Clinical utility of the anti-CCP assay in patients with rheumatic diseases

Anti-CCP: history and its usefulness

Antibodies directed to cyclic citrullinated peptides (anti-CCP) are highly specific for rheumatoid arthritis (RA) and can easily be detected in sera by using commercially available immunoassays. The second version of the anti-CCP test (anti-CCP2) demonstrated high specificity (89-98%) and good sensitivity (41-88%) for RA. Commercially available ELISA methods from three different companies are on the market. All three CCP2 assays show similar results as all CCP2 assays use the same antigen-coated plates. This study was an evaluation of a new automated method for the determination of anti-CCP2 in a routine laboratory setting. Five hundred and fourty three serum samples were tested for anti-CCP2 within normal routine diagnostic using a commercially available ELISA and retested with a prelaunch version of a new and fully-automated method (EliA™). The results were comparable. The new automated assay is easy to use and demonstrated a diagnostic sensitivity of 80% and specificity of 97%.

Diagnostic and prognostic significance of autoantibodies in early rheumatoid arthritis

A positive rheumatoid factor (RF) test has been included as one of the criteria for the diagnosis of rheumatoid arthritis (RA) according to the 1987 classification criteria of the American College of Rheumatology (ACR). During the past 20-30 years many different autoantibodies have been described in patients with RA. The presence of some of the autoantibodies in RA directed against various autoantigens, such as anti-neutrophil cytoplasmic antibodies, anti-nuclear antibodies, antibodies against interleukin-1 (IL-1), anti-cardiolipin antibodies, and antibodies against oxidized low density lipoprotein, is not specific for RA and these are not discussed here. This review summarizes the most relevant autoantibodies, and discusses their sensitivity, specificity, and possible diagnostic and prognostic significance in early RA. The antibodies are presented with the two clinically most relevant antibody tests first, followed by others in alphabetic order.

Antibodies against cyclic citrullinated peptide (CCP) in psoriatic patients with or without joint inflammation

OBJECTIVE

To compare the prevalence of anti-CCP antibodies in psoriatic patients with and without joint inflammation, patients with early RA, and controls.

METHODS

Anti-CCP antibodies (cut off level 5 U/ml) were measured in 160 patients with psoriatic arthritis (PsA), 146 patients with psoriasis but no arthritic disease, 101 patients with early RA, and 102 healthy controls by ELISA.

RESULTS

11 (7%) patients with PsA, 75 (74%) patients with early RA, 2 (2%) healthy controls (2%), and 1 (0.7%) patient with psoriasis without arthritis had anti-CCP antibodies above the cut off level. The presence of anti-CCP antibodies was not related to radiological changes and/or deformity and functional impairment in PsA. 8/11 patients with PsA and anti-CCP antibodies had a polyarthritic disease, and all fulfilled the ACR criteria for RA at 4 year follow up. Five of these 8 patients also had manifestations such as dactylitis, DIP involvement, radiological changes associated with PsA, and/or enthesitis. In multiple logistic regression analysis with polyarthritis as the dependent variable, anti-CCP antibodies and rheumatoid factor significantly distinguished RA from PsA.

CONCLUSIONS

Anti-CCP antibodies were more prevalent in patients with PsA than in patients with psoriasis without arthritis, but less prevalent than in patients with early RA. Patients with PsA positive for anti-CCP antibodies more often had polyarthritic disease, but the presence of anti-CCP antibodies did not relate to radiological changes and/or deformity and functional impairment.

Diagnostic Tests for Rheumatic Disease: Clinical Utility Revisited

Establishing a diagnosis of systemic rheumatic disease requires an integration of a patient's symptoms, physical examination findings, and the results of diagnostic testing. There is often a temptation by clinicians to rely heavily on objective measures such as the presence or absence of an autoantibody. Medical textbooks and the medical literature may overestimate the diagnostic utility of many commonly ordered tests for rheumatic disease because the tests are usually analyzed among patients with established rheumatic disease rather than among patients with an uncertain cause of symptoms as is common in practice. Few diagnostic tests are highly sensitive, though the antinuclear antibody in systemic lupus erythematosus (SLE) and the erythrocyte sedimentation rate in temporal arteritis are notable exceptions. Conversely, few diagnostic tests are highly specific; anti-proteinase-3 and antimyeloperoxidase antibodies (types of antineutrophilic cytoplasmic antibodies) among patients with Wegener granulomatosis (and related vasculitides) and anti-double-stranded and anti-Smith antibodies among patients with SLE may be particularly helpful in the proper clinical settings due to their high specificity. Anticitrullinated cyclic protein (anti-CCP), a newly described autoantibody that may be highly specific for rheumatoid arthritis, requires additional study as its utility in clinical practice is uncertain.

