Global multicenter study establishes the reference range for ISTH Bleeding Assessment Tool scores in individuals under 18 years: communication from the SSC of the ISTH

The International Society on Thrombosis and Haemostasis Bleeding Assessment Tool (ISTH-BAT) is widely used to screen inherited bleeding disorders. Adult reference ranges are age- and sex-specific. However, a single reference range (0-2) is currently applied to all individuals under 18 years. Adolescence' developmental changes and global differences in healthcare access may influence bleeding scores, necessitating validation in a large international pediatric cohort. We aimed to evaluate age- and sex-specific ranges for ISTH-BAT scores in individuals<18 years using international dataset. Under the auspices of two ISTH Scientific Subcommittees, healthy participants <18 were recruited from 7 countries across 5 continents. ISTH-BAT assessments were completed by trained investigators and standard protocol. Participants were stratified by age quartile, sex, country, and World-Bank-income. Reference ranges were defined using the 2.5th-97.5th percentile and assessed by 95% Confidence Interval. A total of 1,168 participants were included (mean age 7.7±5.2 years; 50.5% female). The overall reference range was 0-2. Quartile differences weren't significant (p = 0.065), but a significantly positive age-related trend of increase in BAT score >0 was observed (p < 0.001). Females more often had a bleeding score >0 (p = 0.02), with significant sex differences observed only among Q4 (p=0.003). The 2.5th-97.5th percentile for Q4 females was 0-3. Scores varied by country and income classification (p ≤ 0.001), but reference ranges remained stable. We conclude ISTH-BAT reference range of 0-2 is appropriate for individuals <18 years. For females (12-17 years), 0-3 may be considered and interpreted in conjunction with clinical context when guiding referral decisions.