What are common coagulation studies?

Common Coagulation Studies

The most essential common coagulation studies include prothrombin time (PT), activated partial thromboplastin time (APTT), fibrinogen levels, and platelet count, which should be measured early and repeatedly to detect coagulopathy. 1

First-Line Coagulation Studies

Basic Coagulation Panel

• Prothrombin Time (PT)/International Normalized Ratio (INR)

  • Measures the extrinsic pathway and common pathway of coagulation
  • Used for monitoring vitamin K antagonist therapy (e.g., warfarin)
  • Normal PT is typically reported in seconds; INR is used primarily for anticoagulation monitoring 2, 3
  • Note: INR was developed specifically for monitoring vitamin K antagonists and may not be appropriate in other clinical settings 4

• Activated Partial Thromboplastin Time (APTT)

  • Evaluates the intrinsic and common pathways of coagulation
  • Used for monitoring unfractionated heparin therapy
  • Reported in seconds or as a ratio of patient-to-normal clotting time 4

• Fibrinogen

  • Measured by either Clauss method (direct) or derived method
  • Critical for clot formation
  • Low levels (<1.3 g/L) are associated with increased mortality in trauma patients 1

• Platelet Count

  • Essential component of hemostasis
  • Thrombocytopenia may indicate sepsis, consumption, or other disorders
  • In COVID-19, platelet count <150 × 10^9/L was observed in 36.2% of patients 1

Additional First-Line Tests

• Complete Blood Count (CBC)

  • Provides context for coagulation abnormalities
  • 65% of specialists include this in first-line testing 1

• ABO Blood Group

  • Influences von Willebrand factor levels
  • 70% of specialists include this in first-line testing 1

• D-dimer

  • Fibrin degradation product
  • Elevated in active coagulation and fibrinolysis
  • Particularly important in COVID-19 coagulopathy assessment 1

Second-Line Coagulation Studies

• Factor Assays

  • Factor VIII, IX, XI (intrinsic pathway)
  • Factor II, V, VII, X (extrinsic pathway)
  • Factor XIII (fibrin stabilization)
  • Used when basic testing suggests factor deficiency 1

• Platelet Function Testing

  • Light transmission aggregometry
  • Platelet function analyzer (PFA-100/200)
  • Platelet nucleotides or release assay
  • 60% of specialists use these as second-line tests 1

• Viscoelastic Testing

  • Thromboelastography (TEG)
  • Rotational thromboelastometry (ROTEM)
  • Provides real-time assessment of clot formation, strength, and dissolution
  • Recommended to assist in characterizing coagulopathy and guiding hemostatic therapy 1
  • Particularly useful in trauma, liver disease, and cardiac surgery settings 1

• Fibrinolysis Assays

  • Assess the breakdown of blood clots
  • 38% of specialists use these as second-line tests 1

• Thrombin Generation Assay

  • Measures overall thrombin production capacity
  • 28% of specialists use this as a second-line test 1

Clinical Applications and Considerations

Trauma and Critical Care

• In trauma patients, early and repeated measurement of PT/INR, APTT, fibrinogen, and platelets is recommended 1
• Viscoelastic methods can provide faster results (30-60 minutes quicker) than conventional testing 1
• D-dimer, PT, and platelet count (in decreasing order of importance) are recommended for all COVID-19 patients 1

Liver Disease

• Traditional tests (PT/INR, APTT) may be misleading in liver disease as they only evaluate initiation phase of coagulation 1
• Global tests of hemostasis (thrombin generation tests, TEG/ROTEM) may better reflect the rebalanced hemostasis in cirrhosis 1

Bleeding Disorders

• For suspected bleeding disorders, specialists commonly perform PT, APTT, von Willebrand factor assays, and factor VIII, IX, and XI assays 1
• Bleeding assessment tools (BATs) are used by 80% of specialists to guide testing strategy 1

Important Caveats

1. Sample Collection and Storage

   • Proper collection techniques are essential for accurate results
   • PT samples are stable for up to 24 hours at room temperature or refrigerated
   • APTT samples are stable for up to 12 hours at room temperature or refrigerated 5

2. Interpretation Limitations

   • PT/INR and APTT only reflect the initiation phase of coagulation (first 4% of thrombin production) 1
   • Normal PT/APTT does not exclude significant coagulation disorders 1
   • In liver disease, INR may not accurately reflect bleeding risk 1

3. Viscoelastic Testing Considerations

   • Lack of standardization between different centers is a limitation 1
   • Interpretation requires specific training and understanding of the methodology
   • May underestimate coagulation capacity in some settings 1

By understanding these common coagulation studies and their appropriate applications, clinicians can better assess hemostatic function and guide therapeutic interventions in various clinical scenarios.