In the developing world, health care providers often don’t have access to diagnostic technologies like the automated lab tests taken for granted in the resource-rich United States. Specimens often have to be sent to a distant central lab, and it can be weeks before an answer wends its way back.
That’s a tough situation when you’re, say, trying to assess whether a patient is having liver toxicity from a drug, such as drugs used to treat tuberculosis (TB) and HIV. By the time the results come back and indicate you need to stop or switch medications, the patient may be long gone, unable to travel back to the clinic.
For the past four years, Nira Pollock, MD, PhD, associate medical director of the Infectious Diseases Diagnostics Lab at Boston Children’s Hospital, has been working with Diagnostics For All (DFA), a nonprofit organization based in Cambridge, Mass., to develop and test a low-cost diagnostic device that works on the spot, involving just a finger-stick and a square of paper. The technology is all in the paper square—using wax printing and microfluidics techniques initially developed by DFA’s founder, George Whitesides, PhD, of Harvard University.
The result is a multilayered paper device that splits a small blood sample into streams, allowing multiple tests to be done at once without the need for multiple finger-sticks—at a cost of pennies per test.
“The wax creates channels that steer the fluid to certain places as it wicks through the paper,” explains Pollock, also a member of the Division of Infectious Diseases at Beth Israel Deaconess Medical Center (BIDMC). “You put a drop of blood on the center of the device, and a filter separates blood cells from the plasma, which continues down to the layers of paper underneath and wicks to different detection zones. You can spot different reagents in different zones on the paper to perform multiplexed assays.”
Readouts take approximately 15 minutes: the paper in the detection zones changes color to indicate results, which can be matched by eye with a range of expected colors on a chart. Or, through telemedicine, photos of the device (i.e., the paper) can potentially be sent to an expert reader.
DFA and Pollock’s test, evaluating liver function, may emerge as the first clinical diagnostic of this kind. With eradication of TB and HIV as a global priority from the World Health Organization, liver toxicity from regimens used to treat these diseases is important to detect and address. The paper test measures levels of enzymes like AST and ALT, which are good indicators of liver damage.
In a study published in Science Translational Medicine last fall, funded in part by the Boston-based Center for Integration of Medicine and Innovative Technology (CIMIT), Pollock and her DFA colleagues tested the device using 223 blood samples obtained by venipuncture and 10 finger-stick samples from healthy volunteers. The test allowed visual measurements of AST and ALT, in both whole blood and serum, that could be placed into three standard readout categories (AST or ALT less than three times the upper limit of normal (ULN), three to five times the ULN and more than five times the ULN)—with more than 90 percent accuracy.
In a pilot finger-stick study last summer in Vietnam, funded by PATH (Seattle, Wash.), Pollock and collaborators trained nurses to perform the test and interpret the color changes on the devices. In this collaboration between PATH, BIDMC, DFA, the Hospital for Tropical Diseases in Vietnam and the Harvard Medical School AIDS Initiative in Vietnam, the team looked at factors like ease of interpretation, consistency of results and lot-to-lot variability.
With those findings, they’re tweaking and optimizing the paper test and planning a follow-up finger-stick study to take place this summer in collaboration with colleagues from the BIDMC Liver Center and Infectious Diseases clinics, supported in part by another CIMIT grant. The team will also test transmitting pictures of the devices (taken by cellphone cameras) to a remote reader.
“In the future, we could potentially even develop tests like this for home use, like people do glucose monitoring now,” says Pollock.
A big question in point-of-care (POC) diagnostics, she notes, is “how accurate does the test have to be in order to be useful?” Even if the paper test doesn’t perform as well as the gold standard, it could still have a big impact on global health; in equivocal cases, venipuncture samples could still be sent for automated testing.
“People are starting to argue that all the benefits of point-of-care use might ultimately make low-cost POC tests a better choice,” Pollock says.