Kristin Wall
Nov 18, 2011
Featured

Measuring glucose with tears instead of blood

Imagine having to prick your finger up to ten times a day, every day of your life, to stay alive. For about 25.8 million American adults and children living with diabetes today, this painful and inconvenient practice is a reality. At present, the finger-pricking method is the primary test available to monitor diabetics’ blood glucose levels in a continuous effort to avoid hypoglycemia and other deadly complications of the disease.

 

Some diabetics may opt to forgo finger pricking and instead utilize ongoing monitoring systems, such as insulin pumps. An insulin pump consists of a cartridge of insulin that may be clipped to the patient’s belt, and flexible tubing that attaches the insulin reservoir in the cartridge to a cannula, which is inserted under the patient’s skin on his hip or stomach area.

 

Although the insulin pump allows users to avoid multiple finger-pricks every day, the sensor must still be replaced every 3-7 days, depending on the type of sensor, using a needle to insert the cannula. Under either method, treatment is invasive and can be painful.

 

Scientists have been hard at work trying to develop a non-invasive blood glucose-monitoring device, but have been unsuccessful until recently. Methods considered include measuring radio waves and bodily fluids through the skin, but these non-invasive tests have yet to match the accuracy of direct blood measurements. When dealing with such minute margins of error, accuracy is the priority, even at the expense of the patients’ comfort.

 

Researchers at the EyeLab Group, the University of Michigan, and the Mayo Clinic, however, believe that they may have found a viable alternative to blood glucose monitoring, and hope to make the test available on the market in the next three to five years. The answer is the eye – the window to your soul, and now also to your glucose levels.

 

In an article published in Analytical Chemistry in late September of this year, researchers described an amperometric needle-type electrochemical glucose sensor intended for tear glucose measurements, to be employed in conjunction with a capillary tube to collect microliter volumes of tear fluid.

 

But don’t let the description scare you – this innovative new system is as easy as touching the sensor to your conjunctiva (the white part of your eye) for five seconds. Nor is this method anything to cry about; the sensor requires only 4-5 microliters of tear fluid for each test, as compared to the 750-1100 microliters of tear fluid the average adult naturally secretes every twenty-four hours, even without chopping onions or listening to Adele’s “Someone Like You.”

 

The sensor operates by immobilizing glucose oxidase contained in the tear fluid sample on a platinum/iridium wire and anodically detecting the liberated hydrogen peroxide from the enzymatic reaction to calculate glucose levels. In tests performed on rabbits, this method produced comparably accurate results to those of traditional blood glucose tests.

 

This is the first non-invasive test to produce such highly accurate results. The only downside to this exciting new testing method is the need for speed and accuracy – the patient must perform the test faster than the tear evaporates from the test strip (this may put patients in the more arid states at a slight disadvantage). Adding a little hustle seems like a small price to pay, however, for keeping your fingers and hips prick-free, and effectively managing this disease.