Relapse incidence rates in 285 patient-years and hazard ratios after remission ADAMTS13 activity measurements within 1 year
| ADAMTS13 activity level, % . | Patient-years . | Relapses (patients), n . | Incidence of relapse per 100 patient-years (95% CI) . | Hazard ratio (95% CI) . | P . |
|---|---|---|---|---|---|
| <10 | 40.1 | 3 (3) | 7.48 (3.12-15.07) | 2.11 (0.54-8.25) | .285 |
| ≥10 | 244.9 | 7 (6) | 2.86 (0.56-8.55) | ||
| <15 | 54.6 | 5 (5) | 9.16 (4.22-17.29) | 4.01 (1.14-14.11) | .031 |
| ≥15 | 230.4 | 5 (4) | 2.17 (0.30-7.49) | ||
| <20 | 61.4 | 5 (5) | 8.14 (3.55-15.95) | 3.51 (1.00-12.36) | .051 |
| ≥20 | 223.5 | 5 (4) | 2.24 (0.32-7.60) | ||
| <30 | 68.1 | 5 (5) | 7.34 (3.03-14.88) | 3.24 (0.92-11.42) | .067 |
| ≥30 | 216.9 | 5 (4) | 2.31 (0.34-7.70) | ||
| <50 | 87.9 | 6 (6) | 6.83 (2.71-14.19) | 3.38 (0.93-12.34) | .065 |
| ≥50 | 197.1 | 4 (4) | 2.03 (0.25-7.27) | ||
| <60 | 103.1 | 8 (8) | 7.76 (3.30-15.44) | 6.95 (1.45-33.28) | .015 |
| ≥60 | 181.9 | 2 (2) | 1.10 (0.04-5.74) |
| ADAMTS13 activity level, % . | Patient-years . | Relapses (patients), n . | Incidence of relapse per 100 patient-years (95% CI) . | Hazard ratio (95% CI) . | P . |
|---|---|---|---|---|---|
| <10 | 40.1 | 3 (3) | 7.48 (3.12-15.07) | 2.11 (0.54-8.25) | .285 |
| ≥10 | 244.9 | 7 (6) | 2.86 (0.56-8.55) | ||
| <15 | 54.6 | 5 (5) | 9.16 (4.22-17.29) | 4.01 (1.14-14.11) | .031 |
| ≥15 | 230.4 | 5 (4) | 2.17 (0.30-7.49) | ||
| <20 | 61.4 | 5 (5) | 8.14 (3.55-15.95) | 3.51 (1.00-12.36) | .051 |
| ≥20 | 223.5 | 5 (4) | 2.24 (0.32-7.60) | ||
| <30 | 68.1 | 5 (5) | 7.34 (3.03-14.88) | 3.24 (0.92-11.42) | .067 |
| ≥30 | 216.9 | 5 (4) | 2.31 (0.34-7.70) | ||
| <50 | 87.9 | 6 (6) | 6.83 (2.71-14.19) | 3.38 (0.93-12.34) | .065 |
| ≥50 | 197.1 | 4 (4) | 2.03 (0.25-7.27) | ||
| <60 | 103.1 | 8 (8) | 7.76 (3.30-15.44) | 6.95 (1.45-33.28) | .015 |
| ≥60 | 181.9 | 2 (2) | 1.10 (0.04-5.74) |
Only the 10 relapses that were preceded by an ADAMTS13 measurement within 12 months were included in this analysis. These 10 relapses occurred in 9 patients. In 1 patient who had 2 relapses, 1 relapse occurred after ADAMTS13 activity of 34% and the other relapse occurred after ADAMTS13 activity of 64%; therefore, he is included in both rows for the <50%/≥50% analysis and the <60%/≥60% analysis, creating the appearance of 10 patients. Hazard ratios were calculated using a modified Cox regression analysis,9 a time-to-event analysis that allows TTP relapse as a recurring event related to the time-varying measurement of ADAMTS13 activity during remission. This model also accounts for the competing events of death unrelated to an acute TTP episode. Due to ADAMTS13 activity being treated as a time-varying covariate, the assumption of proportional hazards is not relevant because the modification of the Cox regression model uses the partial likelihood estimation method.9