Signs of heart disease — generally thought to be a disease of middle age — can be seen even in children, cardiologists now know. But risk factors in children and young adults run the risk of being undetected and untreated, largely because of confusion as to who among the young should get screened, and when.

One of the most efficient ways to screen for heart-disease risk is via tests for levels of low-density lipoprotein (LDL, or “bad”) cholesterol. And yet often that screen doesn’t get done.

In a study published in the July-August issue of the Annals of Family Medicine, Dr. Elena Kuklina and colleagues from the Centers for Disease Control and Prevention examined data from the 1999-2006 National Health and Nutrition Examination Survey, a national survey that includes interviews and physical examinations, to see how frequently young adults were getting screened for LDL cholesterol.

Of the 2,587 young adults in the study—men 20 to 35 years old and women 20 to 45 — fewer than 50 percent had been screened. Yet 59 percent of them had heart disease or related conditions such as diabetes or at least one risk factor for heart disease (such as obesity, high blood pressure, smoking or a family history of heart disease before age 50).

The study also reported that 65 percent of young adults with heart disease or related conditions had unhealthily high LDL cholesterol levels, as did 26 percent of those with two or more risk factors, 12 percent with one risk factor and 7 percent with no risk factors.

“This is a big problem,” said Kuklina, a fellow at the CDC’s division of heart disease and stroke prevention. “Heart disease and risk factors are common in young adults, and yet screening rates are low.”

It turns out that doctors themselves don’t know what to do about the screening issue because two different guidelines exist for screening adults for cholesterol. “Doctors are confused about which guideline to follow, and insurance companies may not cover screenings depending on what guidelines they follow,” Kuklina said.

One set of guidelines, supported by the American Heart Association and the National Heart, Lung and Blood Institute, is from the National Cholesterol Education Program. It recommends screening young adults, regardless of risk level, every five years once they turn 20.

Another set of guidelines, by the U. S. Preventive Services Task Force, recommends screening all men 35 and older and all women 45 and older. It recommends earlier screening only if a person already has heart disease or at least one risk factor.

“Neither guideline gives you a clear understanding of how often you should be screening patients,” said Dr. John Gaziano, a preventive cardiologist at the VA Boston Healthcare System.

“When the guidelines were first written, there weren’t many studies about young adults because it wasn’t known that it is a cumulative problem,” Kuklina said. Now, she adds, doctors also know that blood cholesterol levels are influenced by growth and hormone changes, which means that older teens and young adults should be screened more often so as to track blood cholesterol changes.

Government screening guidelines for children also need updating, said Dr. Elaine Urbina, director of preventive cardiology at the Cincinnati Children’s Hospital Medical Center. Guidelines from the National Cholesterol Education Program recommend screening only for those children who have heart disease in their family.

The NCEP children’s guidelines were written in 1992, said Urbina. They are based only on family history, which not every person is aware of, and do not take into account risk factors such as obesity and high blood pressure that are far more prevalent in children today.

The American Academy of Pediatrics issued broader guidelines in 2008 that recommend — in addition to screening kids with a family history of heart disease — screening children whose family history isn’t known or who have other heart disease risk factors such as obesity, high blood pressure or diabetes. Screenings should take place after age 2 but before age 10, the academy said.

And the government’s National Heart, Lung and Blood Institute is currently preparing new guidelines, the Pediatric Cardiovascular Risk Reduction Initiative, which will be released later this year. Urbina, who is involved in crafting them, said that they too will make broader screening recommendations that take into account risk factors other than family history.