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On-the-spot HIV diagnosis

03 Mar, 2014

US researchers have developed a handheld, battery-powered device that uses a single drop of blood to provide an accurate cell count in just a few minutes

Approximately 35 million people worldwide are infected with HIV, with much of this disease burden in remote or resource-limited areas. Researchers at the University of Illinois in the US have developed a microfluidic biochip the size of a large postage stamp for on-the-spot HIV/AIDS diagnosis using just a single drop of blood. The chip will allow patients in these remote or resource-poor places to be tested more easily.

Although at the prototype stage, the disposable chip is designed to eventually operate in a handheld, battery-powered device “that would deliver simple HIV diagnostics to patients anywhere in the world, regardless of geography or socioeconomic status,” including giving a count of an individual patient’s white blood cells, such as CD4+ and CD8+ T cells, to guide treatment, write the researchers.

CD4+ T cells are immune cells that are destroyed by HIV – a reduced number indicates the onset of HIV. As more T cells are destroyed, the patient’s disease progresses into AIDS (acquired immunodeficiency syndrome). A diagnosis of AIDS is made when CD4+ T cells fall below 200 cells per microlitre (μl) of whole blood.

Cheaper, faster results

According to the research paper, accurate cell counts can be provided in less than 20 minutes from one drop of whole blood. At present, HIV patients have to rely on a laboratory test using laser-based flow cytometry that requires a larger blood sample (which must be prepared in solution), expensive equipment and trained technicians. It is also time consuming, as the blood sample or the patient need to be sent to a lab.

After the patient has put a drop of blood onto the biochip (in the same way a person might put a spot of blood on a strip for a blood sugar test), the device works by passing the sample through five on-chip modules that perform various functions. Ultimately, an electrical current is run through the sample. Cells in the sample block the current, allowing their size, shape, type and ratio to be identified.

The chip was tested on the blood of healthy and HIV-infected participants and the results compared with control results obtained using flow cytometry. The results very closely matched over a range from 40 to 1000 cells/μl for CD4+ and CD8+ T cell counts.

Potential for use beyond HIV diagnosis

Insurance companies and immigration services might also be interested in the benefits of an easy HIV/AIDS diagnosis, as having the virus can be a restricting factor for life insurance or travel to other countries. The biochip could also be used for other diseases where white blood cell counts are needed, such as leukaemia, inflammatory diseases (such as rheumatoid arthritis) and liver disease.

According to the researchers, once the chips are mass produced, a test should cost less than US$10. The researchers have formed a spin-off company, Daktari Diagnostics, which will commercialise the chip.

The research and development of the device was published in the December 2013 issue of Science Translational Medicine.

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