Evaluation of 4T's scoring system in the identification of heparin-induced thrombocytopenia in patients with mechanical circulatory support

A Modified 4Ts Score for Heparin-Induced Thrombocytopenia in the Mechanical Circulatory Support Population

OBJECTIVE

To identify risk factors and develop a pretest scoring system to differentiate patients with heparin-induced thrombocytopenia (HIT) in the mechanical circulatory support (MCS) population. The authors present a modified "4TMCS" scoring system, which considers the "type of mechanical circulatory support" that may help identify patients at risk for developing postoperative HIT.

DESIGN

A retrospective cohort study. Patients who underwent cardiac surgery were categorized into 3 groups: (1) normal platelet count, (2) thrombocytopenia with a negative HIT test, and (3) thrombocytopenia with a positive HIT test. A comparison of diagnostic accuracy between the 4Ts and 4TMCS probability scores was performed.

SETTING

At a single adult tertiary-care center.

PARTICIPANTS

A total of 5,314 patients who underwent cardiac surgery between May 1, 2008 and December 31, 2016.

INTERVENTIONS

None.

MEASUREMENTS AND MAIN RESULTS

In total, 125 out of 5,314 patients (2.4%) were diagnosed with HIT, of whom 75 out of 5,314 (1.4%) had clinical evidence of thrombosis. Overall, in-hospital mortality was 25.6%, 11.7%, and 1.5% in the HIT(+), HIT(-), and control groups, respectively (p < 0.001). Mechanical circulatory support was associated with a significantly increased risk for HIT, with an incidence of 5.9% in patients receiving MCS versus 1.9% in those without (p < 0.001). Area under the receiver operator curve (AUC) analysis demonstrated improved diagnostic accuracy of the 4TMCS score compared with the 4Ts (AUC = 0.83 v 0.77, p < 0.044). The 4TMCS score had higher sensitivity than the 4Ts, using the guideline-recommended score cutoff of ≥4 (95.2% v 85.7%).

CONCLUSION

Heparin-induced thrombocytopenia is associated with worse outcomes and increased morbidity and mortality in the MCS population. Awareness of patient risk factors and the application of a modified 4TMCS probability score may allow for more accurate screening and treatment of HIT in the MCS population.

Incidence of Heparin-Induced Thrombocytopenia in Patients With Newly Implanted Mechanical Circulatory Support Devices

BACKGROUND

Heparin exposure and device-related thrombocytopenia complicate the diagnosis of heparin-induced thrombocytopenia (HIT) in patients receiving mechanical circulatory support (MCS). To improve anticoagulation management for patients with newly implanted MCS devices, incidence of confirmed HIT needs to be further characterized.

OBJECTIVES

The purpose of this study is to describe the incidence of HIT and clinical utility of the 4Ts score in patients with newly implanted MCS devices.

METHODS

This is a retrospective analysis of MCS patients receiving unfractionated heparin from 2014 to 2017. The primary end point was incidence of laboratory-confirmed HIT. Strong positive, likely positive, low probability, and negative HIT categories were established based on heparin-induced platelet antibody (HIPA) and serotonin release assay (SRA). Secondary end points include characterization of platelet trends, argatroban use, incidence of HIT among each of the MCS devices, and utility of 4Ts score.

RESULTS

A total of 342 patient encounters met inclusion criteria, of which 68 HIPA tests and 25 SRAs were ordered. The incidence of HIT was 0.88% (3/342) and 4.4% (3/68) in patients with suspected HIT. Of the 68 HIPA tests, 3 (4.4%) were considered strong positive and 3 of the 25 SRAs were positive. Median 4Ts score was 4 [2.5-4] and optical density 0.19 [0.11-0.54]. The positive predictive value for the 4Ts score was 0.15 (CI = 0.03-0.46) and negative predictive value, 0.93 (CI = 0.82-0.98).

CONCLUSION AND RELEVANCE

HIT occurs infrequently with newly implanted MCS devices. The 4Ts score appears to have a high negative predictive value for ruling out HIT.