Test characteristics of immunofluorescence and ELISA tests in 856 consecutive patients with possible ANCA-associated conditions

OBJECTIVE

To examine the test characteristics of immunofluorescence (IF) and enzyme-linked immunosorbent assays (ELISA) in a consecutive series of patients under evaluation for anti-neutrophil cytoplasmic antibody (ANCA)-associated vasculitis (AAV).

METHODS

Using stored sera, we performed a cross-sectional study on 856 consecutive patients tested prospectively for ANCA by IF, Based on guidelines from the 1994 Chapel Hill Consensus Conference (CHCC), we determined each patient's underlying diagnosis by a medical records review without regard to their ANCA status (the CHCC guidelines do not require ANCA as a prerequisite for diagnosis). We grouped patients with forms of vasculitis commonly associated with ANCA into one of 4 types of AAV: Wegener's granulomatosis (n = 45), microscopic polyangiitis (n = 12), Churg-Strauss syndrome (n = 4), and pauci-immune glomerulonephritis (n = 8). We also classified patients without clinical evidence of AAV (92% of all patients tested) into 5 predefined categories of disease (including "other") and an additional category for no identifiable disease. In a blinded fashion, we then performed ELISAs on the stored serum for antibodies to proteinase-3 (PR3) and myeloperoxidase (MPO) and calculated the test characteristics for both ANCA assay techniques.

RESULTS

Sixty-nine of the 856 patients (8.1%) had clinical diagnoses of AAV based on CHCC guidelines. The positive predictive value (PPV) of ELISA for AAV was superior to that of IF, 83% versus 45%. For patients with both positive IF tests and positive ELISA tests, the PPV increased to 88%. Both IF and ELISA had high negative predictive values (97% and 96%, respectively). Positive ELISA tests were associated with higher likelihood ratios (LR) than IF (54.2 [95% CI = 26.3, 111.5] versus 9.4 [95% CI = 6.9, 12.7]). The LR of both a positive IF and a positive ELISA was 82.1 (95% CI = 33.3, 202.5).

CONCLUSIONS

Compared with IF, an ELISA test fo ANCA was associated with a substantially higher PPV and LR for AAV. This fact, combined with the greater sensitivity of IF, suggests that an effective testing strategy is to perform ELISA tests only on samples that are positive for ANCA by IF.

Test characteristics of immunofluorescence and ELISA tests in 856 consecutive patients with possible ANCA-associated conditions

OBJECTIVE

To examine the test characteristics of immunofluorescence (IF) and enzyme-linked immunosorbent assays (ELISA) in a consecutive series of patients under evaluation for anti-neutrophil cytoplasmic antibody (ANCA)-associated vasculitis (AAV).

METHODS

Using stored sera, we performed a cross-sectional study on 856 consecutive patients tested prospectively for ANCA by IF, Based on guidelines from the 1994 Chapel Hill Consensus Conference (CHCC), we determined each patient's underlying diagnosis by a medical records review without regard to their ANCA status (the CHCC guidelines do not require ANCA as a prerequisite for diagnosis). We grouped patients with forms of vasculitis commonly associated with ANCA into one of 4 types of AAV: Wegener's granulomatosis (n = 45), microscopic polyangiitis (n = 12), Churg-Strauss syndrome (n = 4), and pauci-immune glomerulonephritis (n = 8). We also classified patients without clinical evidence of AAV (92% of all patients tested) into 5 predefined categories of disease (including "other") and an additional category for no identifiable disease. In a blinded fashion, we then performed ELISAs on the stored serum for antibodies to proteinase-3 (PR3) and myeloperoxidase (MPO) and calculated the test characteristics for both ANCA assay techniques.

RESULTS

Sixty-nine of the 856 patients (8.1%) had clinical diagnoses of AAV based on CHCC guidelines. The positive predictive value (PPV) of ELISA for AAV was superior to that of IF, 83% versus 45%. For patients with both positive IF tests and positive ELISA tests, the PPV increased to 88%. Both IF and ELISA had high negative predictive values (97% and 96%, respectively). Positive ELISA tests were associated with higher likelihood ratios (LR) than IF (54.2 [95% CI = 26.3, 111.5] versus 9.4 [95% CI = 6.9, 12.7]). The LR of both a positive IF and a positive ELISA was 82.1 (95% CI = 33.3, 202.5).

