Medical Device Frontiers: Researchers Develop a New Device for Self-Monitoring
Home-testing kits have made it easier for diabetics to track their conditions. However, such self-monitoring hasn't been possible for people with phenylketonuria (PKU). Engineers at the Georgia Institute of Technology (Georgia Tech, Atlanta) hope to change that by introducing the first home-testing device for PKU patients.
PKU is a genetic metabolic disorder in which the body lacks a liver enzyme (phenylalanine hydroxlase) needed to process phenylalanine, an essential amino acid, into another amino acid (tyrosine) used by the body. Left unconverted, excessive amounts of phenylalanine in the bloodstream are toxic to brain tissue and the central nervous system; if untreated in newborns, PKU can cause brain damage and mental retardation.
Unfortunately, there is no drug that can cure PKU. It can only be treated through diet. Because phenlylalanine is a component of proteins, patients must follow a strict low-protein diet, avoiding meat, fish, eggs, poultry, dairy and soy products, as well as food containing the artificial sweetener aspartame. "When phenylalanine levels become too high, PKU patients can suffer movement disorders, such as tremors, seizures and hyperactivity," says Jeff Sitterle, chief scientist at the Georgia Tech Research Institute and project director for the PKU testing device.
"Blood-testing requirements vary depending on the severity of a patient's condition, but frequent monitoring is especially important for children," adds Sitterle. "The goal is to maintain phenylalanine levels in the blood between 2 and 10 milligrams per deciliter. Pregnant women must also be careful; if phenylalanine levels get too high, it can affect development of the fetus."
In the United States, there are approximately 120 sites where PKU monitoring is conducted. That means frequent testing can be costly and inconvenient for patients who must travel long distances to reach a medical facility.
And, because PKU is considered an "orphan disease" that affects a small sector of the population, Sitterle says large pharmaceutical companies haven't pursued a home test for the disease.
"Incidence of PKU varies around the world," says Richard Shunnarah, president of MetGen Inc. (Atlanta), which is developing blood-monitoring devices for metabolic genetic disorders. In the United States, PKU occurs in about one in 10,000 births. But, the disease varies from a low of 1 in 100,000 births in Japan to a high of 1 in 2,600 births in Turkey.
"PKU patients can keep records of what they eat, but there's no way to know what their blood levels are without frequent testing," notes Sitterle, who has a niece with the disease. "A home test will help patients understand how their bodies react to food." In addition, the testing device will store data, providing a history for doctors to review during patients' routine checkups. "That gives doctors a true trend picture, rather than blood levels that might have resulted from patients making a sudden effort to stick to their diet prior to the checkup," adds Sitterle.
The Georgia Tech device operates similar to a blood-glucose home test. A PKU patient pricks his or her finger and then places a drop of blood on a reagent strip inserted in the testing device. Phenylalanine in the blood causes a reaction to take place on the test strip. Then electronics in the device calculate the rate at which the test strip absorbs a specific color of light. This rate indicates the level of phenylalanine in the blood.
"That may sound simple, but it actually requires thousands of measurements and a mathematical algorithm to pinpoint the right section of data to evaluate," explains Tim Strike, associate head of the technology application branch in the Electronic Systems Laboratory at Georgia Tech Research Institute.
He says one of the project's requirements was to keep consumer costs down. That goal was achieved by using off-the-shelf components, which makes the monitoring device cost-effective to produce in smaller numbers. Another challenge was user-friendliness--important because PKU patients range in age and educational levels. That meant keeping display menus and terminology simple, and reducing the number of steps required to operate the device.
"If you have too many steps to follow, it can be confusing for new users--and downright irritating when you use it on a regular basis," says Strike. "We wanted to make this as easy as buying a soft drink from a machine."
MetGen plans to submit an application for FDA approval in early 2005, and begin marketing the PKU home test some time later next year.