Study: Testing for joint substance in blood might improve diagnosis of osteoarthritis

02/24/05

CHAPEL HILL -- Measuring a biological chemical called hyaluronan found naturally in joints and the fluid that lubricates cartilage might enable doctors to diagnose osteoarthritis of the knee and hip earlier or more accurately, a new study concludes. Improving diagnosis of the painful inflammatory disorder should become increasingly important as baby boomer age, doctors say.

The research, conducted at the University of North Carolina at Chapel Hill and in Johnston County, N.C., revealed that levels of the chemical, also known as HA, in blood samples corresponded with how advanced osteoarthritis was in a group of rural patients, both blacks and whites.

"Our study shows statistically significant differences in average levels of serum hyaluronan (HA) between individuals with osteoarthritis of the knee as shown on X rays and those without knee or hip osteoarthritis," said study director Dr. Joanne M. Jordan. "Serum HA levels not only were associated with the presence of osteoarthritis but also showed a trend of increasing values as severity of the disease increased."

Jordan is associate professor of medicine and orthopaedics at the UNC School of Medicine. Also associate director of the Thurston Arthritis Research Center, she is principal investigator for the long-term Johnston County Osteoarthritis Project. That investigation is the largest of its kind ever done and involves more than 3,000 volunteers whose health and experiences with arthritis doctors follow and analyze.

A report on the findings appears in the January issue of Arthritis & Rheumatism, a journal published by the American College of Rheumatology.

Besides Jordan, UNC schools of medicine and public health authors are Dr. Alan L. Elliott, a rheumatology fellow; Dr. Jordan Renner, professor of radiology and allied health sciences; and Anca D. Dragomir and Gheorghe Luta, doctoral students in epidemiology and biostatistics, respectively.

Dr. Virginia B. Kraus, associate professor of medicine, and Thomas Stabler, both at Duke University, Dr. Charles D. Helmick of the Centers for Disease Control and Prevention and Dr. Marc C. Hochberg of the University of Maryland also participated in the study.

Hyaluronan is produced by cells of what is called the extracellular matrix, Jordan said. It is thought to contribute to lubricating joints, a process without which walking and running would be unbearably painful. Earlier work suggested HA might serve as a sign, or biomarker, of osteoarthritis.

"Our study is unique in that it consisted of a large, ethically diverse, population-based sample of African Americans and Caucasians and incorporates five definitions of osteoarthritis as shown on X rays," she said. "This was the first study of hyaluronan and osteoarthritis to include African Americans and to consider how other health problems commonly occurring with osteoarthritis might confound the relationship between serum HA and osteoarthritis."

The researchers studied 753 subjects, including 455 with osteoarthritis in their knees. Volunteers ranged in age from about 51 to 72 and averaged almost 62. About 39 percent suffered from high blood pressure, the most common other illness. The least common was cancer.

Average serum HA levels correlated with age, Jordan said. Whites and men showed higher levels than blacks and women, which could reflect genetic or physiologic factors. Such sex and racial differences would need to be taken into account when determining the usefulness of HA and other potential biomarker testing.

Medical scientists have known for the past decade that levels of an important protein known as COMP were higher in cartilage, ligaments, tendons and joint lubricating fluid of whites with osteoarthritis than in whites without the painful, degenerative illness, Jordan said.

In 2003, she and her UNC colleagues showed for the first time that the same thing is true in blacks. They also found average levels of the protein to be higher in blacks -- both patients and others -- than in whites and higher among white men than among white women.

"These discoveries are likely to be important in the search for better ways to predict who is at strong risk of developing osteoarthritis, who has it already and whose illness is most likely to progress," Jordan said.

Osteoarthritis, the most common form of arthritis, afflicts almost a million North Carolinians and more than 21 million people nationally, including many adults over age 65, the physician said. Some estimates suggest that as many as 70 million Americans will suffer from some form of arthritis within the next 20 years as baby boomers age.

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