen planus:
This condition has been associated with hepatitis C, although hepatitis C has not been shown to be the causative agent.

Cutaneous necrotizing vasculitis: This condition has been associated With hepatitis C as well, although hepatitis C has not been shown to be the causative agent.

Endocrine Disorders:
Hepatitis C has also been linked to both diabetes mellitus and an increased incidence of anti-thyroid antibodies.

Diabetes mellitus:
An association between hepatitis C and diabetes mellitus has recently been demonstrated Mason and colleagues retrospectively evaluated patients with chronic hepatitis C and found this infection to be an independent predictor of diabetes.

Additionally, Mehta and associateS58l found that among individuals older than 40 years of age, those with hepatitis C infection were more than 3 times as likely to have type 2 diabetes mellitus than those without hepatitis C infection. The prevalence of type 1 diabetes was not increased. The link between these 2 disorders must be further investigated in an effort to improve available therapies.

Other Extra Hepatic Manifestations
Finally, hepatitis C has been associated with a number of other extrahepatic disorders as well, incluaing sialadenitis, uveitis, corneal ulceration, polyarteritis flodosa, peripheral neuropathy, and the development of autoimmune phenomena.