HIV test:Too inaccurate for comfort

The HIV test for detecting AIDS is surrounded by controversy. Leaving aside the arguments about the supposed link between HIV and AIDS – still hotly debated in medical circles – the test itself is inaccurate and inconsistent.

The basic test for HIV is the ELISA (enzyme-linked immunosorbent assay), a blood test designed to detect antibody responses to the human immunodeficiency virus. But no test is yet able to detect HIV itself, so antibody activity that suggests its presence is what’s looked for.

If this initial test is positive, the Western blot test is done to confirm the finding. Although this is considered a more accurate test, neither it nor the ELISA has a true ‘gold standard’, simply because the HIV has never been isolated.

Three scientists, including Eleni Papadopulos-Eleopulos, an arch critic of the HIV/AIDS link, have scrutinised both tests, and concluded that neither is standardised, which means that laboratories may interpret the results differently. The test is also not reproducible, and cross-reacts with other, non-HIV, proteins (BioTech, 1993; 6: 696-7).

The ELISA test was developed in 1985. It is extremely haphazard, and often gives a false-positive result – detecting HIV where none is present. As many as four out of five positive ELISAs cannot be confirmed by Western blotting, which gives an indication of the level of inaccuracy.

This inaccuracy was confirmed by the Papadopulos-Eleopulos study, which revealed that, in a testing programme using the US military, 4000 people had positive ELISA tests twice that were not confirmed by Western blot testing.

Perhaps the problem is because ELISA searches for a protein known as p24, which is generally accepted as proof of HIV. But even Dr Robert Gallo, the co-discoverer of the virus, accepts that p24 is not unique to HIV, but can also be found in people who suffer from hepatitis B and C, malaria, papillomavirus warts, glandular fever, tuberculosis, syphilis and leprosy (Nature, 1985; 317: 395-403). Equally, p24 is not found in all patients who have full-blown AIDS.

In one study, antibodies to p24 were detected in one out of 150 healthy individuals, 13 per cent of randomly selected patients with generalised papillomavirus warts, 24 per cent of those with cutaneous T-cell lymphoma and 41 per cent of people with multiple sclerosis (N Engl J Med, 1988; 318: 448-9).

Although believed to be far more reliable, the Western blot test is also unreliable. In one study of Venezuelan malaria patients, the rate of false positives with Western blot ranged from 25 to 41 per cent. The researchers concluded: ‘HIV is not causing AIDS, even in the presence of . . . acute malaria’ (N Engl J Med, 1986; 314: 647).

Attempts to develop more accurate tests have so far failed. A saliva test kit for HIV antibodies was tried on patients with HIV-1 but, in some cases, the kits were able to detect the virus in only 67 per cent of cases (Afr J Med Sci, 2001; 30: 305-8).