Despite the increasing utilization of mechanical circulatory support (MCS) devices, the 4Ts and heparin-induced thrombocytopenia (HIT) Expert Probability (HEP) scores have not been validated in patients with suspected HIT requiring MCS.

A retrospective cohort study.

At a tertiary university hospital.

Adults with suspected HIT requiring any MCS.

A diagnostic investigation of HIT.

Of the 299 patients included, there were 374 diagnostic investigations of HIT, of which 32 (8.6%) were HIT-probable (heparin PF4 immunoassay optical density ≥1 or positive serotonin release assay). The 4Ts score ≥4 demonstrated a pretest sensitivity of 0.56 (95% confidence interval [CI]: 0.39-0.72) and specificity of 0.8 (95% CI: 0.75-0.83). The HEP score ≥3 demonstrated a pretest sensitivity of 0.31 (95% CI: 0.18-0.49) and specificity of 0.83 (95% CI: 0.79-0.87). The area under the receiver operating characteristic curve for the 4Ts and HEP scores were 0.68 (95% CI: 0.63-0.73) and 0.63 (95% CI: 0.59-0.68), respectively, and were not statistically different (p = 0.21). In patients with an intra-aortic balloon pump, neither the 4Ts nor HEP score had discriminatory ability to differentiate probable HIT. The HEP score had no discriminatory ability in patients with concomitant MCS devices.

The 4Ts and HEP scores have a modest predictive performance for probable HIT in patients requiring MCS devices. A low 4Ts or HEP score does not reliably rule out HIT in patients requiring MCS, and clinical suspicion for HIT should be investigated, utilizing laboratory tests in this population.