Table 4. Percentage of Time in the Therapeutic Range (PTTR) Through Week 4 of Therapya.
| Genotype-Guided Warfarin Dosing | Clinically Guided Warfarin Dosing | Mean Difference (95% CI), % |
P Value |
P Value for Interaction |
|||
|---|---|---|---|---|---|---|---|
| No. of Patients |
Mean PTTR (95% CI), % |
No. of Patients |
Mean PTTR (95% CI), % |
||||
| All patients | 803 | 54.7 (53.0 to 56.4) | 785 | 51.3 (49.6 to 53.0) | 3.4 (1.1 to 5.8) | .004 | |
| Per-protocol analysis | 784 | 55.1 (53.4 to 56.8) | 761 | 51.9 (50.2 to 53.6) | 3.3 (0.9 to 5.7) | .006 | |
| High-risk subgroupb | 321 | 55.3 (52.7 to 57.9) | 333 | 48.4 (45.9 to 50.9) | 7.0 (3.4 to 10.6) | <.001 | |
| INR target | |||||||
| 1.8 (range, 1.5-2.1) | 404 | 53.3 (50.9 to 55.7) | 396 | 52.1 (49.7 to 54.5) | 1.1 (–2.2 to 4.5) | .51 | .053 |
| 2.5 (range, 2.0-3.0) | 399 | 56.2 (53.9 to 58.5) | 389 | 50.4 (48.1 to 52.7) | 5.8 (2.5 to 9.1) | .001 | |
| Absolute difference between algorithms in predicted warfarin dose | |||||||
| ≥1.0 mg/d (high-risk group) | 321 | 55.3 (52.7 to 57.9) | 333 | 48.4 (45.9 to 50.9) | 7.0 (3.4 to 10.6) | <.001 | .006 |
| <1.0 mg/d | 482 | 54.3 (52.1 to 56.5) | 452 | 53.4 (51.2 to 55.6) | 0.9 (–2.2 to 4.0) | .57 | |
| Race | |||||||
| Black | 52 | 50.9 (44.8 to 57.0) | 50 | 50.7 (44.1 to 57.4) | 0.2 (–8.9 to 9.4) | .96 | .48 |
| Other races | 751 | 55.0 (53.3 to 56.7) | 735 | 51.3 (49.6 to 53.0) | 3.7 (1.2 to 6.1) | .003 | |
| Type of arthroplasty | |||||||
| Knee | 599 | 54.4 (52.4 to 56.4) | 586 | 50.9 (49.0 to 52.8) | 3.6 (0.8 to 6.3) | .01 | .86 |
| Hip | 204 | 55.5 (52.4 to 58.6) | 199 | 52.4 (48.9 to 55.9) | 3.1 (–1.6 to 7.8) | .19 | |
| Analysis by 2-wk intervals | |||||||
| From day 4-14 | 803 | 48.5 (26.1 to 67.3)c | 785 | 42.9 (22.9 to 62.0)c | 5.7 (2.2 to 9.2) | .005 | |
| From day 15-28 | 790 | 65.0 (31.8 to 100.0)c | 767 | 61.1 (29.1 to 100.0)c | 3.9 (–1.8 to 10.0) | .13 | |
Abbreviation: INR, international normalized ratio.
a
There were 1588 patients who had an INR measured on or after day 4 and were included in PTTR calculations (those without INR measurements were excluded from the PTTR calculations in this Table).
b
Consists of patients whose clinically guided vs genotype-guided doses of warfarin differed by 1.0 mg/d or greater (according to baseline genotype and clinical algorithms).
c
Data expressed as median (interquartile range) because the PTTR was not normally distributed.