Several reliable, sensitive ELISA tests are approved for general use in Australia. A strongly positive ELISA test will rarely be falsely positive but weakly positive results may be difficult to interpret. Positive ELISA tests should be confirmed. A confirmed positive test for antibody indicates that the person has been infected by the virus.
There is good evidence that more than 96% of patients infected with HIV will develop antibodies detectable by an ELISA test. Antibody is detectable within 4 to 12 weeks of infection in most cases. For practical purposes all seropositive persons should be regarded as carriers.
Prior to the development of signs and symptoms, tests of immune function will usually be in normal limits. As immune deficiency develops, the characteristic change in immune function is a fall in T-helper cells. T-helper cells (with CD4 markers) can be distinguished from T-suppressor cells (carrying CD8 markers) using modem immunological techniques. Evidence of defective cell mediated immunity is defined as reduction of CD4+ cells to less than 0.4 x 109 per litre.
In an antibody positive patient, a fall in CD4+ cells is ominous and may herald the onset of Group IV disease. Other non-specific immunological abnormalities in these patients include hypergammaglobulinaemia and elevated B-2 microglobulin.
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