IAS: $7 viral load test equivalent to more expensive high tech viral load tests, Malawi study shows

A test for HIV levels in the blood that can spot treatment failure using similar technology to HIV antibody testing yields results that are almost as accurate as the viral load tests now in use in the developed world, but at a fraction of the cost, researchers from Malawi and the University of North Carolina reported last month at the Third International AIDS Society Conference on HIV Pathogenesis and Treatment in Rio de Janeiro, Brazil.

The Exavir RT assay is manufactured by the Swedish diagnostics company Cavidi, and uses the ELISA technology employed in HIV antibody testing to detect HIV’s reverse transcriptase enzyme. In contrast, viral load tests manufactured by Roche, Abbott and Bayer employ techniques to directly capture and amplify HIV by using a technique called polymerase chain reaction, which requires sophisticated laboratory equipment and highly trained staff.

The RT assay is designed for use in resource-limited settings where it may be impossible to use PCR, but its perfomance in the field had not been evaluated previously. At last month’s conference, Mina Hosseinipour of the University of North Carolina reported on a comparison between the Exavir assay and the Roche Monitor 1.5 assay carried out in patients starting antiretroviral treatment at the Lighthouse Clinic in Lilongwe, Malawi.

Viral load was monitored every three months using the Roche Monitor 1.5, and a subset of samples from 102 patients at 152 time points were available for comparison using the ExaVIR assay (95 from baseline, the remainder from time points out to 12 months of treatment in fewer patients).

The samples showed a high level of agreement (correlation coefficent: 0.91), with 70% of samples that were undetectable (<400 copies/ml) by Roche Monitor assay also undetectable (<200 copies/ml) by Exavir assay or below 515 copies/ml. In general HIV RNA was higher for a given sample than HIV RT. The Exavir assay had a sensitivity of 71% and a specificity of 91%, and the investigators commented that “sensitivity at the lowest limit of detection is likely acceptable for clinical management.”

The cost of the test works out around $7 a test, compared to approximately $30 for an HIV RNA test, making the test somewhat more accessible.

However the authors also noted that the Cavidi assay may not be appropriate for rolling out to district hospitals. “While the cost of the Cavidi Exavir test is substantially less than HIV RNA and the test perfomance is comparable, it remains technically challenging, requires relatively large volumes of plasma for analysis and is time-consuming. The assay’s use in resource-poor settings as currently designed will likely be limited to centres of excellence or central hospital settings.”

The study was sponsored by the Doris Duke Charitable Foundation as a part of a programme of grants to promote research into low cost monitoring tools for HIV infection in resource-limited settings.