Diabetics around the world are familiar with the routine of blood glucose testing that requires a prick on the finger to draw blood. Though the inconvenience of drawing blood is a small price to pay for accurate blood sugar control, some diabetics require several tests a day and the frequent pricks can be tiring.
For decades, scientists have pursued alternate methods of blood glucose testing, which could help diabetics improve their control over the disease. Some researchers have targeted tears as a vessel for testing blood glucose, and a recent study published in the journal “Analytical Chemistry” has demonstrated that this may be a viable option.
A research team at the University of Michigan developed a sensor that detects dilute glucose levels in animal tears. They conducted a study using 12 rabbits, demonstrating that the results of glucose tests using tears had similar results to testing using blood samples.
Doctors have made it known that an alternative to the finger-prick blood sugar test would likely be highly successful among diabetics.
“This is an incredibly hot area,” says Dr. George Grunberger, a member of the board of the American Association of Clinical Endocrinologists.
According to Dr. Grunberger, previous research into finding alternative blood sugar testing methods has been enthusiastic, though not always successful.
“People have been trying to read glucose through skin, through measurements attached on the earlobe. There have been machines on the market that got taken off the market because of unreliability and poor reproducibility,” said Dr. Grunberger.
According to the American Diabetes Association, about 25.8 million people in the United States have diabetes; about 7 million of those cases are undiagnosed. Diabetes is characterized by excessive levels of glucose in the bloodstream, which may be caused by a lack of production of the hormone insulin (as in Type 1 diabetes) or a resistance to insulin (as in Type 2 diabetes). Insulin’s job is to transport glucose out of the bloodstream; in diabetics, the body’s inability to use insulin effectively means that glucose remains in the blood.
To combat the effects of chronically elevated blood sugar levels, diabetics must monitor those levels to ensure that they stay in a normal range. For some diabetics, this means testing blood glucose levels “two, three, four or even 10” times a day, says Dr. Grunberger. Since blood sugar levels vary due to diet and physical activity, enough measurements must be taken to ensure proper monitoring.
A team of researchers headed by Jeffrey LaBelle at Arizona State University has previously worked with researchers from the Mayo Clinic to develop blood glucose testing technology that uses tears instead of blood. According to LaBelle, the idea of testing tears dates as far back as 1937, but the fluidity of the liquid makes glucose testing difficult. Tears also contain much less glucose than blood, which means that sensors must be sensitive to small amounts of glucose.
“Levels of glucose in tears have been found to be typically 30-50 times lower than in blood,” wrote the authors on the University of Michigan Study. They noted that physicians would need to establish guidelines for each individual using tears for blood glucose monitoring: “The use of tears as an alternate sample to assess blood glucose in human subjects will likely require that the ratio of glucose in tears and blood be established first for a given individual.”
“The major challenges are evaporation, lower concentration in glucose in tears than blood, lower volume—there’s a lot more blood than tear fluid—and not stimulating the eye; not rubbing it,” says LaBelle.
“Glucose is also a stress responder, so if you stress the eye you can get an inaccurate reading,” he continued.