Relationship of the patient population and type of heparin on frequency of HIT-IgG antibody formation and risk for developing HIT
| Patient population, type of heparin (mean ± SD duration of heparin [d]) . | Frequency of HIT antibody positivity (95% CI) . | Frequency of HIT (95% CI)† . | Frequency of HIT–IgG-positive patients with HIT (95% CI) . | ||
|---|---|---|---|---|---|
| Activation assay* . | Antigen assay* . | Activation assay‡ . | Antigen assay‡ . | ||
| Cardiac-UFH, n = 100 | 20/100 | 50/100 | 1/100 | 1/20 | 1/50 |
| (5.1 ± 2.2) | 20.0% (12.7-29.2) | 50.0% (39.8-60.2) | 1.0% (0.03-5.5) | 5.0% (0.1-24.9) | 2.0% (0.12-10.7) |
| Orthopedic-UFH, n = 205 | 19/205 | 29/205 | 10/205 | 10/19 | 10/29 |
| (9.2 ± 2.2) | 9.3% (5.7-14.1) | 14.1% (9.7-19.7) | 4.9% (2.4-8.8) | 52.6% (28.9-75.6) | 34.5% (17.9-54.3) |
| Orthopedic-LMWH, n = 439 | 14/439 | 33/439 | 4/439 | 4/14 | 4/33 |
| (9.5 ± 3.0) | 3.2% (1.8-5.3) | 7.5% (5.2-10.4) | 0.9% (0.3-2.3) | 28.6% (8.4-58.1) | 12.1% (3.4-28.2) |
| Pvalues | |||||
| Cardiac vs Orthopedic | .01 | <.001 | .71 | .01 | .004 |
| UFH vs LMWH | .002 | .009 | .015 | .19 | .048 |
| Patient population, type of heparin (mean ± SD duration of heparin [d]) . | Frequency of HIT antibody positivity (95% CI) . | Frequency of HIT (95% CI)† . | Frequency of HIT–IgG-positive patients with HIT (95% CI) . | ||
|---|---|---|---|---|---|
| Activation assay* . | Antigen assay* . | Activation assay‡ . | Antigen assay‡ . | ||
| Cardiac-UFH, n = 100 | 20/100 | 50/100 | 1/100 | 1/20 | 1/50 |
| (5.1 ± 2.2) | 20.0% (12.7-29.2) | 50.0% (39.8-60.2) | 1.0% (0.03-5.5) | 5.0% (0.1-24.9) | 2.0% (0.12-10.7) |
| Orthopedic-UFH, n = 205 | 19/205 | 29/205 | 10/205 | 10/19 | 10/29 |
| (9.2 ± 2.2) | 9.3% (5.7-14.1) | 14.1% (9.7-19.7) | 4.9% (2.4-8.8) | 52.6% (28.9-75.6) | 34.5% (17.9-54.3) |
| Orthopedic-LMWH, n = 439 | 14/439 | 33/439 | 4/439 | 4/14 | 4/33 |
| (9.5 ± 3.0) | 3.2% (1.8-5.3) | 7.5% (5.2-10.4) | 0.9% (0.3-2.3) | 28.6% (8.4-58.1) | 12.1% (3.4-28.2) |
| Pvalues | |||||
| Cardiac vs Orthopedic | .01 | <.001 | .71 | .01 | .004 |
| UFH vs LMWH | .002 | .009 | .015 | .19 | .048 |
The 15 patients with clinical HIT all tested positive by antigen and activation assays. Logistic regression analysis was used to compare 2 variables, patient population (cardiac compared with orthopedic patients) and heparin preparation (UFH compared with LMWH), with respect to 2 outcome measures—the frequency of patients testing positive for HIT-IgG antibodies and the proportion of antibody-positive patients in whom thrombocytopenia developed. Among the orthopedic patients who received LMWH, there was no significant difference in the frequency of HIT-IgG formation, or in the frequency of possible HIT among patients who received the different LMWH preparations (data not shown).
Fractions indicate the number of patients with positive HIT-IgG test results (by the assay indicated) out of the patient population tested.
Fractions indicate the number of patients with HIT out of the patient population tested.
Fractions indicate the number of patients with HIT out of those who tested positive for HIT-IgG antibodies by the assay indicated.