C-reactive protein not useful for predicting early OA

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Rheumawire

Mar 12, 2004

C-reactive protein not useful for predicting early OA

San Francisco, CA - C-reactive protein (CRP) is not a useful indicator

of early osteoarthritis, according to researchers from Duke University.

They found that levels of CRP were strongly associated with body mass

index (BMI), and on statistical analysis, they found that this

association entirely explained any link that had been seen between CRP

levels and OA in their study.

The new findings, from a study of 670 ethnically diverse

patients with OA, were presented earlier this week at the Orthopaedic

Research Society 2004 meeting in San Francisco. Lead investigator Dr

Virginia Kraus (Duke University Medical Center, Durham, NC) says

previous studies suggesting that CRP may be a predictive marker for OA

had not taken into account either weight or ethnicity of the patients

and were focused mainly on women. In their investigation, Kraus et al

found a strong association between CRP and BMI and also found higher

levels of CRP in African Americans and women in general. Kraus says all

3 factorsweight, ethnicity, and gendermust be taken into account when

interpreting CRP levels in diagnosing common chronic disorders.

The 670 participants of this study were recruited from the ston

County Osteoarthritis Project, directed by Dr Joanne Jordan at the

University of North Carolina at Chapel Hill. The sample was 49% American

African and 41.5% male, with an average age of 62 years. The mean BMI

was 30, so most of the patients were overweight (normal BMI is 18.5 to

25).

Any patients with self-reported cancer, rheumatoid arthritis, or gout

had already been excluded, but many of the trial participants, in

addition to having OA, also suffered from a concomitant disorder, as

follows: 10% had chronic pulmonary disease, 21% cardiovascular disease,

38% hypertension, and 13% diabetes. In addition, 19% were current

smokers and 37% were taking arthritis pain medications. CRP levels in

serum samples were measured using the UBI Magiwel Enzyme Immunoassay

(United Biotech Inc, Mountain View, CA).

Serum CRP was significantly higher in African Americans, women

(p<0.0001), and patients with chronic pulmonary disease and was strongly

associated with BMI (p<0.0001), but not with age, cardiovascular

disease, or current smoking.

" CRP levels were also strongly positively associated with all

definitions of osteoarthritis based on radiographic status (p<0.0001),

with the levels increasing as the severity of the disease increased, "

says Kraus. " However, after statistical analysis, all these associations

between CRP levels and degree of osteoarthritis were explained entirely

by BMI differences, " she points out. " For that reason, we do not think

that CRP levels can be a useful predictor of osteoarthritis. "

Kraus tells rheumawire that the association between CRP and BMI has been

reported previously, but, even so, most studies investigating CRP in

various chronic conditions, even those looking at cardiovascular

disease, have not recorded BMI. A new finding was the high level of CRP

in African Americans, which was independent of BMI, cardiovascular

disease, and osteoarthritis. This shows the importance of taking

ethnicity into consideration, she says. " It now appears that CRP is not

a simple measure of inflammation, it's actually rather complex and has

associations with several different factors, " she says.

There's been a lot of interest recently in measuring CRP, she says,

mainly because new, supersensitive assays have become available, but

there's still a lot of work needed to understand what CRP levels are

saying about disease status and inflammation. So far, it appears that

patients with osteoarthritis have CRP levels that are abnormal but

rather low, whereas patients with rheumatoid arthritis have levels that

are abnormal but not quite as low, Kraus comments.

Kraus and colleagues speculate that interleukin-6 may explain the link

between CRP and BMI. Extensive studies have shown that IL-6 is the

principal inducer of the CRP gene, and the fact that adipose tissue is a

major source of IL-6 (especially the " bad " fat that collects around the

waist) probably accounts for the strong relationship between CRP and

BMI, she says. " Abdominal fat has been described as a factory that

produces inflammatory cytokines, including IL-6, which raises levels of

CRP, " she tells rheumawire. Intensive exercise alters fat metabolism and

diminishes production of these cytokines, which in turn leads to a

decrease in CRP, and so monitoring changes in CRP may be a useful way of

checking whether patients are adhering to prescribed exercise regimens,

she says.

Zosia Chustecka

Source

1. Stabler TV, Jordan JM, Luta G, et al. Presentation: Serum C-reactive

protein levels and osteoarthritis. San Francisco, CA: Orthopaedic

Research Society: 2004 meeting; March 7-10, 2004:Abstract 0948.

I'll tell you where to go!

Mayo Clinic in Rochester

http://www.mayoclinic.org/rochester

s Hopkins Medicine

http://www.hopkinsmedicine.org