A study aimed at determining if some children with sickle cell anemia (search) could be weaned off blood transfusion therapy (search) has been halted because two young patients who stopped getting the procedure suffered strokes and others developed a high chance of strokes.

The National Institutes of Health issued a clinical alert Sunday recommending that doctors continue using blood transfusions to reduce the risk of stroke among young sickle cell patients, even though the treatment has its own risk.

The study, called STOP II, was funded by the NIH's National Heart, Lung and Blood Institute and involved 23 U.S. medical centers and two in Canada.

The $15 million study, which started in July 2000, was ended prematurely ended last month after 16 children with sickle cell anemia developed narrowed arteries and other risk factors for strokes after they stopped receiving blood transfusions. Two other children suffered strokes but are recovering, said Dr. Robert Adams, the study's principal investigator and professor of neurology at the Medical College of Georgia.

The study "showed that when transfusions were discontinued after a minimum of 30 months, a significant number of children reverted to high risk" of stroke, the federal agency's clinical alert said.

"I'm disappointed ... that we weren't able to identify a group that we could consistently and safely bring off," Adams said.

Although the blood transfusions are effective, long-term use can cause dangerous accumulations of iron that can lead to heart problems and liver damage.

"We're literally between a rock and a hard place — we need to prevent strokes. At the same time we have a therapy that's not without risk," said Dr. Duane Bonds, the National Institutes of Health's sickle-cell disease coordinator.

The original STOP study, which started in 1995, was halted two years later because transfusions were found to be so effective that researchers recommended all sickle cell children be given the treatment to prevent strokes.

The latest study involved 79 children, age 2 to 18, all of whom had once had a high risk of stroke but whose risk was diminished after years of blood transfusion therapy.

A control group of 37 children continued getting transfusions. Forty-two other children were taken off of transfusions and were closely monitored to check for blockages in brain arteries.

The study was beneficial for eight children, whose stroke risk did not increase even though they had stopped taking blood transfusions for two years during the study.

Sickle cell disease, of which sickle cell anemia is one form, is an inherited blood disorder that affects red blood cells, which sometimes become sickle- or crescent-shaped and cannot easily pass through small blood vessels. The disease mostly affects blacks.

Doctors aren't sure why sickle-cell anemia results in a higher stroke risk.

Adams said it's also not exactly known why transfusions can reduce a patient's stroke risk. The original STOP study found the risk of a first stroke was reduced by 90 percent.

However, transfusions can take four to five hours. And along with iron accumulation, they can expose patients to blood-borne infections.

"It takes a whole day, it's a tedious task," Channelle Allen of Augusta, Ga., said of the transfusions that her 11-year-old daughter Tisha has received. Tisha was one of the patients who developed a high stroke risk after ending transfusion therapy during the STOP II study and has resumed receiving the treatment.

"I didn't want her to go back on blood (transfusions) but it was better for her," Allen said. "I was extremely scared. It's terrifying when a child can't tell you the exact problem they're having — all they can tell you is they're in pain."