Initial Step in Prothrombotic Workup
The initial step in a prothrombotic workup is to obtain prothrombin time (PT), activated partial thromboplastin time (APTT), fibrinogen level, and platelet count as baseline coagulation screening tests. 1
Core Laboratory Tests
The foundational workup should include:
- PT/INR evaluates the extrinsic and common coagulation pathways, though it captures only approximately 4% of thrombin production during the initiation phase 1
- APTT assesses the intrinsic and common pathways and is useful for detecting both inherited and acquired factor deficiencies 1
- Fibrinogen level is critical as hypofibrinogenemia (<1.0 g/L) is often the first coagulation abnormality to develop and should be measured early 1
- Platelet count provides essential baseline data, with critical thresholds of 50 × 10⁹/L in acute bleeding and 100 × 10⁹/L for traumatic brain injury 1
Additional First-Line Testing
When evaluating for inherited or acquired prothrombotic risk factors, the workup should expand to include:
- Protein C, protein S, and antithrombin III levels to screen for inherited thrombophilias 2
- Factor V Leiden and prothrombin gene mutations as common genetic causes 2
- Lupus anticoagulant and anticardiolipin antibodies for acquired thrombophilias 2
- Lipoprotein(a) and homocysteine levels as additional risk factors 2
Critical Timing Considerations
Do not rely on single measurements, as PT/APTT can appear normal while overall coagulation is severely abnormal, particularly in early stages of coagulopathy. 1 Testing should be performed early and repeated during active clinical scenarios, as coagulopathy evolves rapidly 1.
Common Pitfalls to Avoid
- Avoid delaying testing until clinical coagulopathy manifests, as this leads to delayed intervention and worse outcomes 1
- Do not assume normal PT/APTT excludes prothrombotic states, as these tests primarily assess clot initiation rather than global hemostatic function 1
- Ensure proper timing of testing relative to anticoagulant use, as therapeutic anticoagulation will confound results 2
When to Consult Specialists
Consultation with pediatric thrombosis experts or hematology specialists is reasonable when determining which prothrombotic risk factors to assess, as this field evolves rapidly and interpretation requires expertise 2. This is particularly important when initial screening tests are abnormal or when clinical suspicion remains high despite normal basic testing 3.