WASHINGTON — Diabetics are about to get a science fiction-like way to measure their blood sugar painlessly: The government approved a wristwatch-looking device Thursday that uses tiny electric currents to monitor diabetes.
The long-awaited GlucoWatch won't completely replace diabetics' dreaded finger-prick blood tests because the watch is not perfect, the Food and Drug Administration warned. Nor is it for children, a disappointment to parents anxiously awaiting pain-free alternatives to sticking little fingers.
But it does promise adult diabetics important benefits: supplementing finger testing for more frequent glucose monitoring that may keep them healthier, and sounding an alarm if blood sugar hits dangerous levels — possibly lifesaving if that happens during sleep.
"This particular device is going to allow patients to have an early warning signal" that less frequent blood tests don't allow, explained Dr. Bernard Statland, FDA's medical device evaluation chief.
Manufacturer Cygnus Inc., which struggled three years to win FDA approval of the prescription-only GlucoWatch, revealed Thursday that most people will have to wait until around the year's end to buy it.
Cygnus hasn't scaled up manufacturing to make enough, so immediate sales will be to about 150 patients in test marketing to ensure diabetics use it properly.
The GlucoWatch will cost $400, plus a $4 to $5 disposable sensor that the patient must replace every 12 hours. To get a doctor's prescription for a watch, the FDA is requiring that patients be trained to use it and pass a quiz.
The GlucoWatch is a good first step toward diabetics' ultimate goal of continual, painless glucose monitoring, said Dr. Christopher Saudek, president-elect of the American Diabetes Association.
Supplementing fingerstick tests can be helpful, and some diabetics have longed for the watch, he said. But, Saudek cautioned, "it still has development to go before it becomes something that would be used for all comers."
Some 16 million Americans, the vast majority adults, have diabetes, meaning their bodies cannot properly regulate blood sugar, or glucose.
They check their levels by pricking a finger and placing a drop of blood on reactive strips.
Frequent testing, four to eight times a day, helps maintain tight control over glucose levels and lower chances of debilitating complications such as blindness, kidney disease and nerve damage.
But the tests are painful and inconvenient, leading many to test only twice a day.
Even frequent testers cannot know if glucose soars or drops between testing or during sleep.
To use the prescription-only GlucoWatch, patients slide a thin plastic sensor onto the watch's back.
Small electric currents extract a tiny portion of glucose from fluid in skin cells instead of blood, measuring it every 20 minutes.
Never use insulin or make medication adjustments without first double-checking a GlucoWatch reading with a fingerstick test, the FDA warned.
While the GlucoWatch generally is as good as blood tests, a quarter of the time its readings can differ by about 30 percent.
That's particularly a concern in detecting hypoglycemia, blood sugar that drops below a measure of 70.
But Cygnus says patients can program the GlucoWatch to sound an alarm before glucose plummets too low, giving time for a blood test.
Also, the watch won't measure if the patient's arm becomes too sweaty and is less effective at detecting very low glucose than very high levels, the FDA cautioned.
For now, only adults can use it because doctors don't know if GlucoWatch's skin cell fluid measurements correlate to blood measurements in children as they do in adults, cautioned FDA medical reviewer Pat Bernhardt.
Cygnus is studying the GlucoWatch with children.