Burnet's low-cost Point-of-Care CD4 Test
It’s a cruel catch-22. Vastly improved antiviral drugs have the potential to significantly improve the lives of people with HIV. But before this can happen, they need to take a test. Trouble is, the test is slow and costly, so many miss out on treatment.
Now that could be about to change. Within 12 months, a new test could speed up this process and improve access to HIV treatment for millions around the world.
Of the 40 million HIV-infected individuals worldwide, around 35 million live in developing countries where health care resources are scarce.
HIV is most prevalent in the African continent, but no developing countries are spared from the epidemic. Some regions such as Eastern Europe are experiencing very rapid increases.
With no effective vaccines in sight, some five million new HIV infections occur worldwide each year.
Antiretroviral drug therapies offer the most hope for those infected with HIV, preventing the dramatic loss of immune function that signals advancement of the disease to AIDS, opportunistic infections and death.
The costs of high quality antiviral drugs are reducing and they are therefore increasingly available in developing countries.
Why, then, does UNAIDS (the Joint United Nations Programme on HIV/AIDS) currently estimate that around 15 million patients lack appropriate access to therapy?
The major problem is that appropriate use of antiretroviral therapies requires regular testing of each patient’s immune system, to determine when they should commence therapy.
This testing determines the number of a particular white cell in the blood, known as the CD4+ T-cell (“CD4 counts”).
The World Health Organization recommends that patients should commence therapy when CD4 counts fall below 350,000 per ml; normal healthy counts in adults exceed 500,000 per ml.
HIV-infected patients may remain at healthy CD4 counts for many years before they require drug therapy.
The current test
CD4 testing currently uses a process known as Flow Cytometry.
Flow Cytometry is a powerful technique in cutting-edge immunology research and clinical medicine, but the cost of each individual tests is significant (more than $10).
It also requires trained health workers to collect venous blood, and highly trained technicians to perform the tests on sophisticated equipment that is expensive and requires power, clean water and regular maintenance.
Results are usually not available until the following day, requiring follow-up of patients. Flow Cytometry therefore offers only a partial solution for developing countries.
These problems could largely be overcome by the use of suitable “Point of Care” (PoC) tests for CD4 T-cells.
PoC tests can typically be conducted in clinics or remote health facilities, giving immediate results without the use of equipment or highly trained workers.
PoC tests are already used throughout the developing world for diagnosis of HIV and other infectious diseases such as malaria and hepatitis B.
These tests look similar to home pregnancy tests, but use a drop of finger-prick blood rather than urine as the test sample.
The Burnet test
Over the past six years, Melbourne’s Burnet Institute has led the development of the first such PoC test for CD4+ T-cells.
The Burnet CD4 test uses a small volume of finger-prick blood, which is applied to the test device along with a drop of liquid (buffer) from a supplied dropper bottle.
From this drop of blood, the red blood cells and other contaminating cells are retained in the initial sample pad. White blood cells (including CD4+ T-cells) are diverted into a second region of the device containing detergent.
When the white blood cells interact with the detergent, their components flow along a membrane in the device, and the relevant CD4 protein is captured at a test line.
A further three drops of buffer are added to a second window of the device, generating a visible, coloured reaction at both the test line and a second reference line from which to compare the CD4 levels.
After a total test time of 40 minutes, the operator makes a visual comparison of the test line (CD4) and reference line (cutoff), and determines whether the CD4 count is above or below the recommended cutoff to commence therapy.
The Burnet PoC CD4 test has performed well in small-scale trials of HIV-infected patients in Australia and the USA, and larger-scale trials will commence throughout 2011, initially in patients in the USA and Africa.
There are still some significant hurdles to be passed before the test can be made widely available.
If the clinical trials are successful, the technology will be transferred to large-scale manufacturers to enable the production of the tests, at around $2 each.
If we’re successful the test will provide improved, cost-effective testing for 30 million patients worldwide.
For the 15 million patients who could then gain access to antiviral therapy, this will result in better health, along with better standards of living for their families, and reduced transmission of the virus.
David’s article is also available at The Conversation.