Digital image of blood cells, including CD4 cells (yellow)

PLoS Medicine

[CAPE TOWN] A set of quick, cheap tests that analyse the health of HIV patients' immune systems has been unveiled.

The health of a person's immune system is usually used to guide whether they should start antiretroviral therapy. This is done by measuring the level of a certain type of immune cell — CD4 cells — in the blood. Once this is below 250 cells per microlitre, treatment starts.

But accessing CD4 testing is difficult in many developing countries because people often have to travel long distances to health centres with testing equipment. The equipment is also expensive to buy and run, requires specially trained operators and needs a good supply of electricity.

Steven Reid, a project manager in the division of medicine at the UK-based Imperial College London, told the 5th International AIDS Society (IAS) conference in Cape Town, South Africa, this week (21 July) that many patients in the developing world could gain access to CD4 testing for the first time with the new tests.

Reid's organisation, the CD4 Initiative, and partners have developed three prototype tests since beginning work in 2007. One is a fully quantitative test that 'counts' CD4 cells in blood samples by binding them with specific reagents and separating them into a fine tube — where the length of the resulting line of cells can be measured.

Reid said this quantitative test could also monitor how effective antiretroviral drugs are in both adults and children.

The others are simpler, using antibody-based colour changes to indicate whether the CD4 count is above or below 250 cells per microlitre or above 350 cells per microlitre.

The tests work with finger prick blood and have a simple readout, similar to a home pregnancy test. They should enable patients to receive their results within about 20 minutes of testing, Reid said, and can be used by untrained technicians.

"Healthcare workers rely on a CD4+ count to make decisions about how patients should be treated and when they should begin antiretroviral therapy," Reid told SciDev.Net.

The tests should be ready for shipping to developing nations by 2010 and in some countries the Bill and Melinda Gates Foundation, which funded their development, will form partnerships with governments to subsidise costs.

The quantitative device currently costs US$7, with the other tests costing US$2 and US$4. The CD4 Initiative partners are working to make them cheaper.