Table 1.
The performance of a commercial line blot compared with immunoprecipitation
| Autoantibody (n) | Line blot result | Number of samples with index MSAA as false positivea | Specificity | Sensitivity | Cohen’s κ | |
|---|---|---|---|---|---|---|
| False negative | True positive | |||||
| Mi2a (25) | 9 | 16 | 0 | 1 | 0.64 | 0.77 |
| Mi2b (25) | 17 | 8 | 7 | 0.98 | 0.32 | 0.37 |
| Mi2a or Mi2b (25) | 7 | 18 | 7 | 0.98 | 0.72 | 0.70 |
| TIF1γ (25) | 10 | 15 | 2 | 0.99 | 0.6 | 0.70 |
| MDA5 (25) | 3 | 22 | 4 | 0.99 | 0.88 | 0.85 |
| NXP2 (25) | 4 | 21 | 0 | 1 | 0.84 | 0.91 |
| SAE (25) | 1 | 24 | 2 | 0.99 | 0.96 | 0.94 |
| Ku (24) | 0 | 24 | 12 | 0.97 | 0.97 | 0.78 |
| PM/Scl-75 (25) | 11 | 14 | 10 | 0.98 | 0.56 | 0.56 |
| PM/Scl- 100 (25) | 5 | 20 | 3 | 0.99 | 0.8 | 0.82 |
| PM/Scl-75 or PM/Scl-100 (25) | 4 | 21 | 13 | 96.2 | 0.84 | 0.69 |
| Jo-1 (25) | 3 | 22 | 4 | 0.98 | 0.82 | 0.85 |
| SRP (25) | 2 | 23 | 6 | 0.98 | 0.92 | 0.84 |
| PL-7 (21) | 5 | 16 | 5 | 0.99 | 0.64 | 0.75 |
| PL-12 (20) | 2 | 18 | 5 | 0.99 | 0.9 | 0.83 |
| EJ (10) | 4 | 6 | 0 | 1 | 0.6 | 0.76 |
| OJ (14) | 14 | 0 | 1 | 1 | 0 | 0 |
| Zo (9) | – | – | – | – | – | – |
| KS (3) | – | – | – | – | – | – |
| Ha (1) | – | – | – | – | – | – |
| HMGCR (25) | – | – | – | – | – | – |
| Healthy controls (68) | 0 | 0 | 11b | – | – | – |
| Total (395) | 54 | 199c | 54d | 0.62 | 0.78 | 0.41 |
The sensitivity, specificity and Cohen’s κ coefficient for each assay are shown. Tests with κ < 0.8 are highlighted in bold.
a
Some samples contained more than one false positive result. In total, 54 samples contained at least one false positive result.
b
One sample was positive for anti-Ro52. The 11 listed were positive for myositis-specific autoantibodies. Anti-Ro52 were excluded from specificity calculations, as immunoprecipitation is unable to detect this autoantibody, which can be found in healthy individuals.
c
Samples that contained a true positive result and no false positive result.
d
Number of samples analysed containing at least one false positive result.