Antibody assays
 

Rajender Reddy MD: Antibody assays in the right setting are quite reliable in the diagnosis of hepatitis C infection. There is an EIA assay and there is also a RIBA assay, which stands for "recombinant immunoblot assay."

EIA is the first assay that is done either in clinical practice or by the blood banks. This is a third-generation assay and in the right individual who has risk factors for hepatitis C infection or has an abnormal ALT, the presence of an EIA positive anti-HCV often indicates hepatitis C infection.

David Bernstein MD: It's a simple, inexpensive antibody test that is used to determine whether someone has either been exposed to the disease or has the disease. But it's just that and it needs some confirmation if you're going to decide that the patient actually has the disease.

In general, EIA tests become positive approximately four to twelve weeks after exposure to the hepatitis C virus. That's important, because if you're tracking someone with acute infection, antibody testing isn't the best way of finding that out.

The sensitivity and specificity of EIA have gotten much better. And at this stage, 80 to 90% sensitivity and specificity.

There are some patients that are going to have false negative results. In general, those are patients that have chronic renal failure on dialysis or those that may have severely altered immune states, and that can be patients who are HIV-infected or even those with, for example, severe diabetes that may be immunosuppressed.

The EIA test used in the evaluation of patients with hepatitis C can have some false positives. Those false positives are in patients that have other autoimmune diseases. Those autoimmune diseases include lupus, rheumatoid arthritis, diabetes, even thyroid disease.

Patients who have autoimmune disease who have positive EIA tests should have confirmatory testing to determine if they truly have hepatitis C. That confirmatory testing would be qualitative HCV-RNA testing.

Recombinant immunoblot assays are an antibody test that have been used in the past for evaluation of hepatitis C. As of the latest NIH consensus conference in June of 2002, they really have no role in the clinical, medical evaluation of someone who has hepatitis C. They're helpful in one particular situation.

Rajender Reddy MD: If you had a patient who was EIA positive but had no risk factors for hepatitis C infection and had a normal ALT, we could use the RIBA assay to see if this EIA anti-HCV is a true positive or a false positive. If RIBA is reactive then, it very likely indicates that the EIA was a true positive.