Introduction Unfractionated heparin (UFH) remains a cornerstone in the treatment of thromboembolic conditions such as deep vein thrombosis (DVT), and pulmonary embolism (PE). The activated partial thromboplastin time (aPTT) is commonly employed to monitor UFH therapy to ensure that the anticoagulation effect remains in the therapeutic range. Subtherapeutic or supratherapeutic aPTT levels can lead to inadequate anticoagulation, increasing the risk of thrombosis, or excessive anticoagulation, raising the risk of bleeding complications, respectively. Guidelines recommend an initial aPTT assessment 6 hours after infusion initiation, and subsequent measurements every 6 hours until therapeutic levels are consistently achieved. This process is labor-intensive and relies on nurses, pharmacists, and phlebotomists. Due to these barriers, low-molecular-weight heparin (LMWH) and direct oral anticoagulants (DOACs) have become better options in many cases. However, there are still conditions where heparin infusion remains the drug of choice, as it allows for rapid dose adjustments. These include, but are not limited to, severe renal impairment, high risk of bleeding or need for rapid reversal, acute coronary syndromes (ACS) when percutaneous coronary intervention is planned, massive PE or DVT with hemodynamic instability, and extracorporeal circulation or device use. Maintaining therapeutic levels of anticoagulation with UFH can be challenging due to the narrow therapeutic range of UFH and variability in pharmacokinetics and pharmacodynamic properties, requiring frequent lab monitoring and dosing adjustments. While researchers have questioned the correlation between aPTT values and clinical outcomes, the impact of delayed or inconsistent aPTT monitoring on the efficacy of heparin therapy was underexplored. This project aims to fill this gap by systematically analyzing how deviations in the timing of aPTT assessments influence the attainment of therapeutic anticoagulation levels.

Goal To assess the impact of timing deviations in aPTT monitoring on the effectiveness of UFH therapy in patients with DVT, PE, ACS, and stroke, with the objective of optimizing anticoagulation protocols to enhance patient outcomes.

Methodology A retrospective cohort study was conducted using data collected from the HCA Florida Westside Hospital pharmacy in a HIPPA-compliant manner. This involved 66 patients who were administered UFH according to the hospital's heparin protocol in January, 2025. Data was collected on the exact times of heparin infusion initiation and subsequent aPTT measurements over a 72-hour period. We accepted a deviation of 1 hour from the 6-hour mark secondary to logistics. Our therapeutic aPTT level (50-92 seconds) was chosen per heparin protocol applicable at the time of infusion administration and remained an all-inclusive range to accommodate for stroke and ACS patients. Logistic regression analysis was employed to determine the association between the timing deviations and the likelihood of aPTT values falling outside the therapeutic range.

Results We collected a total of 267 aPTT readings. Among these, 105 readings (39.3%) were within the therapeutic range while 162 readings (60.7%) were outside the therapeutic range. Out of all blood draws, 219 (82.2%) were performed more than 60 minutes after the scheduled 6-hour interval plus one-hour allowance for logistical deviations, while 48 (17.9%) were drawn more than 60 minutes before the 6-hour schedule minus the same 1-hour allowance. No draws occurred precisely per protocol. When blood draws occurred beyond ±60 minutes from the scheduled 6-hour collection time, the odds of achieving a therapeutic range (TR) aPTT were 0.3 [p= 0.04; 95% confidence interval (CI): 0.20 - 0.73]. Under the same condition, the odds of a non-TR aPTT were 2.58 [p= 0.04, 95% CI: 1.36 - 4.88]. Based on our hospital statistics, we determined that the odds of a non therapeutic range aPTT is 2.4 times higher if blood draw is collected beyond 60 minutes as compared to within 60 minutes.

Conclusion Delayed or inconsistent aPTT monitoring was associated with reduced achievement of therapeutic anticoagulation in patients receiving UFH. Despite a well established protocol, poor compliance, particularly with timely aPTT draws, remained a key barrier. Addressing workflow inefficiencies through interdisciplinary collaboration, better nursing documentation, and EMR optimization may improve adherence and enhance patient safety.

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2025
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