SAN FRANCISCO — The HIT Expert Probability (HEP) Score offers clinicians a new tool to help detect heparin-induced thrombocytopenia earlier, according to a presenter here. 

Currently, there is no way to predict heparin-induced thrombocytopenia (HIT), and patients in whom it is suspected must be taken off of unfractionated heparin and transitioned to a direct thrombin inhibitor until the diagnosis is confirmed. 

“Current pre-test probability scoring models, when used in conjunction with serological assays, yield false positives, and 4 Ts is limited by low positive predictive value,” Heidi M. Felix, MPAS, PA-C, chief PA in the department of trauma surgery at Allegheny Health Network and Forbes Regional Hospital in Monroeville, Pennsylvania, said during a poster session at the American Academy of Physician Assistants 2015 meeting.

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To validate the HEP Score’s sensitivity, specificity, and positive and negative predictive values, Felix and colleagues performed a retrospective analysis of 100 adults referred for heparin-induced thrombocytopenia (HIT). Previously, only one study by Cuker et al assessed the HEP Score’s performance.

In the current study, 79 patients aged older than 18 years who had a diagnosis of thrombocytopenia during hospitalization were included in the study. Mean patient age was 67 years, 87% were white, 92% had received unfractionated heparin, and mean PF4/polyanion-enzyme immunoassay (EIA) score was 0.69. 

In this validation study, the HEP Score had a sensitivity of 78.9% (95% CI: 63.6, 94.3), which was lower than the original study (100%), and a specificity of 71.7% (95% CI: 62.1, 81.2) which was higher (60%), the researchers found. 

The negative predictive value was 91.5% (95% CI: 84.8, 98.2%), and the positive predictive value was 46.9% (95% CI: 32.4, 61.4) — better than previously reported positive predictive values for the 4 Ts (9% to 17%).

“The HEP Score has the potential to reduce the transition to direct thrombin inhibitors, patient complications, length of stay and medical care costs,” Felix said.

The tool still needs to be validated in other populations, as this was the first cohort of both HIT positive and negative patients used to assess the HEP Score’s performance, she added.


  1. Felix HM et al. “Validating the HEP Score.” Presented at: AAPA 2015. May 23-27, 2015. San Francisco, California.