Frequency of HIT, thrombosis (HIT, non-HIT associated, total), and HIT antibodies in before-after prospective cohort study comparing UFH and LMWH after orthopedic surgery
. | UFH, n = 231 (%) . | LMWH, n = 271 (%) . | P . |
|---|---|---|---|
| Patients with HIT* | 12 (5.2) | 0 (0) | < .001 |
| All symptomatic thrombotic events, HIT and non-HIT associated | 9 (3.9) | 2 (0.7) | .028 |
| All symptomatic thrombotic events before or on day 4† | 1 (0.4) | 1 (0.4) | .910 |
| All symptomatic non-HIT-associated thrombotic events after day 4‡ | 2 (0.9) | 1 (0.4) | .597 |
| All symptomatic HIT-associated thrombotic events after day 4 (HIT)§ | 6 (2.6) | 0 (0) | .009 |
| HIT antibody status at day 16/platelet activation assay | 25/202 (12.4) | 13/238 (5.5) | .010 |
| HIT antibody status at day 16/immunoassay | 46/196 (23.5) | 19/228 (8.3) | < .001 |
. | UFH, n = 231 (%) . | LMWH, n = 271 (%) . | P . |
|---|---|---|---|
| Patients with HIT* | 12 (5.2) | 0 (0) | < .001 |
| All symptomatic thrombotic events, HIT and non-HIT associated | 9 (3.9) | 2 (0.7) | .028 |
| All symptomatic thrombotic events before or on day 4† | 1 (0.4) | 1 (0.4) | .910 |
| All symptomatic non-HIT-associated thrombotic events after day 4‡ | 2 (0.9) | 1 (0.4) | .597 |
| All symptomatic HIT-associated thrombotic events after day 4 (HIT)§ | 6 (2.6) | 0 (0) | .009 |
| HIT antibody status at day 16/platelet activation assay | 25/202 (12.4) | 13/238 (5.5) | .010 |
| HIT antibody status at day 16/immunoassay | 46/196 (23.5) | 19/228 (8.3) | < .001 |
The 12 patients who met the a priori definition for HIT included 6 with platelet count fall (> 30%) alone, 3 with platelet fall (> 30%) plus symptomatic thrombosis, and 3 with symptomatic thrombosis alone; all HIT-associated symptomatic thrombi occurred after day 4. (Six of the 12 HIT patients had a platelet count fall more than 50%, 2 with thrombosis.)
One UFH-treated patient developed pulmonary embolism (day 1), and one LMWH-treated patient developed cardiac shock (day 2).
Two UFH-treated patients developed pulmonary embolism (both day 10), and 1 LMWH-treated patient developed acute coronary syndrome (day 7).
Four UFH-treated patients developed deep vein thromboses (DVTs; days 8, 8, 10, and 16), and 2 developed pulmonary embolism (days 7 and 15).