Diagnosis of Heparin-Induced Thrombocytopenia: Development and Validation of a Predictive Clinical Score Based on Objective Features Identified by a Multivariate Analysis of a Multinational Prospective Study

Background: Diagnosis of heparin-induced thrombocytopenia (HIT) is based on a composite of clinical likelihood and laboratory testing. We aimed to develop a diagnostic score derived from multivariate analysis of clinical features, including platelet count changes, prospectively recorded in patients with suspected HIT. Methods: This multinational observational study (ClinicalTrials.gov no. NCT00748839) included 2280 adult patients with suspected HIT: 1597 (derivation cohort) formed the basis for developing the scoring system, subsequently validated in 683 additional randomly selected patients (validation cohort). HIT was diagnosed by two independent adjudicators based on clinical features, local laboratory data, and the results of a centrally performed serotonin release assay (SRA). Findings: Overall, 56.7% of the patients were treated in an intensive care unit of whom 57.4% received unfractionated heparin; thromboembolism occurred in 12.3%. In the derivation and validation cohorts, 234 (14.7%) and 99 (14.5%) patients, respectively, were diagnosed with HIT. Eight features were positively associated with HIT diagnosis in a multivariate model (in brackets the value assigned for score calculation): unfractionated heparin use (1); therapeutic-dose heparin use (1); cardiac surgery with cardiopulmonary bypass (2); major trauma (3); 5- to 21-day interval from anticoagulant treatment initiation to suspicion of HIT (4); ≥ 40% decrease in platelet count over ≤ 6 days during the last 10 days of anticoagulation exposure (3); thrombotic event, either arterial (3) or venous (3). The C statistic of the model was 0.791 [0.76; 0.82] (p-value 0.70, Hosmer-Lemeshow test). In the validation cohort, the area under the ROC curve was 0.77 [95% CI 0.74-0.80], and HIT prevalence was 2.6% for a score ≤2; 6% for a score of 3–8; and 28.8% for a score >8: Interpretation: This study distinguishes validated clinical features of HIT, permitting improved estimation of its likelihood. Trial Registration: (ClinicalTrials.gov no. NCT00748839) Funding Statement: Programme Hospitalier de Recherche Clinique (French Health Ministry), Sanofi, LFB, Organon SA. Declaration of Interests: Dr. Mullier reports personal fees from Aspen, personal fees from Stago, grants from Werfen, outside the submitted work; Dr. Gruel reports personal fees from Sanofi, personal fees from LFB, other from Stago, personal fees from Aspen, outside the submitted work; . All other authors declare no conflict of interests. Ethics Approval Statement: The study was conducted in accordance with the ethical principles stated in the Declaration of Helsinki, Good Clinical Practice, and relevant French, Swiss and Belgian legal and regulatory requirements regarding data protection. The protocol was approved by French, Swiss and Belgian independent ethics committees. All patients received written information about the study, emphasizing their right to refuse participation or to withdraw at any time. As no experimental interventions were induced from the protocol, no written informed consent was required for inclusion.