Assessing the Impact of a Heparin Induced Thrombocytopenia Recognition and Management Protocol

Abstract 2080

Heparin-induced thrombocytopenia (HIT) is an immune mediated adverse reaction to heparin which results in significant patient morbidity. Although guidelines for the management of HIT highlight which patients should receive initial therapy, they fall short of directing decisions regarding continuation of therapy after HIT antibody test results return. Using a multidisciplinary approach, a comprehensive HIT Recognition and Management Protocol was developed. Protocol implementation involved a change in HIT testing from a polyspecific platelet factor 4 (PF4)/heparin ELISA to an IgG-specific PF4/heparin ELISA. The use of automatic send out serotonin release assay (SRA) testing for those with a positive PF4/heparin ELISA optical density between 0.4 and 2 was also implemented. The protocol was initiated on October 15^th 2010. The overall goal of this project was to assess the impact of protocol implementation on HIT management.

A retrospective observational cohort study using a pre – post design was used. Patients started on direct thrombin inhibitor therapy (DTI) from September 1^st 2009- February 28^th 2010 for suspected/confirmed HIT composed the pre implementation group while those started on DTI therapy from November 1^st 2010 – April 30^th 2011 composed the post implementation group. Data extraction involved demographic, clinical, laboratory and pharmacy data. DTI initiation within 12 hours of HIT laboratory testing in patients with an intermediate to high 4Ts score was assessed. Additional endpoints included appropriate discontinuation of DTI therapy defined as discontinuation within 12 hours of a negative PF4/heparin ELISA or within 12 hours of a negative SRA in patients with a positive PF4/heparin ELISA with an optical density below 2. Hours of inappropriate continuation of DTI therapy and appropriate warfarin transition were also assessed. T- test, Chi square and Mann Whitney U were used to analyze data with a level of significance set at p <0.05.

A total of 61 patients received DTI therapy for suspected/confirmed HIT in the pre period compared to 46 in the post period. DTI initiation within 12 hours of a PF4/heparin ELISA order for those with an intermediate-high 4T score occurred in 8/31 (25.8%) of pre patients and 24/31 (77.4%) of post patients, p <0.0001. Appropriate discontinuation of DTI therapy after a negative PF4/heparin ELISA occurred in 5/23 (21.7%) of pre patients and 12/26 (46.2%) of post patients, p = 0.07. Total hours of inappropriate continuation of DTI therapy after a negative PF4/heparin ELISA test were 2607.8 hours in the pre and 740.5 hours in the post periods. The median number of hours of inappropriate DTI continuation/patient after a negative PF4/heparin ELISA in the pre versus post periods were 99.6 and 25.1 hours respectively, p=0.04. Appropriate discontinuation of DTI therapy after a negative SRA occurred in 2/13 (15.4%) pre and 2/9 (22.2%) post patients, p =0.12.

Seventeen patients in the pre and 10 in the post period were transitioned to warfarin for HIT. Initiation occurred after platelet count recovery to 150 × 10⁹/L in 11/17 (64.7%) of pre and 7/10 (70%) of post patients, p = 0.78. The initial warfarin dose was < 5mg in 15/17 (88.2%) of pre and 10/10 (100%) of post patients, p =0.26. A minimum 5 day overlap of DTI and warfarin therapy occurred in 11/16 (68.8%) pre and 8/9 (88.9%) of post patients, p =0.26.

Implementation of the HIT protocol improved the timely initiation of DTI therapy in those with an intermediate-high 4Ts score and was successful in promoting appropriate discontinuation of DTI therapy after a negative PF4/heparin ELISA test. Automatic send out SRA testing did not demonstrate a benefit in promoting discontinuation of therapy in those with a positive PF4/heparin ELISA and a negative SRA.