CORVALLIS, OREGON – In developed countries, most people take for granted that when they are sick, they will have access to timely diagnosis and treatment. Indeed, while the diagnostic process – which typically involves sending a sample of blood, urine, or tissue to a laboratory for analysis – may be cumbersome and expensive, health-care providers and sophisticated laboratories remain widely available. As a result, the disease burden in the developed world has declined substantially.
By contrast, in the developing world, millions of people die each year from treatable diseases like malaria, owing to the lack of sophisticated laboratories and alternative diagnostic tests. But there is reason for hope: Advances in the field of microfluidics have the potential to transform health care by allowing “gold standard” laboratory-based testing to be transferred to the point of care (POC).
A POC test that provides an accurate and timely result would provide diagnostic access to underserved populations, enabling earlier treatment and helping to avoid mistreatment (treating another disease with similar symptoms). In order to meet their potential, however, POC tests must account for the wide range of factors affecting health-care applications.
First, a POC test must meet the particular environmental and operating constraints of where it will be used. These may include an unreliable power supply, harsh or unpredictable environmental conditions, limited contact time between the health-care provider and patient, lack of user training, severe price constraints, and inadequate local infrastructure, which can impede the maintenance and repair of relevant instruments.
Indeed, POC settings can vary from a semi-trained health-care provider working in a clinic with electricity and access to refrigeration to an untrained individual in an environment with no mechanism for controlling temperature or humidity. In order to ensure the broadest coverage possible, POC tests should be designed to work in the settings with the fewest resources.
Likewise, POC tests must account for different tests’ requirements for clinical utility. While diagnosing malaria requires only a positive or negative result, an HIV viral-load test would need to provide a graded output indicating the amount of virus detected.
One of the most successful POC test formats is that of the well-known pregnancy test, which requires only the user’s urine and takes roughly 15 minutes to deliver the result. This class of “rapid diagnostic tests” (RDTs), which are also used for infectious diseases like malaria and HIV, satisfy many of the key requirements for global health applications: they are fast and inexpensive, can be conducted easily by an untrained user, and do not require refrigeration. But they lack the sensitivity to provide adequate diagnostic information for many health conditions.
Given this, researchers are working to develop more sophisticated paper-based tests. For example, a new class of device, about the size of a postage stamp, that splits a sample into multiple zones with different detection chemistries has been used to test multiple conditions associated with liver failure in HIV and tuberculosis patients. And “paper network” devices include built-in timing mechanisms to enable automated multi-step tests like those used in laboratories, but in a disposable format.
Another mechanism for expanding the capabilities of diagnostic testing would take advantage of the penetration of mobile-phone networks in developing countries. RDTs are largely limited to applications that require visual interpretation. A non-dedicated mobile phone could be used to capture and send image data from an RDT to a remote site, where a health-care provider would provide feedback on the results.
But implementing such a program raises a new set of challenges. In order to ensure accurate test results, the variability of camera positioning by the user and lighting conditions in different test environments must be addressed. (One promising approach under development would use an adapter to connect the non-dedicated mobile phone to the RDT.)
Moreover, a phone-based test would require software infrastructure, such as communication protocols and prioritization procedures, to coalesce with the health-care system. And the compatibility issues raised by the wide variety of mobile-phone handsets would need to be addressed.
Finally, the successful deployment of non-dedicated phone-based testing would require acceptance from the medical establishment. The US Food and Drug Administration’s recent approval of several medical devices supported by dedicated phone-based readers is a promising step.
Effective POC tests are being developed; the proliferation of mobile phones will further augment the capabilities of these tests. These emergent capabilities promise to extend the reach of high-quality diagnostics to remote populations, improve health management, and reduce health-care costs everywhere.