The effect of etanercept on anti-cyclic citrullinated peptide antibodies and rheumatoid factor in patients with rheumatoid arthritis

OBJECTIVE

To evaluate the changes in anti-cyclic citrullinated peptide antibodies (anti-CCP) and rheumatoid factor (RF) following etanercept treatment in patients with rheumatoid arthritis.

METHODS

The study included 90 patients with rheumatoid arthritis who failed treatment with disease modifying antirheumatic drugs (DMARDs). All patients were allowed to continue treatment with DMARDs; 52 of them received etanercept as a twice weekly 25 mg subcutaneous injection for three months, and the others did not. Serum samples were collected at baseline and one month intervals during the treatment course. The serum levels of anti-CCP and RF were tested by enzyme linked immunosorbent assay and nephelometry, respectively.

RESULTS

At baseline, 45 of the 52 etanercept treated patients (86.5%) and 32 of the 38 controls (84.2%) were positive for anti-CCP. Tests for RF were positive in 78.9% and 84.2% of patients with or without etanercept treatment, respectively. The serum levels of anti-CCP and RF decreased significantly after a three month etanercept treatment (p = 0.007 and p = 0.006, respectively). The average decrease from baseline calculated for each individual patient in the etanercept treated group was 31.3% for anti-CCP and 36% for RF. The variation in anti-CCP was positively correlated with the variation in disease activity, swollen and tender joint counts, RF, and C reactive protein.

CONCLUSIONS

Etanercept combined with DMARDs leads to a much greater decrease than DMARDs alone in the serum levels of anti-CCP and RF in rheumatoid arthritis, compatible with a reduction in clinical disease activity.

Autoantibodies to citrullinated proteins in rheumatoid arthritis: clinical performance and biochemical aspects of an RA-specific marker

Rheumatoid arthritis (RA) is a common, systemic autoimmune disease of which the exact etiology is not known. In the past 10 years, substantial progress has been made in the identification of the antigens specifically recognized by the autoantibodies of RA patients. A central factor in this respect is citrullination, a form of post-translational modification that is strongly associated with autoimmunity in RA. Here, we summarize and discuss our current knowledge on (i) autoantibody systems in RA, (ii) the occurrence of peptidylarginine deiminases and (iii) citrullinated proteins in natural and diseased environments, and (iv) genetic factors involved in RA that may influence the generation and presentation of citrullinated proteins and the resulting antibody production against these modified proteins. Citrullination of proteins may play a key role in the initiation and/or the progression of RA. The onset of citrulline-specific autoimmunity in RA is probably mediated by both environmental and genetic factors, and future studies will learn whether therapeutic intervention at the level of citrullination may provide new possibilities to treat RA.

Antibodies against cyclic citrullinated peptides in patients affected by rheumatoid arthritis before and after infliximab treatment

To evaluate antibodies against cyclic citrullinated peptides (anti-CCP) together with rheumatoid factor (RF), antinuclear antibodies (ANA) and C-reactive protein (CRP), in patients affected by rheumatoid arthritis (RA), before and after infliximab treatment. Twenty-seven patients (five men and 22 women, mean age of 51.9 years, mean duration of disease 12.6 years) affected by RA, refractory to conventional DMARDs, were treated with infliximab, at the conventional dosage. Before starting infliximab and after 22 weeks, on the occasion of the fifth infusion, anti-CCP antibodies were tested by ELISA method. At the same time IgM RF, ANA and CRP level were measured. Before infliximab therapy, anti-CCP antibodies resulted positive in 23 patients (85.1%); the serum level did not change after infliximab treatment; only one case negative at baseline became slightly positive after treatment. Before and after therapy RF resulted positive in 22 cases (81.4%) and 21 cases (77.7%) respectively; comparing values at baseline with those after 22 weeks of treatment with infliximab, RF levels significantly decreased, as well as CRP values. In contrast to both anti-CCP antibodies, which remained stable, and to RF, which fell after infliximab, ANA were positive > or = 1: 160 in four cases at baseline and in 12 after treatment. The titre of anti-CCP antibodies did not significantly change after anti-TNFalpha blocker administration; instead the positivity of RF significantly decreased. As opposed to antinuclear and anti-dsDNA antibodies, which may appear or increase in titre during infliximab treatment, the typical autoantibodies detectable in RA show a different trend; in fact, anti-CCP antibodies remained stable and RF decreased.

