Heparin-Induced Thrombocytopenia: Construction of A Pre-Test Diagnostic Score Derived from the Analysis of A Prospective Multinational Database, with Internal Validation

Background

Diagnosis of heparin-induced thrombocytopenia (HIT) requires pre-test probability assessment and dedicated laboratory assays.

Objective

To develop a pre-test score for HIT.

Design

Observational; analysis of prospectively collected data of hospitalized patients suspected with HIT (ClinicalTrials.gov NCT00748839).

Setting

Thirty-one tertiary hospitals in France, Switzerland, and Belgium.

Patients

Patients tested for HIT antibodies (2,280 evaluable), randomly allocated to derivation and validation cohorts.

Measurements

Independent adjudicators diagnosed HIT based on the prospectively collected data and Serotonin Release Assay results.

Results

HIT was diagnosed in 234 (14.7%) and 99 (14.5%) patients in the two cohorts. Eight features were associated with HIT (in brackets, points assigned for score calculation of the score): unfractionated heparin (1); therapeutic-dose heparin (1); cardiopulmonary bypass (cardiac surgery) (2); major trauma (3); 5- to 21-day interval from anticoagulation initiation to suspicion of HIT (4); ≥ 40% decrease in platelet count over ≤ six days (3); thrombotic event, arterial (3) or venous (3). The C-statistic was 0.79 [95% CI, 0.76-0.82]. In the validation cohort, the area under the receiver operating characteristic curve was 0.77 [95% CI, 0.74-0.80]. Three groups of scores were defined; HIT prevalence reached almost 30% in the high-probability group.

Limitation

The performance of the score may depend on settings and practices.

Conclusion

The objective, easy-to-collect, clinical features of HIT we evidenced were incorporated into a pre-test score, which may guide clinical decisions regarding diagnostic testing and anticoagulation.