WASHINGTON — Diabetes care is undergoing a transformation: Thousands of patients are switching from a few finger pricks a day to track their disease to new sensors that keep guard around-the-clock.

The last six months brought boosts to the technology as federal health officials approved children's use of a sensor that works for three days in a row — and cleared the longest-lasting version yet, a seven-day model, for adults.

The ultimate goal is to create an "artificial pancreas," pairing such sensors with implanted pumps that would automatically dispense insulin to make a diabetic's blood sugar better resemble a healthy person's.

That's still years away. For now, the hope is that these under-the-skin sensors will empower the most vulnerable patients — those who require insulin injections — to make changes that better control their disease. Perhaps more importantly, they come with alarms that can sound in time to avoid dangerously high or low blood-sugar levels.

"It really catches problems before they're problems," said Katie Clark of Grandville, Mich. She bought a sensor for her 7-year-old daughter, and no longer has to wake up in the middle of the night to spot-check whether Ellie's OK.

But these "continuous glucose monitors" cost up to $1,000, plus at least $350 a month for supplies. Insurance coverage is hit-or-miss: Some pay, but many refuse pending proof that the sensors live up to their promise of better health.

Some short-term studies show that users greatly improve control of their blood sugar, while other studies have found little impact. Why the discrepancy? Diabetics who do the worst job fighting their disease aren't going to put in extra effort to improve just because of a sensor, said Dr. Irl Hirsch of the University of Washington.

Hirsch presented research at a recent diabetes meeting suggesting that the sensors will most benefit patients who can't lower their blood sugar to optimal levels — a score below 7 on a test called the A1C — despite following best-care guidelines. He finds the sensors help lower A1Cs between 7 and 8.5, but not those that start out higher.

By November, scientists should complete enrollment of 450 diabetics into a study funded by the Juvenile Diabetes Research Foundation to address insurers' questions on best use of the sensors. Preliminary results are due next year.

Some 21 million Americans have diabetes, meaning their bodies cannot properly regulate blood sugar, or glucose. About 5 million inject insulin, a hormone that converts glucose into energy, to treat their diabetes — including the roughly 2 million with Type 1 diabetes who require those shots to live.

High glucose levels damage blood vessels and nerves, leading to blindness, kidney failure, amputations and heart disease. Frequent testing — pricking a finger for a blood test four to eight times a day — helps patients maintain tighter glucose control, thus lowering risk of those complications. But few diabetics test that often, and frequent testers cannot know if glucose soars or plummets between tests or during sleep.

With the new technology, diabetics use a needle to insert a sensor under the skin of the side or abdomen every three or seven days. The sensors wirelessly beam readings to a pagerlike device every 5 minutes.

Available now are Medtronic Inc.'s three-day Real-Time monitor — sold by itself, for adults or children, or together with a manually adjustable insulin pump — and DexCom Inc.'s STS-7 seven-day monitor for adults. A five-day competitor from Abbott Laboratories is in development.

Users require training. For example, it takes up to 15 minutes for a glucose change in blood to be reflected in the cell fluid that sensors measure.

When Ellie Clark's sensor showed that her morning oatmeal made her glucose soar to a level of 300, her mother started giving her entire morning insulin booster before breakfast. Now Ellie's morning jump is to a moderate 200.

Ellie's average glucose dropped so much after six months of sensor use that Katie Clark, also a Type 1 diabetic, bought one for herself.