LACK OF IN-VITRO CROSS-REACTIVITY PREDICTS SAFETY OF LOW-MOLECULAR-WEIGHT HEPARINS IN HEPARIN-INDUCED THROMBOCYTOPENIA

Alternative anticoagulation in patients with heparin-induced thrombocy topenia (HIT) is often problematic. The relatively high cross-reactivi ty rate reported for the low-molecular-weight heparins (LMWH) has disc ouraged their use in this setting. This study has investigated the saf ety of using the LMWH Fragmin, based on a negative heparin-dependent p latelet aggregation test using the latter, in patients with proven HIT . Fifty-three evaluable patients with clinical and laboratory evidence of HIT were evaluated for cross-reactivity with Fragmin using a Fragm in-dependent platelet aggregation test. In 20 of 38 patients who showe d no in vitro cross-reactivity, Fragmin was substituted for unfraction ated heparin. The outcome of these 20 patients was evaluated and compa red to that of the remaining 33 patients, in whom anticoagulates were ceased or warfarin or Orgaran was used. Eighteen of 20 patients treate d with Fragmin increased their platelet count by greater than or equal to 50 x 10(9)/l from a mean nadir of 57.9 +/- 4.7 x 10(9)/l within 2. 8 +/- 0.29 days following substitution of Fragmin for unfractionated h eparin. Twenty-eight of the 33 remaining patients who did not receive Fragmin increased their platelet count by greater than or equal to 50 x 10(9)/l from a mean nadir of 53.0 +/- 4.8 x 10(9)/l within 3.0 +/- 0 .29 days. In seven patients (two treated with Fragmin), response could not be evaluated due to death within 36 h of cessation of heparin or discharge from hospital. The results indicate that in vitro cross-reac tivity testing employing a heparin-dependent platelet aggregation assa y can be safely used to select patients with HIT for further anticoagu lation with LMWH.