Anti-citrullinated peptide antibodies may occur in patients with psoriatic arthritis

BACKGROUND

Anti-cyclic citrullinated peptide (anti-CCP) antibodies are considered highly specific markers of rheumatoid arthritis. Despite the high specificity of the test, anti-CCP antibodies have also been observed in psoriatic arthritis.

OBJECTIVE

To determine the frequency of anti-CCP antibodies in psoriatic arthritis and to describe the clinical characteristics of such patients.

METHODS

Serum samples from 192 patients with psoriatic arthritis were analysed for anti-CCP antibodies. A previously defined cut off point was applied at a specificity level of > or =98.5% (42 U/ml). Antibodies against pepA and pepB (two synthetic citrullinated peptides) were determined on samples containing anti-CCP antibodies by line immune assay. The swollen joint count and the numbers of affected joints (present or past) were recorded. Clinical features were noted and if available radiographs of hands and feet were scored for erosions. Rheumatoid factor was determined in all samples.

RESULTS

Anti-CCP antibodies were found in 15 patients (7.8%); 13 of 15 anti-CCP2 positive samples were also positive for anti-pepA or pepB antibodies. The prevalence of anti-CCP antibodies was higher than expected in view of the highly specific cut off applied in the test. Detailed analysis of the clinical and radiological features makes it improbable that the high prevalence of anti-CCP antibodies resulted solely from concomitant psoriasis and rheumatoid arthritis or from misclassification.

CONCLUSIONS

Anti-CCP antibodies may be present in patients with psoriatic arthritis. Although some of the present cohort could have had psoriasis with concomitant rheumatoid arthritis, a proportion at least had the typical characteristics of psoriatic arthritis as the primary diagnosis.

Predictive value of antibodies to cyclic citrullinated peptide in patients with very early inflammatory arthritis

OBJECTIVE

To study the prognostic value of antibodies to cyclic citrullinated peptide (anti-CCP) and rheumatoid factor (RF), alone and in combination, in patients with very early synovitis.

METHODS

A cross-sectional study was performed in patients with established inflammatory and noninflammatory disease to validate the assay in our unit and confirm previously reported sensitivities and specificities of anti-CCP antibodies. Subsequently, patients with synovitis of 3 months' duration were followed for 72 weeks and the ability of anti-CCP antibodies and RF to predict the development of rheumatoid arthritis (RA) and persistent inflammatory arthritis was assessed.

RESULTS

One hundred twenty-four patients were assessed in the initial cross-sectional study. Anti-CCP antibodies and RF were detected by ELISA in only 4% of patients with non-RA inflammatory disease and in no patient with noninflammatory disease. Ninety-six patients with very early synovitis were assessed longitudinally. In these patients with early arthritis, the combination of anti-CCP antibodies and RF had a specificity, positive predictive value (PPV), sensitivity, and negative predictive value (NPV) for a diagnosis of RA of 100%, 100%, 58%, and 88%, respectively. The specificity, PPV, sensitivity, and NPV of this antibody combination for the development of persistent disease-fulfilling classification criteria for RA were 97%, 86%, 63%, and 91%, respectively.

CONCLUSION

In patients with synovitis of 3 months' duration, a combination of anti-CCP antibodies and RF has a high specificity and PPV for the development of persistent RA. This autoantibody combination can be used to identify patients with disease destined to develop RA who may be appropriate for very early intervention.

A gene expression signature for recent onset rheumatoid arthritis in peripheral blood mononuclear cells

BACKGROUND

In previous studies the presence of a distinct gene expression pattern has been shown in peripheral blood cells from patients with autoimmune disease.

