Consecutive sera (
n = 409) were obtained between October 2005 and February 2006 from patients visiting the rheumatic outpatient clinic (Clinical Department of Internal Medicine) of the Innsbruck Medical University (Innsbruck, Austria) and stored until final use. Frozen sera (
n = 222) from patients with known inflammatory rheumatic diseases obtained between 2003 and 2005 were randomly selected and included in the analysis. The final diagnosis was used as the reference standard and was obtained by chart review. Unclear cases were discussed by three investigators (C Dejaco, C Duftner, and MH) and excluded if no definite diagnosis could be reached (
Additional File 1). One hundred and sixty-four patients were diagnosed as having RA that met at least four out of the seven criteria according to the 1987 ACR classification [
2]. In the rest of the cases, the following diagnoses were made: osteoarthritis (OA [
n = 120]), polymyalgia rheumatica and/or giant cell arteritis (PMR/GCA [
n = 80]) [
21], spondyloarthritis (SpA [
n = 36], including psoriatic arthritis [
n = 10] [
22], ankylosing spondylitis [
n = 9] [
23], and colitis-associated/undifferentiated SpA [
n = 17]) [
24], or other inflammatory rheumatic or non-inflammatory disease (
n = 67; connective tissue disease [
n = 12], crystal arthopathy [
n = 4], fibromyalgia [
n = 9], mechanical back pain or enthesopathy [
n = 29], virus infection-associated arthralgia [
n = 6], and myelodysplastic syndrome [
n = 7]). Demographic, clinical, and serological data of patients with RA were obtained by chart review (Table
1). Also, data on the serum levels of immunoglobulin (Ig) M-RF (IgM-RF), which were routinely determined by a nephelometric method (normal values 0–13 U/ml), were retrieved by chart review. The mean ages of patients with RA and patients with non-RA were 60.4 (± 12.0) and 58.5 (± 15.7) years (not significant), respectively. In the RA group, there were slightly more women (85.4%) than in the control group (76.2%;
p = 0.026 according to the χ
2 test with Yates correction). Patients with RA were under current treatment with single or combined disease-modifying anti-rheumatic drugs (methotrexate [
n = 95], leflunomide [
n = 21], azathioprine [
n = 3], sulfasalazine [
n = 13], hydroxychloroquine [
n = 13], cyclosporine A [
n = 2], and
Escherichia coli extract OM-89 [
n = 8]) alone or in combination with corticosteroids (
n = 84), and tumour necrosis factor-α blocking agents (infliximab [
n = 2], etanercept [
n = 6], adalimumab [
n = 10], or anakinra [
n = 2]). No association was found between disease duration and markers of disease activity (data not shown). The study was approved by the local ethics committee. Written and informed consent was obtained from each patient.
Table 1
Clinical characteristics of patients with rheumatoid arthritis (n = 164)
Age | 60.4 (12.0)a |
Female, n (%) | 140 (85.4) |
Disease duration (n = 153) | |
<1 year, n (%) | 23 (15.0) |
1–5 years, n (%) | 45 (29.4) |
>5 years, n (%) | 85 (55.6) |
DAS-28 (n = 69) | 3.3 (1.5)a |
Swollen joint count (n = 137) | 1 (0–23)b |
Tender joint count (n = 92) | 1 (0–28)b |
Patients' global assessment (VAS) (n = 56) | 23.2 (23.5)a |
ESR (mm/first hour) (n = 152) | 28.8 (19.3)a |
CRP (mg/l) (n = 160) | 13.9 (23.2)a |
IL-6 (pg/ml) (n = 74) | 111.0 (292.2)a |