What is the initial step in a coagulation workup?

Initial Coagulation Workup

The initial step in a coagulation workup should include early, repeated, and combined measurement of prothrombin time (PT), activated partial thromboplastin time (APTT), fibrinogen (Clauss method), and platelet count, supplemented with viscoelastic testing when available to provide real-time assessment of coagulation function. 1

Standard Laboratory Tests (First-Line)

The foundation of coagulation assessment consists of four essential tests that should be obtained simultaneously:

• PT/INR: Evaluates the extrinsic and common pathways, though it monitors only the initiation phase of coagulation (approximately 4% of thrombin production) 1, 2
• APTT: Assesses the intrinsic and common pathways, useful for detecting inherited and acquired factor deficiencies 1, 2
• Fibrinogen (Clauss assay): Critical as hypofibrinogenemia is often the first coagulation abnormality to develop, with levels <1.0 g/L reached after approximately 150% blood loss 1
• Platelet count: Essential baseline measurement, with critical threshold of 50 × 10⁹/L in acute bleeding (100 × 10⁹/L for traumatic brain injury) 1

Viscoelastic Testing (Strongly Recommended)

Viscoelastic methods (thromboelastometry/thromboelastography) should be performed alongside standard tests to characterize coagulopathy and guide hemostatic therapy in real-time. 1

Advantages of viscoelastic testing:

• Provides results 30-60 minutes faster than conventional laboratory testing 1
• Assesses global hemostasis beyond the initiation phase that PT/APTT capture 1
• Predicts need for massive transfusion and mortality better than conventional tests 1
• Detects coagulopathy that may be missed when PT/APTT appear normal 1
• Can identify hyperfibrinolysis and guide tranexamic acid use 1

Context-Specific Considerations

Trauma/Hemorrhagic Shock Setting

In major trauma with active bleeding, the workup should be:

• Immediate: Tests ordered early and repeated frequently to detect evolving coagulopathy 1
• Combined with metabolic markers: Serum lactate or base deficit to assess shock severity and predict transfusion needs 1
• Point-of-care capable: Portable coagulometers and bedside viscoelastic testing improve turnaround time 1

Bleeding Disorder Evaluation (Non-Acute)

For patients with unexplained bleeding tendency, first-line testing expands to include:

• PT, APTT, fibrinogen, and platelet count (performed by 90-100% of specialists) 3
• Von Willebrand factor antigen and function (84% of specialists) 3
• Factor VIII, IX, and XI assays (62% of specialists) 3
• Full blood count and iron studies/ferritin (65-69% of specialists) 3
• ABO blood group (70% of specialists, as blood type affects VWF levels) 3

Critical Pitfalls to Avoid

• Do not rely on single measurements: PT/APTT can appear normal while overall coagulation is severely abnormal, particularly in early traumatic coagulopathy 1
• Do not delay testing: Fibrinogen drops first and fastest; waiting for clinical coagulopathy before testing leads to delayed intervention and worse outcomes 1
• Do not ignore preanalytical factors: Sample handling, storage temperature, and time to analysis significantly affect results, particularly for APTT 4
• Do not use PT/APTT alone to exclude direct oral anticoagulants (DOACs): Normal PT/APTT does not exclude presence of dabigatran, rivaroxaban, or apixaban 2

Timing and Frequency

• Initial assessment: Within 4 hours of blood collection for baseline accuracy 4
• Repeat testing: Frequent reassessment during active bleeding or resuscitation, as coagulopathy evolves rapidly 1
• Stored samples: Acceptable for additional PT, fibrinogen, and antithrombin testing up to 24 hours at room temperature or 4°C; APTT shows more variability with storage 4