From the Guidelines
The aPTT value of 35 seconds is within the normal range, indicating normal blood clotting function, and no intervention is required as this result suggests appropriate coagulation activity. The activated partial thromboplastin time (aPTT) measures the effectiveness of the intrinsic and common coagulation pathways, specifically assessing factors VIII, IX, XI, XII, and other clotting factors. A normal aPTT indicates that these pathways are functioning properly, and the patient does not have a bleeding disorder related to these factors.
Key Considerations
- If the patient is on heparin therapy, this value suggests they are not receiving therapeutic anticoagulation, as therapeutic heparin typically extends the aPTT to 1.5-2.5 times the normal range (approximately 60-100 seconds) 1.
- For patients with thrombotic conditions requiring anticoagulation, this level would be insufficient, while for those not requiring anticoagulation, this normal result is reassuring.
- The normal range for aPTT using the Dade Actin FS reagent is 27 to 35 seconds, as indicated in the study by Cruickshank et al. 1.
Monitoring and Adjustment
- Measurements should be made 6 h after any dosage change and used to adjust UFH infusion until the aPTT exhibits a therapeutic level 1.
- When 2 consecutive aPTT values are therapeutic, the measurements may be made every 24 h and, if necessary, dose adjustment performed.
- A significant change in the patient's clinical condition (e.g., recurrent ischemia, bleeding, or hypotension) should prompt an immediate aPTT determination, followed by dose adjustment, if necessary. Some key points to consider in the management of patients on heparin therapy include:
- Serial hemoglobin/hematocrit and platelet measurements are recommended at least daily during UFH therapy 1.
- Serial platelet counts are necessary to monitor for heparin-induced thrombocytopenia.
- A high clinical suspicion of heparin-induced thrombocytopenia mandates the immediate cessation of all heparin therapy.
From the Research
Patient aPTT Results
- The patient's aPTT result is 35 seconds, which is below the normal range of 60 seconds or more, as indicated in the study 2.
- According to the study 2, an aPTT value of less than 60 seconds is associated with an increased risk of recurrent cardiovascular events.
- The study 3 compared the use of aPTT and activated coagulation time (ACT) for monitoring anticoagulation in patients undergoing extracorporeal membrane oxygenation (ECMO) therapy, and found that the aPTT group had fewer heparin dose changes and a lower cumulative heparin dose per day.
Comparison of aPTT and Other Monitoring Tests
- The study 4 compared the use of aPTT and antifactor-Xa for monitoring therapeutic unfractionated heparin, and found no difference in the outcomes of bleeding or thrombosis.
- The study 5 compared the incidence of bleeding and thrombosis between adult venoarterial ECMO patients managed with an ACT-guided heparin anticoagulation protocol and an aPTT protocol, and found no difference in the incidence of bleeding or thrombosis between the two groups.
Clinical Implications
- The patient's low aPTT result may indicate a need for adjustment of their heparin dose, as suggested by the study 3.
- The choice of monitoring test for unfractionated heparin therapy, such as aPTT or antifactor-Xa, may not affect the outcomes of bleeding or thrombosis, as indicated by the study 4.
- Further studies are needed to determine the optimal anticoagulation strategy for patients undergoing ECMO therapy, as suggested by the study 5.