Table 3.
Logistic regression model comparing the ability of baseline CRP and baseline biomarker levels for the prediction of clinical improvement at week 14
| Model (true/predicted)* | ASAS 20 response | BASDAI 50 response | ≥2 Unit improvement in BASFI score | ||||||
|---|---|---|---|---|---|---|---|---|---|
| Baseline CRP only* | NR | R | Accuracy† | NR | R | Accuracy† | NR | R | Accuracy† |
| Non-responder | 14 | 11 | Specificity: 56% | 20 | 11 | Specificity: 65% | 21 | 10 | Specificity: 68% |
| Responder | 11 | 39 | Sensitivity: 78% | 24 | 21 | Sensitivity: 47% | 18 | 27 | Sensitivity: 60% |
| Predictive value | NPV 56% | PPV 78% | NPV 45% | PPV 66% | NPV 54% | PPV 73% | |||
| Baseline biomarker* | NR | R | Accuracy* | NR | R | Accuracy* | N | R | Accuracy* |
| Non-responder | 17 | 8 | Specificity: 65% | 26 | 18 | Specificity: 59% | 17 | 22 | Specificity: 61% |
| Responder | 5 | 45 | Sensitivity: 90% | 3 | 29 | Sensitivity: 91% | 3 | 34 | Sensitivity: 85% |
| Predictive value | NPV 77% | PPV 85% | NPV 90% | PPV 65% | NPV 85% | PPV 61% | |||
| Predictors‡ | Weight | OR | p value | Weight | OR | p value | Weight | OR | p value |
| Immunoglobulin M | – | – | – | 1.24 | 3.46 | 0.006 | – | – | – |
| Insulin | -0.50 | 0.61 | 0.007 | – | – | – | – | – | – |
| Leptin | – | – | – | -0.69 | 0.50 | 0.0004 | – | – | – |
| N-terminal propeptide of type I collagen | 1.98 | 7.24 | 0.001 | – | – | – | 1.41 | 4.10 | 0.007 |
| Tissue inhibitor of metalloproteinases 1 | – | – | – | – | – | – | 3.35 | 28.50 | 0.002 |
| Vascular endothelial growth factor | – | – | – | 0.79 | 2.20 | 0.026 | – | – | – |
All biomarker values were log2-transformed before inclusion in the models. Both models are based on 76 patients.
Model accuracy (sensitivity, specificity, NPV, PPV) was estimated using cross-validation.
Weights are the coefficients in the logistic regression model. OR are the exponential of the weights. Multivariate p values are based on the inclusion of all terms in the model.
ASAS 20, at least 20% improvement in Assessment in SpondyloArthritis international Society response criteria; BASDAI 50, ≥50% improvement in the Bath ankylosing spondylitis disease activity index; BASFI, Bath ankylosing spondylitis functional index; CRP, C-reactive protein; NPV, negative predictive value; NR, non-responders; PPV, positive predictive value; R, responders.