PCR Test Cautions

Issue #60 of AIDS Treatment News described the new PCR test, a very sensitive biochemical test for HIV. After reading the article, Joseph Sonnabend, M.D. called to alert us to the controversy over whether this research test is ready for clinical diagnostic use, because of the unknown risk that it could produce false positives or false negatives. Dr. Sonnabend and others, some speaking off the record, alerted us to the following information and concerns:
* The PCR test is so sensitive that sometimes it can detect a single molecule of the DNA being looked for. Therefore it is also extremely sensitive to even the tiniest contamination of laboratory glassware, reagents, etc.
* Even small variations in the chemicals used in the test can cause large differences in the result. And no one has yet made sure that the test works in a standard way when performed in different laboratories.
* Although about 200 people at least have already been tested with the PCR, this number is too small to provide very accurate data on the risk of false positives or false negatives.
* It is too early to be sure of the clinical meaning of a PCR test.
Most experts seem to agree (1) that the PCR should not be used by itself for diagnosing patients, and that (2) this very important research test may also be useful for diagnosis after more is known about it. Whether the PCR should be used at all at this time for diagnosing patients remains controversial.
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