Researchers have replicated the CD4+ T cell count test, which is normally conducted on an expensive flow cytometer machine using fresh blood, using dried blood and inexpensive commercially available reagents, a discovery that could simplify antiretroviral treatment monitoring for doctors in resource-poor settings, according to a study published in the Nov. 1 issue of the Lancet, Agence France-Presse reports. Standard flow cytometry tests, in which a $35,000 machine is used to count CD4+ cells as they pass through a laser, need to be staffed and maintained by trained personnel and require fresh blood samples, meaning that patients must be within two hours from a lab. Such requirements represent "crippling burdens" for developing countries, according to Agence France-Presse (Agence France-Presse, 10/31). A cheaper, more field-friendly test needs to be developed for resource-poor countries, where antiretroviral drugs will soon become widely available, the study authors say (Mwaba et al., Lancet, 11/1).
Alimuddin Zumla, a professor at the Centre for Infectious Diseases and International Health at University College London, and colleagues drew blood from 42 HIV-positive people in Zambia (Agence France-Presse, 10/31). The researchers dried the blood on filter paper and measured CD4+ cell levels using a commercial enzyme immunoassay, comparing the results to those obtained through standard flow cytometry tests of liquid blood samples. Results obtained through the filter paper technique "accorded well" with the results of the flow cytometry testing for patients with CD4+ counts greater than 200 cells/mm3. The mean CD4+ cell count result using the flow cytometry technique was 289 cells/mm3 and for the filter paper was 347 cells/mm3. However, the difference between the two methods rose significantly for CD4+ cell counts less than 200 cells/mm3 (Lancet, 11/1). CD4+ counts lower than 200 cells/mm3 of blood usually indicate a damaged immune system and indicate that a patient could be a candidate for antiretroviral drugs.
Although the test still has to be perfected, it could enable small local clinics to take blood samples of HIV-positive people, dry them on filter paper and mail them to labs for analysis, according to Zumla. The technique could reduce the cost of measuring CD4+ cell levels from between $20 and $40 per person to 50 cents per person, including the costs of lab technician salaries (Agence France-Presse, 10/31). Keith Alcorn of the British advocacy group National AIDS Manual said the research is "potentially interesting," but he added that patients in developing countries often do not seek medical assistance until their cell counts are much lower than 200 cells/mm3. "Until they can measure people with lower counts, [the filter paper technique] may have limited usefulness," Alcorn said, adding, "But if they can sort that out, so it is more reliable in people with more advanced disease, then it will represent a very important step, because blood won't have to be stored and it will be easier to transport ... to the lab" (BBC News, 10/31).
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