Specificity of HIV testing

Q: My Grandma, a rheumatoid arthritis patient, had a blood transfusion for a surgery 4 months ago. Two weeks ago, her HIV ELISA test was found to be positive. We then performed an HIV PCR test that was found to be negative. I would like to know the specificity of the test and whether an additional western blot test is necessary?

A: The decision to retest for HIV can be influenced by a couple different factors. First, we would like to emphasize that the risk of contracting HIV through a blood transfusion has been greatly reduced since the implementation of blood screening technology. According to the Red Cross, the chances of becoming infected through a blood transfusion is approximately 1 in 1.5 million units of blood.
Secondly, has a Western Blot already been performed? If so, when was it done and what was the result?
You also mentioned an HIV PCR test, and it is a great sign that the test came back negative. Do you know which PCR your grandmother had (HIV DNA PCR or HIV RNA PCR)?
If you can provide this information we may be able to offer some guidance in this difficult situation. Please feel free to email a response, and please include this post’s title in the subject line.