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Q. Is western blot test accurate and reliable to detect HIV?


Hello doctor,

My doctor has recommended western blot for HIV-1 and HIV-2 as a screening test. The RIBA test was negative for HIV, after 16 weeks of exposure. I also had a negative CMIA test, after 12 weeks post exposure. Hepatitis and STD panel are also negative. Is a negative western blot 100 % accurate and reliable at 16 weeks post-exposure? If western blot is so accurate, why it is not used as a screening test? Is a six months retest required despite a negative western blot at 16 weeks? Which generation is RIBA, and how accurate it is as a stand-alone screening test? Will a recent CMV affect these test results accuracy?

Related Questions:
Please explain about the CMIA test for HIV testing.
What is the frequency to do HIV testing while taking PEP?
Are my symptoms due to HIV infection? I had a high-risk exposure 15 months ago.

Dr. Ravinder Kaur Sachdeva
HIV/AIDS Specialist


Welcome to icliniq.com.

  • Western blot is highly sensitive and specific test, which is run after a repeatedly reactive ELISA or HIV (human immunodeficiency virus) rapid test. Western blot test is not used as a diagnostic test in the absence of an initial positive screening test, due to the rare possibility of false positive. It is a confirmatory test, and not meant as a primary test and carries value in confirming a positive rapid test or ELISA.
  • You can be 100 % certain if western blot has been performed at 16 weeks post-exposure and is giving a negative result, that you do not have HIV.
  • Rapid tests or ELISA (enzyme-linked immunosorbent assay) are almost always used as the first screening method. These are inexpensive and at the same time highly sensitive for detecting the presence of HIV antibodies. The rapid kits which are now available give an accurate result.
  • As per the testing guidelines, a repeat HIV testing should be provided to all individuals who have tested HIV negative, but where a possible exposure has occurred within the window period. Window period refers to the time after infection and before seroconversion, which means markers of infection (HIV-specific antigen and antibody) are still absent or too low to be detected by the test. There is natural variation in this period and is difficult to make for a particular person.
  • A negative test at 12 weeks definitely excludes HIV infection, had there been no other exposure. Your negative HIV test results are very encouraging, but if you had exposure, and as per the recommendations, I advise you to undertake HIV-antibody test at six months of exposure.
  • HIV proteins used in western blot can be produced by recombinant DNA (deoxyribonucleic acid) in a technique which is called RIBA (recombinant immunoblot assay). It is categorized as HIV third generation test.
  • Yes, a recent CMV (cytomegalovirus) infection and for that matter, any acute illness can interfere with the results.

Hope your queries are answered, but if you still have any more questions, please revert.

For further queries consult an HIV AIDS specialist online --> https://www.icliniq.com/ask-a-doctor-online/HIV-AIDS-specialist

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