Inpatient Monitoring of Unfractionated Heparin

Unfractionated heparin (UFH) is the most widely used intravenous (IV) anticoagulant for the treatment and prevention of thromboembolic disease (e.g., blood clots ). When administered by intravenous injection, the onset of action is immediate. Indications for use of UFH include venous thromboembolism, acute coronary syndrome, and acute ischemic stroke. UFH is used to prevent thrombosis in the setting of arrhythmias, extracorporeal membrane oxygenation (ECMO), cardiopulmonary bypass (CPB), and endovascular procedures. The unpredictable pharmacokinetics of UFH and interpatient variability result in a narrow therapeutic index restricting its use to the hospital setting with close monitoring and adjustments.

Two validated assays exist and are in use at the VUMC adult hospital for the monitoring of unfractionated heparin: 1) the activated partial thromboplastin time (PTT) and 2) the chromogenic anti-factor Xa assay (anti-Xa). At VUMC, the PTT protocol is managed by nursing; the anti-Xa protocol is managed by clinical pharmacy. Both are clinically acceptable methods for titration and adjustment of unfractionated heparin. Assessing the therapeutic effect of unfractionated heparin is most often performed with the PTT, which requires institutional calibration to a specific heparin level to account for the variable PTT responses with different commercial reagents and laboratory instruments. The PTT can be influenced by various elements during sample processing, laboratory analysis, and patient biological factors that may cause it to be an inaccurate indication of the degree of anticoagulation. This can lead to patients not getting the correct heparin dosing for their clinical needs.

The anti-Xa assay is another method of measuring the degree of therapeutic effect of heparin. In routine clinical practice the anti-Xa is not as widely available and less familiar among many providers. This assay can be impacted by variability in sample collection and processing and laboratory analysis. Compared to the PTT assay, however, it is much less influenced by patient-specific biological factors. This may help improve heparin monitoring and titration to ensure patients receive therapeutic levels of anticoagulation and do not get too much or too little heparin. However, large studies using anti-Xa for management of heparin in the treatment of venous thromboembolism have not been performed.

PTT and anti-Xa heparin monitoring protocols have not been compared in a prospective, randomized setting. The study team will conduct a pragmatic, randomized clinical trial comparing the effectiveness of both methods for optimal monitoring of intravenous unfractionated heparin for systemic anticoagulation in hospitalized adult patients.

• Measurements in therapeutic anticoagulation range [Time frame: Randomization to hospital discharge at approximately 5-7 days post-randomization]
• Coagulation laboratory measurements [Time frame: Randomization to hospital discharge at approximately 5-7 days post-randomization]
• Heparin rate changes [Time frame: Randomization to hospital discharge at approximately 5-7 days post-randomization]
• New thrombotic events [Time frame: Randomization to hospital discharge at approximately 5-7 days post-randomization and for 24 hours after anticoagulation cessation.]
• New clinically relevant bleeding events [Time frame: Randomization to 48 hours after anticoagulation cessation, approximately 5-7 days post-randomization]
• New coagulation events [Time frame: Randomization to 48 hours after anticoagulation cessation, approximately 5-7 days post-randomization]