OBJECTIVE

To determine whether other specific signatures might be used to identify subsets of these autoimmune diseases and whether gene expression patterns in early disease might identify pathogenetic factors.

METHODS

Peripheral blood mononuclear cells were acquired from patients with rheumatoid arthritis (RA) and analysed by microarrays containing over 4300 named human genes. Patients with RA for <2 years were compared with subjects with longstanding RA (average duration 10 years) and with patients with other immune or autoimmune diagnoses.

RESULTS

Cluster analyses permitted separation of the patients with early RA (ERA) from those with longstanding disease. Comparison with other patient groups suggested that the ERA signature showed some overlap with that seen in the normal immune response to viral antigen as well as with a subset of patients with systemic lupus erythematosus.

CONCLUSIONS

The ERA signature may reflect, in part, a response to an unknown infectious agent. Furthermore, shared features with some lupus patients suggest that common aetiological factors and pathogenetic pathways may be involved in these two autoimmune disorders.

Interstitial lung disease in the patient who has connective tissue disease

Interstitial lung disease is a common complication of many of the connective tissue diseases. Because the prognosis, degree of reversibility, and optimal therapy differs for each disease presentation, a thorough knowledge of the pulmonary presentations of each connective tissue disease is important. Additionally, the challenge of finding the patient who has occult connective tissue disease in an interstitial lung disease clinic is discussed.

Diagnostic and prognostic values of anti glucose-6-phosphate isomerase antibodies in community-recruited patients with very early arthritis

The objective of this study was to determine the diagnostic and prognostic values of antiglucose-6-phosphate isomerase (GPI) antibodies in patients with very early arthritis. Anti-GPI antibodies were measured by ELISA using purified GPI from rabbit muscle in: (i) 383 sera from healthy blood donors (n = 120), well-established rheumatoid arthritis (RA) (n = 99) and non-RA differentiated arthritis (NRADA) (n = 164) patients; (ii) 195 sera obtained from community-recruited patients with very early inflammatory arthritis (VErA cohort) that were studied for 1 year and classified as having RA (n = 116), NRADA (n = 41), and undifferentiated arthritis (UA) (n = 38) after the follow-up period. The criterion for severity was the progression of radiographic damage. Prevalence of anti-GPI antibodies was significantly higher in well-established RA patients (45.4%) compared to healthy subjects (2.5%). Anti-GPI antibodies were also present in sera from NRADA: systemic lupus erythematosus 53%, polymyositis 45.4%, adult-onset Still's disease 44%, systemic sclerosis 42.8%, spondylarthropathies 25% and primary Sjögren's syndrome 5.8%. No significant association was found between the presence of anti-GPI antibodies and the 3 diagnostic groups from the VErA cohort. No correlation was observed between anti-GPI and autoantibodies usually associated with RA. Anti-GPI antibodies were not predictive of radiological progression in patients with very early arthritis. Thus, anti-GPI antibodies are not useful for discriminating RA from non-RA rheumatic diseases and do not constitute a predictive factor of structural damage.

Anti-CCP antibody test predicts the disease course during 3 years in early rheumatoid arthritis (the Swedish TIRA project)

OBJECTIVES

To evaluate the diagnostic sensitivity of antibodies to cyclic citrullinated peptide (CCP) in recent onset rheumatoid arthritis (RA) at diagnosis and 3 years later, and to evaluate anti-CCP antibody as a predictor of the disease course during 3 years.

METHODS

242 patients with recent onset (< or =1 year) RA were followed up regularly during 3 years after inclusion in the Swedish multicentre study "TIRA" 1996-98. Anti-CCP antibodies were analysed by an enzyme immunoassay (EIA). Rheumatoid factors (RFs) were analysed by latex agglutination and two isotype-specific (IgM and IgA) EIAs. Disease activity was assessed by plasma CRP, ESR, 28 joint disease activity score, and the physician's global assessment of disease activity. Functional ability was evaluated by the Health Assessment Questionnaire.

