Clinical utility of diagnostic tests for rheumatoid factor

Rheumatoid factor by laser nephelometry and Waaler–Rose assay: prognostic value in patients with recent‐onset rheumatoid arthritis

OBJECTIVE

To evaluate the prognostic value of rheumatoid factor (RF), detected in the Waaler-Rose agglutination assay and by nephelometry, in patients with recent-onset rheumatoid arthritis (RA).

METHODS

Consecutive patients with new-onset RA between 1993 and 1997 were followed for a median period of 4.7 years. Clinical data at baseline and drug use during the disease course were recorded. Outcome parameters studied were disease process, damage (erosions, joint surgery, extra-articular manifestations, and new co-morbidity), and death. Cut-off levels for RF were >40 IU/mL (nephelometry) and titres 1:160 (Waaler-Rose haemagglutination).

RESULTS

RF tests were negative by both methods in 22% of RA patients (RF- group), while 33% were RF positive by nephelometry only (RF+ group) and 45% were positive by Waaler-Rose and nephelometry (RF++ group). Baseline clinical and laboratory findings as well as the number of subsequently used disease-modifying anti-rheumatic drugs (DMARDs), the number of patients starting and the time spent on steroid therapy were similar in the three RF groups. Odd ratios for death (n = 23), erosions (n = 62), and serious extra-articular disease manifestations (EAMs) (n = 13) as well as patient survival, erosion-free or surgery-free survival rates did not differ between the RF groups. Only rheumatoid nodules were more frequent in RF++ patients.

CONCLUSION

The baseline presence of RF by either Waaler-Rose or nephelometry was not associated with differences in drug therapy, morbidity other than rheumatoid nodules, or mortality in RA patients in the first 5 years of disease. Being immunoglobulin M (IgM) RF positive thus had little impact on RA patient outcome.

Salivary gland and temporomandibular joint involvement in rheumatoid arthritis: relation to disease activity

OBJECTIVES

To study temporomandibular joint (TMJ) involvement, salivary gland dysfunction and oral mucosal lesions in rheumatoid arthritis (RA), and to investigate the relationship to general disease activity.

SUBJECTS AND METHODS

The TMJ dysfunction index (D(i)), mean salivary flow and disease activity score (DAS28), were calculated for 50 RA-patients, and 23 non-RA patients (controls).

RESULTS

Median D(i) was 5.5 (range: 0-21) for the RA-patients compared with 2.0 (range: 0-9) for the controls (P < 0.0001). Pain on movement of the TMJ (P = 0.015), muscular pain (P = 0.006), TMJ pain (P = 0.019) and D(i) as a total (P = 0.009), significantly correlated with DAS28. Mean resting whole saliva (RWS) flow was 2.6 (s.d. 2.4) ml per 15 min for the RA-patients and 4.5 (s.d. 3.0) for the controls (P = 0.003). RWS correlated positively with haemoglobin (P = 0.021) and negatively with Westergren erythrocyte sedimentation rate (ESR) (P = 0.029). No major differences in frequency of oral mucosal lesions were seen between RA-patients and controls.

CONCLUSIONS

Higher frequency of TMJ and salivary gland dysfunction in RA-patients compared with controls has been demonstrated. RA disease activity is associated with hyposalivation and TMJ dysfunction.

Immunoglobulin G and A antibody responses to Bacteroides forsythus and Prevotella intermedia in sera and synovial fluids of arthritis patients

The objective of the present study was to investigate immunoglobulin G (IgG) and IgA antibody immune responses to Porphyromonas gingivalis, Prevotella intermedia, Bacteroides forsythus, and Candida albicans in the sera of patients with rheumatoid arthritis (RA), the synovial fluid (SF) of patients with RA (RA-SF samples), and the SF of patients without RA (non-RA-SF samples). An enzyme-linked immunosorbent assay was used to determine IgG and IgA antibody levels in 116 serum samples from patients with RA, 52 RA-SF samples, and 43 non-RA-SF samples; and these were compared with those in SF samples from 9 patients with osteoarthritis (OA-SF samples) and the blood from 100 donors (the control [CTR] group). Higher levels of IgG antibodies against B. forsythus (P < 0.0001) and P. intermedia (P < 0.0001) were found in non-RA-SF samples than in OA-SF samples, and higher levels of IgG antibodies against B. forsythus (P = 0.003) and P. intermedia (P = 0.024) were found in RA-SF samples than in OA-SF samples. Significantly higher levels of IgA antibodies against B. forsythus were demonstrated in both RA-SF and non-RA-SF samples than in OA-SF samples. When corrected for total Ig levels, levels of IgG antibody against B. forsythus were elevated in RA-SF and non-RA-SF samples compared to those in OA-SF samples. Lower levels of Ig antibodies against B. forsythus were found in the sera of patients with RA than in the plasma of the CTR group for both IgG (P = 0.003) and IgA (P < 0.0001). When corrected for total Ig levels, the levels of IgG and IgA antibodies against B. forsythus were still found to be lower in the sera from patients with RA than in the plasma of the CTR group (P < 0.0001). The levels of antibodies against P. gingivalis and C. albicans in the sera and SF of RA and non-RA patients were comparable to those found in the respective controls. The levels of IgG and IgA antibodies against B. forsythus were elevated in SF from patients with RA and non-RA-SF samples compared to those in OA-SF samples. Significantly lower levels of IgG and IgA antibodies against B. forsythus were found in the sera of patients with RA than in the plasma of the CTR group. This indicates the presence of an active antibody response in synovial tissue and illustrates a potential connection between periodontal and joint diseases.

Modelling autoimmune rheumatic disease: a likelihood rationale

Immunoglobulins (Igs) and autoantibodies are commonly tested in sera from patients with suspected rheumatic disease. To evaluate the clinical utility of the tests in combination, we investigated sera from 351 patients with autoimmune rheumatic disease (ARD) rheumatoid arthritis (RA), systemic lupus erythematosus (SLE) and Sjögren's syndrome (SS) and 96 patients with nonautoimmune rheumatic disease (NAD) (fibromyalgia, osteoarthritis, etc.). Antinuclear antibodies (ANA), rheumatoid factor (RF), antibodies against DNA and extractable nuclear antigens (anti-ENA), IgG, IgA and IgM were measured for all patients. Logistic regression analysis of test results was used to calculate each patient's probability for belonging to the ARD or NAD group as well as likelihood ratios for disease. Test accuracy was investigated using receiver-operating characteristic (ROC) plots and nonparametric ROC analysis. Neither concentrations of IgG, IgA, IgM, anti-DNA nor anti-ENA gave a significant effect on diagnostic outcome. Probabilities for disease and likelihood ratios calculated by combining RF and ANA performed significantly better at predicting ARD than utilization of the diagnostic tests in isolation (P < 0.001). At a cut-off level of P = 0.73 and likelihood ratio = 1, the logistic model gave a specificity of 93% and a sensitivity of 75% for the differentiation between ARD and NAD. When compared at the same level of specificity, ANA gave a sensitivity of 37% and RF gave a sensitivity of 56.6%. Dichotomizing ANA and RF as positive or negative did not reduce the performance characteristics of the model. Combining results obtained from serological analysis of ANA and RF according to this model will increase the diagnostic utility of the tests in rheumatological practice.