A Paper-Based Multiplexed Transaminase Test for Low-Cost, Point-of-Care Liver Function Testing

A paper-based, multiplexed microfluidic assay allows rapid, semiquantitative, visual measurement of transaminases in clinical specimens. Spot-On Toxicity Testing “Just a little pinprick,” Pink Floyd once reassured its listeners. Of certainty, they were not singing about liver function tests. Nevertheless, the soothing lyric can be just as readily applied to paper-based microfluidics, for which only a droplet of blood—from a finger pinprick—can indicate whether a patient has liver toxicity and needs additional care. In a new study, Pollock and colleagues developed a cost-effective, multiplexed paper-based test that measures two enzymes in human blood commonly associated with liver injury: aspartate aminotransferase (AST) and alanine aminotransferase (ALT). Levels of these transaminases are elevated in patients with liver toxicity, such as those on several medications at once (for example, drug “cocktails” for HIV and tuberculosis). In the developing world, limited resources often prevent patients from having access to the automated laboratory tests used in developed countries. To address this unmet need, Pollock et al. created a point-of-care (POC) device that requires only blood and the human eye for analysis. The authors stacked layers of patterned paper containing “test zones” with chemistries specific for measuring AST and ALT. When blood (<35 μl) is spotted on the device, it interacts with reagents to provide, in 15 min, a colorimetric readout that falls into one of three “bins”: <3×, 3×-5×, or >5× the upper limit of normal. This semiquantitative, color-coded message, along with three control zones, informs the doctor of basic facts needed to devise the next treatment steps. Pollock and coauthors tested their paper-based device using 233 blood samples with a range of AST and ALT concentrations. Over all three bins, the device was ≥90% accurate with both serum and whole blood when compared to standard measurement techniques. Costing only pennies to make, these devices can be used at POC to inform clinicians of possible liver injury, without the long waits for results to return from centralized laboratories. With readouts obtained in near real time, patients all over the world can be comfortably reassured of their health. In developed nations, monitoring for drug-induced liver injury through serial measurements of serum transaminases [aspartate aminotransferase (AST) and alanine aminotransferase (ALT)] in at-risk individuals is the standard of care. Despite the need, monitoring for drug-related hepatotoxicity in resource-limited settings is often limited by expense and logistics, even for patients at highest risk. This article describes the development and clinical testing of a paper-based, multiplexed microfluidic assay designed for rapid, semiquantitative measurement of AST and ALT in a fingerstick specimen. Using 223 clinical specimens obtained by venipuncture and 10 fingerstick specimens from healthy volunteers, we have shown that our assay can, in 15 min, provide visual measurements of AST and ALT in whole blood or serum, which allow the user to place those values into one of three readout “bins” [<3× upper limit of normal (ULN), 3 to 5× ULN, and >5× ULN, corresponding to tuberculosis/HIV treatment guidelines] with >90% accuracy. These data suggest that the ultimate point-of-care fingerstick device will have high impact on patient care in low-resource settings.