RESULTS

Overall, the diagnostic sensitivity of anti-CCP antibodies was 64% and the proportion of positive tests increased with the number of fulfilled classification criteria according to the American College of Rheumatology. The anti-CCP antibody results correlated with RF, but were better than RF as predictor of a more aggressive disease course. After 3 years 5/97 patients had changed anti-CCP status: 2 from negative to positive and 3 from positive to negative. The mean level of anti-CCP antibodies declined by 131 U/ml during the 3 year follow up (95% CI 34 to 228 U/ml).

CONCLUSION

The anti-CCP antibody assay has a similar diagnostic sensitivity to that of RF in early RA, but is better as a predictor of the disease course over 3 years. Although the mean serum level declines, anti-CCP antibody positivity remains essentially unaltered 3 years after diagnosis and start of antirheumatic treatment.

Diagnostic and clinical value of anti-cyclic citrullinated peptide antibodies compared with rheumatoid factor isotypes in rheumatoid arthritis

OBJECTIVE

To assess the additional diagnostic and clinical value of the second test generation of anti-cyclic citrullinated peptide antibodies (CCP2) compared with rheumatoid factor isotypes (IgG-RF, IgA-RF, IgM-RF) in patients with rheumatoid arthritis.

METHODS

This was a prospective study on 715 patients: rheumatoid arthritis (n = 295), degenerative or other inflammatory joint disease (n = 163), connective tissue disease or vasculitis (n = 103), and healthy controls (n = 154). Sera from each subject were tested for CCP2 and RF isotypes by enzyme linked immunosorbent assay (ELISA). Agreement with clinical indices such as disease activity, joint destruction, disease duration, and other laboratory tests was assessed. Sensitivity and specificity of the tests were evaluated taking the clinical diagnosis as the gold standard.

RESULTS

Highest sensitivity was found for IgM-RF (66.4%) and CCP (64.4%). Highest specificity was achieved by CCP (97.1%) and IgG-RF (91.0%). In rheumatoid patients with high disease activity or severe joint damage, CCP was more often present (81.4% and 83.6%) than all RF isotypes. Of special diagnostic value was the detection of positive CCP in 34.5% of all patients with rheumatoid arthritis when all measured RF isotypes (IgG-RF, IgA-RF, and IgM-RF) were negative.

CONCLUSIONS

As a screening method for rheumatoid arthritis the IgM-RF and the CCP assays are superior to other RF isotypes. Positivity in the highly specific CCP ELISA supports the diagnosis of rheumatoid arthritis. CCP proved to be a powerful diagnostic tool, especially in ambiguous cases or RF negative patients with rheumatoid arthritis.

Update on autoantibodies in rheumatoid arthritis

Detection of rheumatoid factor (RF) in the serum of patients with rheumatoid arthritis (RA) was one of the first indications of autoimmunity in RA. The role of RF in the diagnosis of RA has been well-documented, but it has suboptimal sensitivity and specificity. Although patients with RF-positive RA generally have more severe disease than those with RF-negative RA, RF is not a reliable predictor of disease severity in individual patients. Multiple other autoantibodies have been found in RA, with recent interest focused on those directed at cyclic citrullinated peptides. Panels of autoantibodies may ultimately prove useful in preclinical diagnosis and prediction of clinical course in patients with RA and other forms of arthritis, and provide insights into the pathogenesis of the disease.

Absence of antibodies to cyclic citrullinated peptide in sera of patients with hepatitis C virus infection and cryoglobulinemia

OBJECTIVE

To determine if antibodies to cyclic citrullinated peptide (anti-CCP) are found in chronic hepatitis C virus (HCV) infection.

METHODS

Rheumatoid factor (RF) and anti-CCP were measured in sera from 50 patients with HCV infection but without cryoglobulinemia, sera from 29 patients with mixed cryoglobulinemia (including 13 with rheumatic symptoms and 5 with arthritis), and sera from 20 normal blood donors. Anti-CCP was measured by second-generation enzyme-linked immunosorbent assay (ELISA).

RESULTS

No sera with elevated anti-CCP were found in patients with HCV infection without cryoglobulinemia, and in that population, the maximum anti-CCP was 10 units, well below the positive cutoff of 20 units. Positive findings on RF testing >13 IU/ml were present in 22 (44%) of the HCV patients, with RF >50 IU/ml in 8 (16%) and a maximum RF of 526 IU/ml. Of the cryoglobulinemia patients, 22 (76%) had positive results on tests for RF, including 18 (62%) with RF >50 IU/ml and a maximum RF of 5,540 IU/ml. Two (6.9%) of the cryoglobulinemia patients had borderline-positive findings on tests for anti-CCP (25 units and 37 units), which were false-positive results caused by nonspecific binding in the ELISA. No association between the RF and the anti-CCP concentrations was found.

