Questions included in study part I: questions selected by monovariate and multivariate analysis
| Questions | Sensitivity (%) | 95% CI (%) | Specificity (%) | 95% CI (%) |
|---|---|---|---|---|
| Univariate analysis | ||||
| 1. Do you remember one or more episodes of small red spots on your skin particularly involving the lower limbs? | 81.9 | 76.3 to 87.4 | 68.3 | 62.8 to 73.7 |
| 2. Had you ever had red spots in your lower extremities associated with itching or pain? | 60.1 | 53.1 to 67.1 | 80.6 | 76.0 to 85.2 |
| 3. Have you ever noticed small red dots on your legs and/or feet that don't disappear when squeezed and take a long time to fade away? | 67.0 | 60.3 to 73.8 | 83.4 | 79.1 to 87.8 |
| 4. Had you ever had red spots in your lower extremities which leave a brownish colour after their disappearance? | 69.2 | 62.5 to 75.8 | 85.2 | 81.1 to 89.3 |
| 5. Do you remember episodes of small red spots or macules on your skin, particularly involving the lower limbs, arising in a few hours (eg, from one evening to the following morning) and usually lasting from a few days to 1–2 weeks? | 75.0 | 66.8 to 81.2 | 82.4 | 77.9 to 86.8 |
| 10. Have you ever had bad or non-healing skin ulcers in your legs? | 20.3 | 14.6 to 26.2 | 89.1 | 85.4 to 92.7 |
| 12. Have you ever felt a burning sensation in your lower extremities for more than 1 month? | 36.2 | 29.6 to 43.5 | 78.9 | 74.0 to 83.6 |
| 13. Do you have a change of feeling (painful or changed sensation) and/or palsy of muscles in your extremities? | 51.9 | 44.4 to 58.8 | 63.6 | 58.0 to 69.2 |
| 14. Do you ever feel pins and needles in your legs or arms? | 64.9 | 58.2 to 71.9 | 57.0 | 51.1 to 62.7 |
| 17. Did a doctor ever tell you that you have viral hepatitis? | 81.4 | 76.1 to 87.3 | 84.5 | 80.2 to 88.7 |
| Multivariate analysis | ||||
| Question 1 ∪ Question 17 | 96.8 | 94.3 to 99.3 | 57.4 | 51.6 to 63.2 |
| Question 1 ∪ Question 4 | 83.5 | 78.2 to 88.8 | 67.6 | 61.2 to 73.1 |
| Question 4 ∪ Question 17 | 96.3 | 93.5 to 99.0 | 73.2 | 68.1 to 78.4 |
| Question 1 ∪ Question 4 ∪ Question 17 | 97.3 | 95.0 to 99.6 | 57.4 | 51.6 to 63.2 |
| Question 1 ∩ Question 17 | 66.5 | 59.7 to 73.3 | 95.4 | 93.0 to 97.9 |
| Question 1 ∩ Question 4 | 67.6 | 60.8 to 74.3 | 85.9 | 81.8 to 90.0 |
| Question 4 ∩ Question 17 | 54.3 | 47.1 to 61.4 | 96.5 | 94.3 to 98.6 |
| Question 1 ∩ Question 4 ∩ Question 17 | 53.2 | 46.0 to 60.4 | 97.2 | 95.2 to 99.1 |
| Positive response for at least any two out of the three questions 1, 4, 17 | 81.9 | 76.4 to 87.4 | 83.5 | 79.1 to 87.8 |