Thousands of people wrongly believe they are HIV infected because of the standard Western blot test which is giving false positive results in nearly 5 per cent of cases.
This alarming inaccuracy has been uncovered by University of California researchers, who urge anyone who has been tested positive by a Western blot result to seek further advice, and possibly to be tested again. There is a better than 50 per cent chance that the test was a false positive if one of the three gene products tested known as p31, or polymerase protein was a negative.
The researchers have found that the p31 test in the Western blot procedure is very likely to throw up false positives. They tested the blood of five million donors and found that, of the 421 donors who were tested positive by Western blot, 39, or 9.3 per cent, of these were possibly false positives because they had not reacted to the p31 element of the test. Of these, 20, or 51.3 per cent, were proven by the PCR test not to be infected with HIV-1. This means that the Western blot test was giving a false reading in 4.8 per cent of all cases (JAMA, 1998; 280: 1080-85).