To determine the applicability of the 4Ts score and the heparin-induced thrombocytopenia (HIT) Expert Probability (HEP) score in children with suspected HIT and to estimate the number of children potentially at risk of HIT.
We retrospectively estimated 4Ts and HEP scores in a cohort of 50 children referred for laboratory screening with enzyme immunoassay (EIA). In addition, minor modifications were introduced to the 4Ts score (modified 4Ts score) to adapt it for use in the pediatric setting. All positive EIAs were tested with serotonin release assay (SRA). We also extracted the number of patients started on heparins in a similar period of time.
Median age at the time of testing was 4 years (25-75 percentile 8.7 months – 13.5 years); 78% of patients had low and 22% had intermediate risk pretest probability scores using the original 4Ts score; 86% had low risk and 14% had intermediate risk scores using the modified 4Ts score; 54% of children had a HEP score ≥2. Six (12%) patients had a positive (≥0.40 optical density units) EIA but none had a positive SRA. Based on anticoagulation dose, there were 1-2 new daily potentially high-risk exposures to heparinoids at our institution.
The modified 4Ts and original 4Ts scores may be more adequate than the HEP score to determine HIT pretest probability in children. Despite the number of patients potentially at risk, HIT is rare in pediatrics.

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