HIV Testing

Jean Michel Gershy-Damet of AFRO discussed the issues that must be considered when choosing diagnostic HIV tests in the context of VCT for pregnant women:

· operational factors such as: available laboratory infrastructure, available equipment to perform tests; technical skills of staff; number of tests to be performed; and cost.

· sensitivity and specificity of tests

· prevalence of HIV infection in the population: WHO advises to use strategy II (see below) for diagnosis of HIV in asymptomatic clients in populations with a prevalence of 10% or more, and strategy III if the prevalence is below 10%. In strategy II, all serum is first tested with one ELISA or simple/rapid assay, and any reactive samples are retested using a different assay. Serum that is not reactive in the first test is considered HIV antibody negative. Serum that is reactive in the first but not in the second assay should be tested again with both tests. In strategy III, a third test is required if serum is reactive on the second assay or on the repeated first assay. The tests used in strategy II or III should be based on different antigen preparations and/or different test principles.

The following table compares logistical considerations of ELISA and rapid/simple tests:

Quality assurance should include monitoring the performance of the test as well as the performance of the operator who carries out the test. Internal quality controls need to be included daily or with each run of the test. Results of a proportion of specimens should be checked in another laboratory. However, many problems are not due to the manufacturer: staff must follow standard operating procedures; equipment has to be maintained and calibrated; and supplies and equipment must be correctly stored. Measures are needed to avoid clerical or transcription errors.