CONCLUSION

Whereas RF was frequent in patients with HCV infection with and without cryoglobulinemia, anti-CCP was not observed in patients with uncomplicated HCV infection. Borderline-positive anti-CCP results were observed infrequently in patients with mixed cryoglobulinemia and were caused by nonspecific binding to plastic. Measurement of anti-CCP may help in diagnosing RA in patients with chronic HCV infection.

Development and evaluation of a patient self-report case-finding method for rheumatoid arthritis

OBJECTIVE

To describe the development and evaluation of a patient self-report case-finding method for rheumatoid arthritis (RA) not dependent on direct contact with the treating physicians.

METHODS

The American College of Rheumatology criteria for RA diagnosis were adapted for patient self-report using a questionnaire, and alternative scoring algorithms were evaluated to balance case-finding sensitivity and specificity. Positive rheumatoid factor tests were used to identify 1053 individuals in 2 large healthcare organizations; 440 agreed to receive study materials. Case-finding results were validated by medical record review (MRR) for a random sample of 90 patients. Three scoring algorithms were compared with MRR for likelihood of RA diagnosis. Cases not classifiable by algorithm were flagged and reviewed by 2 expert physicians for likelihood of RA diagnosis.

RESULTS

Pilot testing demonstrated that patients comprehended the questionnaire and were willing to answer the questions. Completed questionnaires were returned by 265 (60%) of the 440 patients contacted. Following expert physician review of 16 flagged cases in the 90-patient MRR subsample, the most accurate scoring algorithm demonstrated 80% sensitivity, 67% specificity, 74% accuracy, and 77% positive predictive value for detecting early RA.

CONCLUSION

The case-finding method represents a promising tool for identifying RA patients, with potential application in research and quality-assurance activities.

RELEVANCE

This case-finding method should be useful in research and quality-assurance efforts requiring identification of RA patients treated by all types of providers in healthcare organizations in which centralized laboratory data are available.

Relationship of psoriatic arthritis with the other spondyloarthropathies

PURPOSE OF REVIEW

The seronegative spondyloarthropathies are a group of disorders sharing common clinical features, the hallmark of which is sacroiliitis. Despite the 40 years since psoriatic arthritis was recognized, controversy still exists about which patients to include within this disease group and the relation of psoriatic arthritis with the other spondyloarthropathies.

RECENT FINDINGS

Early disease can present difficulties because it is inappropriate to use criteria developed on established cases in early arthritis, in which many cases may be initially undifferentiated. The taxonomy of juvenile spondyloarthropathy remains a contentious issue, and further modifications of the Durban criteria have been suggested. The predictive value of the European Spondyloarthropathy Study Group criteria for spondyloarthropathy varies with the prevalence of the disease in the population under consideration, as has been demonstrated in ambulatory practice in France and Spain. It appears that physicians differ in their interpretation of the individual features, particularly of such clinical items as asymmetry and predominantly lower limb involvement. The combination of dactylitis of a toe, heel pain, and oligoarthritis appears to be strongly suggestive of psoriatic arthritis. However, solitary heel pain can be problematic, and ultrasonographic entheseal erosion at the calcaneum has been shown equally in rheumatoid arthritis and psoriatic arthritis. MRI may be more sensitive and quantitatively discriminative in psoriatic arthritis. Spinal involvement in psoriatic arthritis can be asymptomatic, as in classical ankylosing spondylitis. Importantly, psoriatic spondylitis has been observed in the absence of sacroiliitis.

SUMMARY

Clinicians generally agree that psoriatic arthritis constitutes a discreet subset within the spondyloarthropathy group, but the demarcation continues to be the subject of clinical research. The matter is confounded by the lack of agreed classification criteria for psoriatic arthritis; although in both adult and juvenile disease criteria for spondyloarthropathy exist, the place of psoriatic arthritis within this larger group requires further definition.