Inter-Observer Agreement and Laboratory Correlation of the 4T Scoring Model for Heparin-Induced Thrombocytopenia: A Single-Center Retrospective Study and Literature Review

<b>Background</b>: Heparin-induced thrombocytopenia (HIT) is a rapid, life-threatening adverse drug reaction, with the widely used 4T score being the critical clinical tool guiding the need for serological confirmation. This study aimed to validate the diagnostic utility of the 4T score and evaluate its application in a tertiary hospital in Saudi Arabia. <b>Methods</b>: In this retrospective cohort study, we analyzed 449 patients with suspected HIT, comparing their initially recorded clinical 4T scores with those recalculated by trained specialists, using the anti-PF4/heparin IgG ELISA as the reference standard for HIT confirmation. <b>Results</b>: Of the 292 patients who underwent laboratory testing, the HIT positivity rate was 6.5% (<i>n</i> = 19). The primary finding was a markedly low agreement (15.4%) between the system-recorded and the standardized physician-calculated 4T scores, indicating significant inter-observer variability. Despite this, higher calculated 4T scores remained significantly associated with positive HIT test results, and the anti-PF4/heparin IgG ELISA demonstrated 100% sensitivity and 100% negative predictive value (NPV). <b>Conclusions</b>: While the 4T score is indispensable for guiding the diagnostic pathway, the observed profound inter-observer variability highlights an urgent need for standardized scoring training and protocol refinement to enhance diagnostic accuracy and reduce inappropriate therapeutic interventions.