Table 2.
Summary of clinical performance characteristics of the assays used in this study.
| CCP2 IgG ELISA | CCP3 IgG ELISA | CCP3 IgG CIA | RF IgM ELISA | RF IgM CIA | RF IgA ELISA | RF IgA CIA | RF IgG ELISA | |
|---|---|---|---|---|---|---|---|---|
| Cutoff | 25 U/mL | 20 U | 20 CU | 6 U | 10,344 RLU | 6 U | 7,425 RLU | 6 U |
| # Positive samples/total # samples (%) | 778/1,655 (47.0) | 609/1,655 (36.8) | 604/1,655 (36.5) | 698/1,655 (42.2) | 745/1,655 (45.0) | 682/1,655 (41.2) | 416/1,655 (25.1) | 445/1,655 (26.9) |
| # Positive RA samples/total # RA samples (%) | 688/968 (71.1) | 598/968 (61.8) | 594/968 (61.4) | 611/698 (63.1) | 650/968 (67.1) | 530/968 (54.8) | 395/968 (40.8) | 345/968 (35.6) |
| # Positive samples/total # axSpA samples (%) | 59/450 (13.1) | 8/450 (1.8) | 6/450 (1.3) | 56/450 (12.4) | 60/450 (13.3) | 103/450 (22.9) | 14/450 (3.1) | 68/450 (15.1) |
| # Positive PA samples/total # PsA samples (%) | 31/237 (13.1) | 3/237 (1.3) | 4/237 (1.7) | 31/237 (13.1) | 35/237 (14.8) | 49/237 (20.7) | 7/237 (3.0) | 32/237 (13.5) |
| Sensitivity (%) | 71.1 | 61.8 | 61.4 | 63.1 | 67.1 | 54.8 | 40.8 | 35.6 |
| Specificity (%) | 86.9 | 98.4 | 98.5 | 87.3 | 86.2 | 77.9 | 96.9 | 85.4 |
| OR (95% CI) | 16.3 (12.5–21.2) | 99.3 (54.4–181.2) | 107.5 (57.4–201.5) | 11.8 (9.1–15.3) | 12.7 (9.9–16.4) | 4.3 (3.4–5.3) | 21.9 (13.9–34.3) | 3.3 (2.5–4.2) |
| AUC (95% CI) | 0.82 (0.80–0.84) | 0.83 (0.81–0.85) | 0.82 (0.81–0.84) | 0.79 (0.77–0.81) | 0.82 (0.80–0.84) | 0.70 (0.67–0.72) | 0.79 (0.77–0.81) | 0.61 (0.59–0.64) |
| Cutoff for 95% specificity | 53.0 | 8.3 | 6.6 | 14.6 | 24,767 | 14.2 | 5,252 | 8.3 |
| Sensitivity at 95% specificity | 61.3 | 68.1 | 66.1 | 50.2 | 55.0 | 39.7 | 48.1 | 27.6 |
| OR at 95% specificity (95% CI) | 29.7 (20.7–42.7) | 39.9 (27.7–57.5) | 36.5 (25.4–52.6) | 18.8 (13.1–27.0) | 22.1 (15.4–31.5) | 12.6 (8.7–18.2) | 17.3 (12.1–24.8) | 7.2 (5.0–10.4) |
| Cutoff 3× ULN | 75 | 60 | 60 | 18 | 31,032 | 18 | 22,275 | 18 |
| Sensitivity at 3× ULN (%) | 59.0 | 51.2 | 53.0 | 47.5 | 52.7 | 35.7 | 21.8 | 16.0 |
| OR at 3× ULN (95% CI) | 45.6 (29.1–71.5) | 102.1 (48.8–213.7) | 192.5 (74.1–500.2) | 20.5 (13.9–30.4) | 28.3 (18.8–42.6) | 14.7 (9.7–22.4) | 38.0 (16.0–90.4) | 26.0 (10.9–62.1) |
| p-Value | 7.31e−29 | 1.36e−105 | 2.87e−25 | 8.09e−58 | 1.23e−48 | 4.44e−36 | 2.53e−13 | 2.29e−15 |
| FDR | True | True | True | True | True | True | True | True |
CCP, cyclic citrullinated peptide; RF, rheumatoid factor; CIA, chemiluminescent immunoassay; RUO, research use only; CU, chemiluminescent units; RLU, relative light units; OR, odds ratio; AUC, area under the curve; ULN, upper limit of normal; FDR, false discovery rate; RA, rheumatoid arthritis; axSpA, axial spondyloarthritis; ELISA, enzyme-linked immunosorbent assay.