A cheaper and easier way to monitor HIV in patients could revolutionise global health care, according to scientists in the US.

The World Health Organization estimates that more than 33 million people worldwide have HIV. HIV destroys white blood cells called CD4+ T lymphocytes that are crucial for fighting disease. It also reduces the body's ability to replace these cells. Scientists use a technique called flow cytometry to monitor changes in patients' CD4+ levels - when they drop below 200 cells per microlitre, the patient is diagnosed with AIDS and prescribed anti-retroviral drugs. But flow cytometry requires expensive equipment and highly trained scientists to use it.

The microfluidic device separates the monocytes from blood and counts the lymphocytes with high selectivity and sensitivity

Mehmet Toner and colleagues at Massachusetts General Hospital, Boston, have modified a microfluidic device they were previously working on to overcome its major pitfall - sample contamination with another type of white blood cell called monocytes. They developed an upstream monocyte depletion module, which separates monocytes from blood samples before the lymphocytes are counted. Using the module, Toner measured the lymphocyte count with higher selectivity and sensitivity than before. Toner says the device has 'the potential to be one of the holy grails of global health'.

'The device assertively contributes to point of care testing from whole blood and may additionally facilitate other on-chip integrated whole blood-based assays,' says Philip Day, a expert in tool miniaturisation for quantitative molecular biology from the University of Manchester, UK.

Toner says his device is simpler and cheaper than flow cytometry, meaning it could be used in the resource-scarce settings of developing countries. The method, combined with the recent fall in HIV drug prices, should lead to significant progress in the fight against HIV, he adds.

Jennifer Newton

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