Table 3.
Sensitivity, specificity, positive predictive value (PPV), and negative predictive value (NPV) of assays for a diagnosis of C1 inhibitor deficiency
| C4 | C1 inhibitor (immunochemical) | Functional C1 inhibitor | C4 and functional C1 inhibitor | |
| Using all samples | ||||
| Sensitivity | 70% | 65% | 97% | 70% |
| Specificity | 93% | 94% | 81% | 98% |
| PPV | 56% | 56% | 36% | 79% |
| NPV | 96% | 96% | 99% | 96% |
| Using first samples in study period | ||||
| Sensitivity | 65% | 65% | 96% | 65% |
| Specificity | 94% | 94% | 84% | 99% |
| PPV | 23% | 22% | 14% | 58% |
| NPV | 99% | 99% | 100% | 99% |
| Using untreated C1inhD v first sample from non-C1inhD | ||||
| Sensitivity | 100% | 85% | 100% | 100% |
| Specificity | 94% | 94% | 84% | 99% |
| PPV | 29% | 25% | 13% | 65% |
| NPV | 100% | 99% | 100% | 100% |
The PPV associated with the immunochemical C1 inhibitor measurement incorporates type 2 hereditary angioedema. The C1 inhibitor values will be normal or raised despite functional deficiency.
C1inhD, C1 inhibitor deficiency.