0%-100% specificity of the PCR Test? 5 December 2003
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Christopher J Noble,
postdoctoral fellow

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Re: 0%-100% specificity of the PCR Test?

The Perth Group wrote:

"Would Christopher Noble also please explain the 0%-100% specificity of the PCR Test?"


In the meta-analysis study the authors "accepted positive results on conventional antibody tests (if they included a confirmatory Western Blot analysis or similar test) or viral cultures as high quality evidence of infection", that is, as a gold standard for PCR In search of 17 computer databases, they "identified 5698 titles of potential relevant articles. After independent review by two readers, 1735 titles were judged to be potentially relevant". Then they "reviewed the associated abstracts and then selected 379 studies published as full articles for further review. Of these 379 articles 96 met the inclusion criteria and were analysed". Unlike Christopher Noble who claims that "The metastudy however showed that PCR can be highly specific", the authors of the study reported: "When indeterminate PCR results were excluded, sensitivity ranged from 10% to 100% and specificity from 0% to 100%" and concluded "Our investigation produced two main findings. First, the false-positive and false-negative rates of PCR that we determined are too high to warrant a broader role for PCR in either routine screening or in the confirmation of diagnosis of HIV infection. This conclusion is true even for the results reported from more recent, high-quality studies that used commercially available, standardised PCR assays…We did not find evidence that the performance of PCR improved over time".11

I would like to ask the Perth Group why they have falsely quoted the meta-study by Owens et al. 1

The correct quote is "When indeterminate PCR results were excluded, sensitivity ranged from 10% to 100% and specificity ranged from 40% to 100%"

How can I explain something that is not true?

This misquote has now propagated over the internet. http://www.healtoronto.com/nih/main.html

How is it possible for the Perth Group to look at the same study and make such completely different conclusions? The study contradicts their assertions that PCR and antibody testing are both non-specific.

Why is it so necessary to read the actual study rather than to simply rely on their "interpretation"?

The Perth Group ask: "How is it possible for us to have such an influence with the President of South Africa and his Government when we have so little with the scientific community?"

We finally get back to the topic of this 'debate': The politics of AIDS in South Africa.

Thnakfully South Africa finally seems to be moving beyond the rhetoric and polemic that was provided by the "Perth Group" and other "Dissidents".

(1) Owens DK, Holodniy M, Garber AM, Scott J, Sonnad S, Moses L, et al. Polymerase chain reaction for the diagnosis of HIV infection in adults. A meta-analysis with recommendations for clinical practice and study design. Ann Int Med 1996;124(9):803-15

Competing interests: None declared