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Laboratory Diagnosis of HIV Infection

Indeterminate HIV-1 Antibody Western Blot Results

Slide 9

October 2009

There are some well-known causes of indeterminate HIV-1 antibody Western blot results. I’ve listed them here. Most frequently, we see are due to nonspecific reactions, so there are some proteins or antibodies in the patient serum, particularly those with autoimmune disorders such as SLE rheumatoid arthritis that can cross react with the antigen on the Western blot strips. Another major group that we’ve seen indeterminate Western blot in a false-positive screening antibody test is the pregnant women, because they produce allo-antibodies during pregnancy and these antibodies tend to cross-react with the HIV-1 and -2 antibody screening tests as well as the Western blot results.

So the approach with individuals with such indeterminate Western blot results is to repeat antibody testing in 2 to 4 weeks in high-risk individuals. For low-risk individuals, repeat testing is recommended in 3 to 6 months. In pregnant women, they are likely to have a false-positive antibody screening test and indeterminate Western blot results until 1 month after delivery, where the allo-antibodies are cleared from their system. The other possibility, instead of waiting 2 to 4 weeks in high-risk individuals, is to proceed to detection of HIV-1 RNA or proviral DNA using molecular tests.

Indeterminate HIV-1


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