What is the recommended prothrombotic workup?

Prothrombotic Workup

For venous thromboembolism (VTE), the prothrombotic workup should include testing for Factor V Leiden, prothrombin G20210A mutation, antithrombin deficiency, Protein C and S deficiencies, lupus anticoagulant, anticardiolipin antibodies, anti-β2-glycoprotein-1 antibodies, and Factor VIII levels, particularly after early-onset events, unusual site thrombosis, recurrent thrombosis, or pregnancy-associated thrombosis. 1

Core Laboratory Evaluation for VTE

The standard thrombophilia workup for venous thromboembolism encompasses both inherited and acquired prothrombotic conditions 1:

Inherited Thrombophilias

• Factor V Leiden (R506Q mutation) - test via activated Protein C resistance assay and/or direct genetic testing 1
• Prothrombin G20210A mutation - direct genetic testing 1
• Antithrombin deficiency - functional and antigenic assays 1
• Protein C deficiency - functional assay 1, 2
• Protein S deficiency - functional and free antigen assays 1, 2
• Factor VIII levels - elevated levels increase thrombotic risk 1

Acquired Thrombophilias

• Lupus anticoagulant - requires dilute Russell viper venom time (dRVVT) as the primary screening test, followed by confirmatory testing with high phospholipid concentration 1
• Anticardiolipin antibodies - IgG and IgM isotypes 1, 2
• Anti-β2-glycoprotein-1 antibodies - IgG and IgM isotypes 1

Additional Testing Considerations

• Homocysteine levels - hyperhomocysteinemia is associated with increased thrombotic risk 2, 3, 4
• Complete blood count - to evaluate for myeloproliferative disorders 2

Specific Testing Methodology for Lupus Anticoagulant

The lupus anticoagulant testing requires a specific algorithmic approach 1:

Screening Phase

• Dilute Russell viper venom time (dRVVT) is the most robust and specific first-line test 1
• aPTT with silica activator and low phospholipid content is the second-line screening test 1
• Avoid kaolin-based aPTT (problematic in automated systems) and ellagic acid-based tests (insensitive) 1

Mixing Studies

• Perform 1:1 mixing with pooled normal plasma 1
• Results suggest lupus anticoagulant when clotting times remain prolonged beyond local cut-off values 1
• Must exclude heparin contamination via thrombin time 1

Confirmatory Testing

• Repeat testing at high phospholipid concentration 1
• Calculate percentage correction: [(screen - confirm)/screen] × 100 1
• Positive if percentage correction exceeds local cut-off established from ≥40 healthy donors under age 50 1

Clinical Context for Testing

When to Perform Comprehensive Workup

Testing is particularly indicated in these scenarios 1:

• Early-onset VTE (age <50 years) 2
• Thrombosis at unusual body sites (cerebral venous thrombosis, mesenteric vein thrombosis) 1, 3, 4
• Recurrent thrombotic events 1
• Pregnancy-associated thrombosis 1, 3, 4
• Unprovoked (idiopathic) VTE 1
• Family history of thrombosis 1
• Paradoxical cerebral embolism (suggesting right-to-left shunt) 2

Limited Role in Arterial Thrombosis

For arterial ischemic stroke, routine prothrombotic testing is NOT recommended as inherited coagulation disorders are not established risk factors for arterial events 5. The limited workup for stroke patients should include 2:

• Complete blood count
• Lupus anticoagulant
• Anticardiolipin antibodies
• Plasma total homocysteine

Possible exceptions where arterial stroke may warrant expanded testing include prothrombin G20210A mutation in adults and protein C deficiency in children 5.

Critical Testing Caveats

Timing Considerations

• Avoid testing during acute thrombosis when possible, as acute phase reactants can affect results 1
• Protein C and S levels are reduced by acute thrombosis, warfarin therapy, and liver disease 1
• Antithrombin levels are reduced by heparin therapy and consumptive coagulopathy 1
• Lupus anticoagulant testing is compromised by therapeutic anticoagulation; dRVVT and aPTT reagents can neutralize heparin up to 0.8 U/mL 1

Pregnancy-Specific Adjustments

• Establish pregnancy-specific normal ranges for aPTT (generally shortened due to elevated Factor VIII) and dRVVT 1
• Protein S levels physiologically decrease during pregnancy 1

Laboratory Standardization

• Use locally established cut-off values - do not apply reference ranges from other laboratories even with identical methods and instruments 1
• Pooled normal plasma must be double-centrifuged to ensure platelet count <10^7/mL and stored at -70°C 1

Common Pitfalls to Avoid

• Do NOT test all stroke patients for inherited thrombophilias - this is not evidence-based and leads to unnecessary testing 5
• Do NOT rely on single positive lupus anticoagulant test - requires confirmation on separate occasion at least 12 weeks apart for antiphospholipid syndrome diagnosis 1
• Do NOT interpret mildly elevated antiphospholipid antibodies as clinically significant without appropriate clinical context 5
• Do NOT test during acute illness when results will be unreliable and difficult to interpret 1