New research reveals that even individuals who appear to have normal overall cholesterol levels may still face risks from high levels of a type of cholesterol not detected with conventional screenings. This finding may explain why millions of people with "normal" cholesterol levels suffer chest pain or heart attacks annually.

A UT Southwestern study found that 63 men who had suffered heart attacks, chest pain or clogged arteries despite having normal levels of total cholesterol and the so-called "bad" cholesterol had high levels of a form called remnant like particle cholesterol or RLP.

"The majority of people who have heart attacks have what is considered normal cholesterol," said Dr. Ishwarlal Jialal, the senior author of the study published in the American Journal of Medicine. "What we have found may be a powerful new independent risk factor for coronary heart disease."

The study emphasizes the importance of remnant measurement in the management of heart disease. Preliminary research in Japan also indicates that these remnants can be treated with cholesterol-lowering drugs, Dr. Jialal said.

Dr Jialal, a senior investigator in the Center for Human Nutrition and professor internal medicine and pathology, undertook the study with Dr. Sridevi Devaraj, an instructor of pathology, and Dr. Scott Grundy, director of the Center for Human Nutrition. Dr. Gloria Lena Vega, professor of clinical nutrition and health care sciences, and Dr. Richard Lange, associate professor of internal medicine, also participated in the study.

Remnant lipoproteins result from the metabolism of very-low density lipoproteins (VLDL) and chylomicrons -- the major triglycerides that carry lipoproteins. These cholesterol-enriched particles promote plaque formation -- the first step toward arteriosclerosis or hardening of the arteries. High concentrations of RLP cholesterol have been linked to several diseases associated with premature heart disease, such as diabetes and kidney disease.

The study also found that a new cholesterol test, the Remnant Like Particle cholesterol Assay, developed by JIMRO of Japan, reliably assesses RLP cholesterol levels. Researchers examined 63 men with coronary artery disease who had suffered a heart attack or had a history of chest pain or blocked arteries. Each had normal cholesterol levels as defined by the National Cholesterol Education Program, which is a total cholesterol level of less then 240 milligrams per deciliter (mg/dL) and a triglyceride level of less than 200 mg/dL. They were compared to 23 healthy men of similar ages who had higher total cholesterol level and higher low-density lipoproteins (LDL) -- the "bad" cholesterol -- and lower high-density lipoproteins (HDL) -- the "good" cholesterol.

Even though the 63 with coronary heart disease had significantly lower levels of total cholesterol, LDL and HDL than the healthy group, their remnant levels were significantly higher, 33 percent above the control group's levels, Dr. Grundy said."The most dramatic demonstration of the significance of remnant lipoproteins in atherosclerosis is Type III dyslipidemia -- a genetic disorder in which remnant levels are increased with normal LDL cholesterol, resulting in severe atherosclerosis," Dr. Jialal said. "In this study, patients with Type III dyslipidemia had markedly increased remnant levels -- 24 fold -- compared to normal controls."

The Remnant Like Particle Cholesterol Assay is not yet approved by the Food and Drug Administration and is only available at a few centralized labs in the country, including the chemical pathology lab at UT Southwestern, headed by Dr. Jialal.The study was funded in part by Otsuka America Pharmaceuticals, USA.