By Julie Steenhuysen

CHICAGO (Reuters) - A person's long-term risk of heart disease is better assessed by a pair of studies, as performing only one may miss a dangerous buildup of calcium in arteries, U.S. researchers said on Monday.

They said about half of all patients in a 10-year study who had normal results on a nuclear stress test known as SPECT were found to have significant buildup of calcium on the walls of their arteries when they did a heart CT.

"Typically, when a patient presents with chest pain and the (SPECT) test result is normal, we tell them everything looks fine, but this may not be the case," Dr. John Mahmarian of the Methodist DeBakey Heart and Vascular Center in Texas, who led the study, said in a statement.

He said if a large amount of calcified plaque is found on artery walls -- something that can't be seen in SPECT imaging -- the patient has a high long-term risk of having a heart attack or stroke.

"Based on our findings, using both tests to define risk is better than either test alone," Mahmarian said in a statement.

Nuclear stress tests using single-photon emission computed tomography, or SPECT, examine blood flows to the heart. People with a normal result are generally thought to have less than a 1 percent chance of having a heart attack within a year.

Computed tomography or CT scans use special X-ray equipment and sophisticated computers to measure calcified plaque in the heart arteries. These tests can detect varying degrees of blockages in the heart.

Both tests expose patients to radiation.

Mahmarian's team followed 1,126 patients with no previous history of coronary artery disease whose doctors had already received both tests.

They found people who were deemed low risk by the SPECT test were three times more likely than others to have a heart attack during the study period if they had high calcium scores.

For these patients, a high calcium score was an even stronger predictor of having a heart problem than diabetes.

They said people with a normal SPECT who have other risk factors that put them at risk for heart trouble -- such as smoking, high cholesterol, high blood pressure, diabetes or a family history of heart trouble -- would benefit from the extra test.

"We're not recommending doing this to everybody. The patient has to have clinical risks," Dr. Su Min Chang of the Methodist Hospital, who worked on the study, said in a telephone interview.

He said people who get a normal stress test might get a false sense of security. Adding the calcium test could give them a better picture of their long-term risk.

The team did not look at whether the two-test strategy is cost effective but they said such studies are needed.

Imaging tests are a major source of escalating health costs and curbing excessive use of such tests is a major target of health reform in the United States.

(Editing by Cynthia Osterman)

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