CONCLUSIONS

Compared with IF, an ELISA test fo ANCA was associated with a substantially higher PPV and LR for AAV. This fact, combined with the greater sensitivity of IF, suggests that an effective testing strategy is to perform ELISA tests only on samples that are positive for ANCA by IF.

Etanercept combined with conventional treatment in Wegener's granulomatosis: a six-month open-label trial to evaluate safety

OBJECTIVE

To evaluate the safety of etanercept (Enbrel) in patients receiving conventional treatment for Wegener's granulomatosis (WG).

METHODS

We performed a 6-month open-label trial of etanercept (25 mg subcutaneously twice weekly) which was added to standard therapies for WG (glucocorticoids, methotrexate, cyclophosphamide, azathioprine, cyclosporine) and prescribed according to disease severity. Evaluations of clinical response were determined by the Birmingham Vasculitis Activity Score for WG (BVAS/WG) in 20 patients with persistently active disease or with new flares of previously established WG. Fourteen of the 20 patients (70%) had etanercept added as the only new therapeutic variable.

RESULTS

Injection site reactions (ISRs) were the most common adverse event related to etanercept (8 episodes in 5 patients [25%]; < 1% of all injections). All ISRs were mild. Two patients had a combined total of 5 hospitalizations (1 patient had 4), but no hospitalizations were attributable solely to etanercept-related adverse events. One patient with severe subglottic stenosis developed pneumococcal tracheobronchitis and subsequently had a localized Herpes zoster infection. Nineteen patients (95%) were still taking etanercept at 6 months, the single exception being a patient who developed progression of orbital (retro-bulbar) disease at 4 months. There were no deaths. The mean BVAS/WG at entry was 3.6 (range 1-8), which decreased at 6 months to 0.6 (P < 0.001, 95% confidence interval [95% CI] -4.0 to -2.1). Among the 14 patients in whom etanercept was the only new treatment variable, the mean daily prednisone dose decreased from 12.9 mg at entry to 6.4 mg at 6 months. This comparison did not achieve statistical significance (difference -6.5; P = 0.19, 95% CI -16.6 to +3.6). Sixteen of the patients (80%) achieved BVAS/WG scores of 0 at some point. However, intermittently active disease was observed in 15 patients (75%).

CONCLUSION

In this open-label trial, etanercept used in combination with standard treatments was well-tolerated in patients with WG. Adverse events were few. BVAS/WG scores improved at 6 months, but intermittently active WG (occasionally severe) was common. A randomized, double-masked trial to assess the efficacy of etanercept in WG has begun.

A disease-specific activity index for Wegener's granulomatosis: modification of the Birmingham Vasculitis Activity Score. International Network for the Study of the Systemic Vasculitides (INSSYS)

OBJECTIVE

To refine and validate the Birmingham Vasculitis Activity Score (BVAS) as a disease-specific activity index for Wegener's granulomatosis (WG).

METHODS

Sixteen members of the International Network for the Study of the Systemic Vasculitides (INSSYS) revised the BVAS, with 3 goals: to reduce the redundancy of some component items, to enhance its ability to capture important disease manifestations specific to WG, and to streamline the instrument for use in clinical research. We defined the items and weighted them empirically as either minor (e.g., nasal crusting = 1 point) or major (e.g., alveolar hemorrhage = 3 points). We then validated the new, disease-specific BVAS/WG in 2 simulation exercises and a clinical case series that involved 117 patients with WG.

RESULTS

We removed 38 items from the original BVAS, revised 9 items, and added 7 new items. Correlations between the scores on the BVAS/WG and the physician's global assessment (PGA) of disease activity were high, even when patients in remission were excluded. In the clinical case series, Spearman's rank correlation coefficient between the BVAS/WG and the PGA was r = 0.81 (95% confidence interval 0.73-0.87). The interobserver reliability using intraclass (within-case) correlation coefficients in the 2 simulation exercises was r = 0.93 for the BVAS/WG and r = 0.88 for the PGA in the first and r = 0.91 for the BVAS/WG and r = 0.88 for the PGA in the second. There was no significant observer effect in the scoring of the BVAS/WG or the PGA. The discriminant validity of the BVAS/WG was good: r = 0.73 (95% confidence interval 0.43-0.83).

CONCLUSION

The BVAS/WG is a valid, disease-specific activity index for WG. Tested in simulation exercises and in actual patients, the BVAS/WG correlates well with the PGA, is sensitive to change, and has good inter- and intraobserver reliability. The INSSYS will use the BVAS/WG to assess the primary outcome in a phase II/III trial of etanercept in WG.