Heparin-induced Thrombocytopenia: Construction of a Pretest Diagnostic Score Derived from the Analysis of a Prospective Multinational Database, with Internal Validation

Background: Diagnosis of heparin-induced thrombocytopenia (HIT) requires pretest probability assessment and dedicated laboratory assays.

Objective: To develop a pretest 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 (2280 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: Heparin-induced thrombocytopenia 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 ≤6 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 pretest score, which may guide clinical decisions regarding diagnostic testing and anticoagulation.