Screening and Diagnosis of Heparin-Induced Thrombocytopenia in the Pediatric Population – A Single Tertiary Center Experience

Introduction:
Heparin-induced thrombocytopenia (HIT) is a serious immune-mediated side effect of heparin. The incidence of HIT in the pediatric population is reported at up to 3.7%, but the diagnostic approach varies considerably in the literature. Since the treatment of HIT is immediate discontinuation and future avoidance of heparin, overdiagnosis of HIT bears serious consequences. At our center, we employ a stepwise approach to laboratory testing for clinically suspected HIT. This involves an initial immunologic (ELISA) screen which, if positive, is followed by one or more confirmatory functional assays. Serotonin release assay (SRA) is the gold standard for diagnosis but is not universally available. Lumi-aggregometry is a functional assay available at our center which is validated against the SRA. In this study, we aimed to determine the proportion of screening ELISA tests at our center that go on to receive a confirmatory diagnosis of HIT by Lumi-aggregometry or SRA.

Methods:
A retrospective cohort study was performed at the Stollery Children’s Hospital, a tertiary pediatric referral center. The study included patients aged 0 to 18 years admitted from 2008 to 2018 who received a HIT screening ELISA test. Data was obtained from the hospital laboratory database. Chart review was performed for patients with a positive HIT screen for the purposes of calculating the 4T score, a clinical scoring system for HIT validated in adults. Data was analyzed descriptively using frequency tables. Logistic regression models were used to assess the relationship between positive HIT screen and demographic variables.

Results:
233 records met inclusion criteria. There were 23 positive or equivocal ELISA results, for a positive screen rate of 9.9%. There was no statistically significant association between positive screen and demographic variables of age (p=0.132), sex (p=0.911), or requesting service (p=0.848). Neonates had the lowest positive screen rate (2.0%) while adolescents had the highest (16.2%). 47.8% of patients with a positive screen had a low clinical risk of HIT based on 4T score, and heparin was never discontinued in these patients. Of the 5 patients (22%) who were switched to alternative anticoagulation, 3 (60%) developed clinically significant bleeding. There was one case of confirmed HIT (0.4%), which was diagnosed based on SRA.

Conclusion:
HIT is rare in the pediatric population at our center, with only one confirmed case over the 10-year study period. HIT should be considered because of its high morbidity and mortality; however, diagnosis should be based on clinical suspicion and both screening and confirmatory testing to minimize false positive diagnoses.