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SOUTH AFRICA: Rapid HIV tests not infallible

06 Oct 2008 16:38:22 GMT
Source: IRIN

Background

• Health and diseases

• AIDS in Africa

• AIDS pandemic

JOHANNESBURG, 6 October 2008 (IRIN) - The reliability of HIV diagnoses obtained from finger prick tests has come into question with the recall of a brand of rapid HIV test kits used at public testing sites in two South African provinces.

A local newspaper reported on 28 September that more than half a million Wondfo Rapid One Step Test kits, manufactured in China and supplied by FutureMed Pharmaceuticals, were withdrawn in late July after they were found to be defective.

The development of rapid HIV tests, which provide results in less than 30 minutes and can be carried out with minimal equipment or training, has greatly increased both the accessibility of testing and the numbers of people tested.

Miriam Mhazo, a senior programme manager at New Start, a non-profit organisation that provides voluntary HIV counselling and testing (VCT) services throughout the country, told IRIN/PlusNews that before her organisation starting using rapid tests in 2004, clients had to wait eight days to receive their results, and "about 30 percent wouldn't come back."

But several recent studies have uncovered problems with the performance of certain brands of rapid test kits, and with the level of user error in busy public health facilities where they are used.

User error

A study at 12 sites providing prevention of mother-to-child (PMTCT) services in KwaZulu-Natal Province evaluated HIV rapid tests performed on 961 women.

"There have been isolated reports of false positive results with rapid HIV tests in KwaZulu-Natal," said the study's lead investigator, Dhayendre Moodley of the Women's Health and HIV Research Unit at the University of KwaZulu-Natal.

"Surprisingly, most of these tests are FDA [US Food and Drug Administration] approved, as well as evaluated and approved by our National Laboratory Services, prior to their use in the public health sector. We therefore decided to determine if the error lies with the test or with the user."

Four different brands of rapid tests were evaluated and test results obtained by nurses and counsellors were compared to those obtained by laboratory technicians. Accuracy was determined according to whether two tests achieved the same result for the same individual - "concordance".

The study found that whereas the laboratory technicians using the rapid tests achieved 100 percent concordance, the nurses and counsellors achieved only between 92 and 98 percent.

Although some brands of test kits were slightly more sensitive than others, they all met World Health Organisation standards when performed in laboratories.

The investigators concluded that only user errors, such as applying an incorrect volume of the activating agent, could explain why the tests yielded less reliable results when performed by nurses and counsellors. Other problems could include incorrect interpretation of results or misidentification of specimens or tests.

"With any kind of laboratory test, one needs to follow the manufacturer's instructions to every detail," commented Moodley. "With these tests, the instructions are very clear and simple, and if people are trained and follow the method, there shouldn't be a problem."

In an article published in the September issue of the South African Medical Journal (SAMJ), Moodley and her colleagues recommended more ongoing training and supervision of health workers carrying out rapid HIV tests, and a system to ensure quality control.

She noted that although guidelines for regularly comparing rapid test results with the results obtained from more sophisticated laboratory tests were in place, they were not being implemented at all health facilities.

Devastating consequences

The consequences of receiving an incorrect HIV test result are potentially devastating. Someone who has received a false negative result could unknowingly infect others and also miss the opportunity of receiving treatment, while false positive results could sometimes lead to "severe physical trauma from partners, abandonment, and suicides", the SAMJ article said.

Moodley recalled some isolated cases where patients had participated in clinical trials because they had tested HIV-positive at public health facilities, only to discover they were negative when tested by laboratory tests.

Another recent study, also conducted in KwaZulu-Natal, tested four different types of rapid HIV test kits and found them to be less reliable than the manufacturers claimed: of the 751 patients who tested negative or had discordant results from rapid tests, 19 turned out to be HIV-positive.

The authors concluded that rapid HIV tests could lead to "substantial numbers of false negative results" in a high-prevalence setting like South Africa.

"We welcome the rapid test, knowing the laboratory constraints the country faces, and the benefits of getting results on the spot," Moodley said. "But I believe we need to be more selective in the types of rapid tests we use, and that selection should be based on prior field evaluation, in addition to laboratory evaluations."

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