APTEM and Its Monitoring in Clinical Practice
APTEM (Aprotinin-modified EXTEM) is a specialized viscoelastic test used in rotational thromboelastometry (ROTEM) to detect and characterize hyperfibrinolysis by neutralizing fibrinolytic activity with aprotinin, allowing differentiation between fibrinolysis-driven coagulopathy and other causes of impaired clot formation.
What is APTEM?
APTEM is a modification of the standard EXTEM test in ROTEM analysis where aprotinin (a fibrinolysis inhibitor) is added to the sample. The test is specifically designed to:
- Identify hyperfibrinolysis by comparing APTEM results with standard EXTEM results 1
- Guide antifibrinolytic therapy (such as tranexamic acid) in bleeding patients 1
- Characterize coagulopathy in trauma, cardiac surgery, and other bleeding scenarios where fibrinolysis may be contributing to blood loss 1
Clinical Context and Role
Viscoelastic Testing in Trauma and Bleeding
Viscoelastic methods (including ROTEM with APTEM) should be performed to assist in characterizing coagulopathy and guiding hemostatic therapy in bleeding patients 1. The European trauma guidelines strongly recommend this approach because:
- Standard coagulation tests (PT/aPTT) monitor only the initiation phase of coagulation, representing just 4% of thrombin production 1
- Viscoelastic testing provides real-time, comprehensive assessment of clot formation, strength, and fibrinolysis 1
- Turn-around time is significantly shorter (30-60 minutes faster) compared to conventional laboratory testing 1
- Variables of clot firmness predict massive transfusion needs, thrombotic events, and mortality 1
Limitations in Elderly Trauma
There is insufficient evidence to support routine use of ROTEM (including APTEM) specifically in elderly trauma patients, and further studies are necessary to determine their role in this population 1. Standard coagulation assays (aPTT, PT, INR, anti-Xa) remain the recommended first-line tests 1.
How APTEM Works: Interpretation Algorithm
Step 1: Perform Simultaneous EXTEM and APTEM
- Run both tests in parallel on the same blood sample
- EXTEM shows baseline clot formation without fibrinolysis inhibition
- APTEM shows clot formation with aprotinin blocking fibrinolysis
Step 2: Compare Results
If APTEM shows improved clot firmness compared to EXTEM:
- This indicates hyperfibrinolysis is present and contributing to coagulopathy 1
- Consider antifibrinolytic therapy (tranexamic acid) 1
- Important caveat: In general, patients with DIC should NOT be treated with antifibrinolytic agents, except in cases characterized by primary hyperfibrinolytic state with severe bleeding 2
If APTEM and EXTEM show similar poor results:
- Hyperfibrinolysis is not the primary problem
- Focus on other causes: factor deficiency, platelet dysfunction, low fibrinogen 1
Step 3: Guide Therapy Based on Findings
- Hyperfibrinolysis detected: Administer lysine analogues such as tranexamic acid (e.g., 1 g every 8 hours) 2
- No hyperfibrinolysis: Pursue other hemostatic interventions (FFP, fibrinogen concentrate, platelets) based on other ROTEM parameters 1
Monitoring Considerations and Pitfalls
Common Pitfalls to Avoid
Don't rely on APTEM alone: It must be interpreted alongside standard EXTEM and other ROTEM parameters (FIBTEM for fibrinogen assessment) 1
Recognize DIC contraindication: Patients with DIC and thrombosis predominance should generally NOT receive antifibrinolytics even if APTEM suggests hyperfibrinolysis 2
Understand limitations in inflammatory states: While viscoelastic testing is less affected by inflammation than aPTT, interpretation should still consider the clinical context 1
Need for standardization: Methods employed by different investigators differ significantly, highlighting the need for institutional protocols 1
Integration with Standard Coagulation Monitoring
Routine coagulation monitoring should include early, repeated, and combined measurement of PT, aPTT, fibrinogen, and platelets, WITH viscoelastic methods (including APTEM when available) to assist in characterizing coagulopathy 1.
- Monitor PT, aPTT, platelets, and fibrinogen every 24-72 hours in critically ill bleeding patients 1
- Use anti-Xa assay rather than aPTT for UFH monitoring in hyperinflammatory states, as aPTT may be unreliable and lead to heparin overdose 1
- Viscoelastic testing provides complementary real-time information that standard tests cannot capture 1
Specific Clinical Scenarios
Trauma Patients
- APTEM is particularly valuable in detecting acute traumatic coagulopathy with hyperfibrinolysis 1
- Early variables of clot firmness predict massive transfusion requirements 1
Cardiac Surgery
- Hyperfibrinolysis is common post-cardiopulmonary bypass 1
- APTEM can guide targeted antifibrinolytic therapy