Researchers have developed a new small, portable testing device that employs technology termed microfluidics as a way to quickly detect infectious diseases at the time that the patient is seen by the healthcare provider. In small initial studies, researchers evaluated its performance in Rwanda, Africa with promising results. A technical report describing the device and detailing results of the evaluations was published in the July issue of Nature Medicine.
Dubbed "mChip" for "mobile microfluidics chip for immunoassay on protein markers," the testing device was created to provide a reliable, inexpensive and easy-to-use test to identify individuals infected with certain diseases in areas with limited resources. The test detects antibodies produced in response to an infection. It is intended to be used to screen people at the point of care, where they can receive treatment without delay if the result is positive. In addition to aiding those who are sick, early treatment helps to curb the spread of infections.
In developing the mChip, researchers sought to improve upon existing rapid point-of-care tests (POCTs). Current tests typically use one of a few simple methods similar to those employed by home pregnancy tests. The sample and reagent(s) are mixed or applied to a pad and a visible reaction occurs such as color change or appearance of a line to indicate a positive result. The mChip is similar to these rapid POCTs in having several advantages over laboratory-based assays: it requires only a small amount of sample, involves fewer steps, does not take extensive training to perform reliably, and produces results in about 20 minutes.
The new technology is distinct, however, in that it uses micro-channels through which the sample and reagents continuously flow. Reactions that indicate positive or negative results take place in "detection zones" within the channels. Some current POCTs require subjective interpretation of color development to determine if a test is positive or negative. In contrast, the mChip uses a reading device, no bigger than a cell phone, that objectively detects and interprets results. In this way, the mChip endeavors to improve upon the performance of current POCTs by using some of the same technology found in instruments used in laboratories but on a much smaller scale.
Another distinction is that the mChip allows testing for more than one disease at the same time, something that has been problematic for other POCTs. For the first version of the test, the developers chose to create one that simultaneously detects HIV and syphilis. The researchers intend for it to be used eventually to screen pregnant women because these are two diseases for which early treatment can decrease risk of transmission to the baby.
To assess performance of the technology in the field, the researchers first evaluated it at a hospital in Kigali, Rwanda that lacks sophisticated testing equipment. They used the mChip HIV test on 70 samples from individuals with known HIV status. They found only one discordant result that did not agree with the laboratory-based reference test. When an additional 101 samples that were previously tested in the laboratory were then tested for HIV using the mChip, similar sensitivity and specificity characteristics were observed as in the first trial with 70 samples.
Researchers then sought to determine the performance characteristics when the test is used to simultaneously detect HIV and syphilis. They tested 67 samples collected at a clinic using the combined test and compared results with those from laboratory-based reference tests. For HIV, there were three samples that tested falsely positive and none that tested falsely negative. The performance for syphilis was less sensitive and specific: three samples tested falsely negative and four tested falsely positive.
As with other screening tests, positive results from the mChip would require confirmation by a second, different test. While the outcomes of the evaluations in Rwanda are favorable, they were done on relatively small numbers of samples. Larger trials, encompassing a greater number of specimens, would further prove that the technology can perform consistently in the field. If deemed to be reliable, use of the technology could be expanded to include other infectious diseases, such as chlamydia and gonorrhea.
Though not designed to be used in developed nations, the researchers note that there could be applications for the mChip in doctor's offices or clinics that serve rural areas or regions that lack resources. However, this would require additional evaluations of the test to gain regulatory approval.
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Chin C, et al. Microfluidics-based diagnostics of infectious diseases in the developing world. Nature Medicine 17, 1015–1019 (2011). Supplemental information available online at http://www.nature.com/nm/journal/v17/n8/extref/nm.2408-S1.pdf through http://www.nature.com. Accessed Sept. 2, 2011.
Christian Torres (July 31, 2011). Rapid, cheap HIV test finds success as first of its kind tested in the field. Washington Post. Available online at http://www.washingtonpost.com/national/health-science/rapid-cheap-hiv-test-finds-success-as-first-of-its-kind-tested-in-the-field/2011/07/27/gIQAUo1dlI_story.html through http://www.washingtonpost.com. Accessed Sept. 2, 2011.
Branson B. Point-of-Care Rapid Tests for HIV Antibodies. J Lab Med 2003; 27 (7/8): 288-295. Available online at http://www.cdc.gov/hiv/topics/testing/resources/journal_article/J_Lab_Med_20031.htm through http://www.cdc.gov. Accessed Sept. 2, 2011.