Laboratory Tests for Diagnosing Arterial Thrombosis
The most essential laboratory tests for diagnosing arterial thrombosis include prothrombin time (PT), activated partial thromboplastin time (aPTT), D-dimer, and specific tests for lupus anticoagulant, with additional specialized testing based on clinical suspicion. 1
First-Line Laboratory Tests
- Prothrombin time (PT)/International Normalized Ratio (INR): Evaluates the extrinsic and common pathways of coagulation, helping identify coagulation factor deficiencies or anticoagulant effects 1
- Activated partial thromboplastin time (aPTT): Assesses the intrinsic and common pathways of coagulation and is useful in detecting coagulation abnormalities 1
- D-dimer: Indicates active coagulation and fibrin production, though its diagnostic value in arterial thrombosis may be limited compared to venous thrombosis 1
- Complete blood count (CBC): Essential to evaluate for thrombocytosis, polycythemia, or other hematologic abnormalities that may contribute to thrombotic risk 1, 2
- Fibrinogen levels: Important to assess, as both elevated and decreased levels can contribute to thrombotic risk 1
Specialized Testing for Arterial Thrombosis
Antiphospholipid Syndrome Evaluation
- Lupus anticoagulant (LA) testing: Should include at least two tests based on different principles 1
- Anticardiolipin antibodies: IgG and IgM isotypes 1
- Anti-β2 glycoprotein I antibodies: IgG and IgM isotypes 1
Thrombophilia Testing
- Activated Protein C Resistance (APC-R): To screen for Factor V Leiden mutation 1
- Prothrombin G20210A mutation: Especially in patients with both arterial and venous thrombosis 1
- Protein C and Protein S activity/levels: To evaluate for deficiencies 1
- Antithrombin III activity: To assess for deficiency 1
- Homocysteine levels: Elevated levels are associated with arterial thrombotic risk 1
Global Hemostasis Assessment
- Thromboelastography (TEG) or Rotational Thromboelastometry (ROTEM): Provides information on clot formation, strength, and lysis 1
- Thrombin Generation Assay (TGA): Evaluates overall coagulation potential 1, 2
Patient Selection for Testing
- High priority for testing: Young patients (<50 years) with unprovoked arterial thrombosis, thrombosis at unusual sites, or thrombosis with autoimmune diseases 1, 3
- Moderate priority: Arterial thrombosis with family history of thrombotic disease 1
- Low priority: Elderly patients with arterial thrombosis and clear atherosclerotic risk factors 1, 3
Important Considerations for Laboratory Testing
- Blood samples should be drawn peripherally, especially if the patient has a central line with heparin 1
- For lupus anticoagulant testing, blood collection should occur before starting anticoagulant therapy or after a sufficient period following discontinuation 1
- Double centrifugation is recommended for certain tests to ensure platelet-poor plasma 1
- Testing for lupus anticoagulant should be repeated >12 weeks after initial positive testing to confirm persistence 1
- Patients on anticoagulant therapy may require specialized testing approaches or interpretation 1
Common Pitfalls and Caveats
- Traditional coagulation tests (PT, aPTT) may not fully reflect the complexity of hemostasis and can be misleading in certain conditions 1
- Samples drawn from central lines may show artificially prolonged clotting times due to heparin contamination 1
- Lupus anticoagulant testing may be affected by anticoagulant therapy, requiring direct molecular testing in patients on heparin or with known lupus anticoagulant 1
- Testing for thrombophilia during acute thrombotic events may be misleading due to consumption of natural anticoagulants and acute phase reactions 1
- Interpretation of results should consider preanalytical variables such as sample processing, medication effects, and timing of collection 1, 2
By following this systematic approach to laboratory testing, clinicians can more effectively diagnose the underlying causes of arterial thrombosis and guide appropriate management decisions.