How is APTEM (Activated Partial Thromboplastin Time, Endogenous Thrombin Potential, and Clot Lysis) testing used to guide the administration of antifibrinolytic agents in patients with suspected hyperfibrinolysis?

APTEM Testing for Guiding Antifibrinolytic Therapy in Hyperfibrinolysis

APTEM testing should be used to guide antifibrinolytic therapy in patients with suspected hyperfibrinolysis, with administration of tranexamic acid (10-15 mg/kg followed by 1-5 mg/kg/hour infusion) only when hyperfibrinolysis is confirmed by thromboelastometric monitoring. 1

Understanding APTEM Testing

APTEM is a specialized thromboelastometric test that helps identify hyperfibrinolysis by comparing:

• Standard EXTEM (tissue factor activated) results with APTEM (aprotinin-inhibited) results 2
• Significant improvement in clot parameters in APTEM compared to EXTEM indicates hyperfibrinolysis 2
• Key parameters evaluated include maximal clot firmness (MCF) and clot lysis index at 30 minutes (CLI30) 2

Diagnostic Thresholds for Hyperfibrinolysis

APTEM testing provides specific thresholds to identify hyperfibrinolysis:

• MCF-EXTEM threshold of 18mm (100% sensitivity, 100% specificity) 2
• CLI30 threshold of 71% (75% sensitivity, 100% specificity) 2
• Increase of MCF-APTEM threshold of 7% (80% sensitivity, 100% specificity) 2

Antifibrinolytic Therapy Protocol

When hyperfibrinolysis is confirmed by APTEM testing, the recommended antifibrinolytic therapy includes:

• Tranexamic acid: 10-15 mg/kg loading dose followed by 1-5 mg/kg/hour infusion 1, 3
• Alternative: ε-aminocaproic acid 100-150 mg/kg followed by 15 mg/kg/hour 1
• Continue therapy until bleeding is adequately controlled 1
• Monitor for resolution of hyperfibrinolysis with serial APTEM testing 1

Clinical Application and Considerations

When to Use APTEM Testing

• Trauma patients with significant bleeding or at risk of significant hemorrhage 1, 4
• Patients with suspected hyperfibrinolysis based on clinical presentation 1
• Cases where empiric antifibrinolytic therapy might pose risks 4

Cautions and Contraindications

• Antifibrinolytic agents should not be used routinely without confirmed hyperfibrinolysis 1
• Routine use in cancer-related DIC is not recommended due to potential thrombotic risks 1
• Patients with fibrinolytic shutdown may experience adverse effects from antifibrinolytic therapy 4

Special Considerations

Trauma Patients

• APTEM testing allows rapid detection of hyperfibrinolysis in severely injured trauma patients 2
• Patients with confirmed hyperfibrinolysis have higher injury severity scores, greater coagulation abnormalities, and higher mortality rates 2
• Early identification and targeted treatment can reduce need for allogeneic blood products 5

Cancer-Related DIC

• Routine use of antifibrinolytic agents in hyperfibrinolytic DIC is not recommended 1
• Consider tranexamic acid only if therapy-resistant bleeding dominates the clinical picture 1
• Regular monitoring is essential to detect complications including organ failure 1

Pharmacokinetic Considerations

• Tranexamic acid has a plasma half-life of approximately 120 minutes 1, 3
• A plasma concentration of 10 μg/ml is required to inhibit fibrinolysis 1, 3
• Additional dosing may be needed to maintain therapeutic levels during prolonged procedures 6
• Pharmacokinetic studies show that concentrations may fall below therapeutic levels during initial hospital treatment 6

Monitoring Therapy Effectiveness

• Continue APTEM monitoring during treatment to assess response 1
• Discontinue antifibrinolytic therapy once bleeding is controlled 1
• Monitor for potential thrombotic complications, especially in patients with risk factors 4