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Coagulation Disorder Workup Algorithm (ISTH)

Coagulation Disorder Workup Algorithm (ISTH): Abnormal Coagulation Tests → Pre-Analytic Check → Pattern of Abnormality → Isolated PT Prolongation → Mixi...

Interactive Decision Tree

Mini Map

Algorithm Steps

  1. ▶
    Start

    Abnormal Coagulation Tests

    PT and/or PTT prolonged

    1. ●
      Action

      Pre-Analytic Check

      Rule out artifacts

      • Proper fill (9:1 blood:citrate)
      • Hemolysis, lipemia, icterus
      • Sample age (<4 hours for PTT)
      • Anticoagulant contamination
      • Consider repeat if questionable
      1. ◆
        Decision

        Pattern of Abnormality

        PT, PTT, or both

        • Isolated prolonged PT
        • Isolated prolonged PTT
        • Both PT and PTT prolonged
        • Thrombin time if needed
        1. ●
          Action

          Isolated PT Prolongation

          Extrinsic pathway

          • Factor VII deficiency (early, short half-life)
          • Warfarin therapy
          • Liver disease (early)
          • Vitamin K deficiency (early)
          • Consider mixing study if unexpected
          1. ◆
            Decision

            Mixing Study

            Mix 1:1 with normal plasma

            • Corrects: Factor deficiency
            • Does not correct: Inhibitor present
            • Partial correction: Weak inhibitor or low factor
            • Incubate for lupus anticoagulant
            1. ●
              Action

              Mixing Study Corrects

              Factor deficiency

              • Order factor assays based on pattern
              • PTT only: VIII, IX, XI, XII
              • PT only: VII
              • Both: II, V, X, fibrinogen
              • Consider von Willebrand panel
              1. ✓
                Outcome

                Final Interpretation

                Diagnosis with clinical correlation

            2. ●
              Action

              Mixing Study Does Not Correct

              Inhibitor present

              • Immediate non-correction: Lupus anticoagulant
              • Time-dependent: Factor VIII inhibitor
              • LA testing: dRVVT, hexagonal phase
              • Bethesda assay for factor inhibitors
              • Consider heparin contamination
              1. ●
                Action

                Lupus Anticoagulant Workup

                ISTH criteria

                • Screen: dRVVT, sensitive aPTT
                • Mixing study: No correction
                • Confirm: Correction with phospholipid
                • Must confirm on 2 occasions 12 weeks apart
                • Associated with thrombosis, not bleeding
        2. ●
          Action

          Isolated PTT Prolongation

          Intrinsic pathway

          • Heparin effect most common
          • Factor VIII, IX, XI, XII deficiency
          • Lupus anticoagulant
          • von Willebrand disease
          • Contact factor deficiency
        3. ●
          Action

          Both PT & PTT Prolonged

          Common pathway or multiple defects

          • DIC (consumptive)
          • Liver disease (advanced)
          • Vitamin K deficiency (advanced)
          • Factor II, V, X deficiency
          • Massive transfusion
          • Anticoagulant overdose

Guideline Source

ISTH Guidelines for Coagulation Testing

DOI: 10.1111/jth.14214View Guideline

Clinical Safety Information

Clinical Decision Support — Not a Substitute for Clinical Judgment

Individual patient factors may require deviation from these recommendations.

Known Limitations

  • Pre-analytical variables affect results
  • Anticoagulant interference must be considered
  • Some rare deficiencies need specialized testing
  • Platelet function testing varies by institution
  • Mixing studies interpretation requires experience

Applicable Regions

USAUUKEU

AU: RCPA haemostasis guidelines

UK: BCSH coagulation testing standards

US: ISTH and CAP guidelines

Version 1Next review: 2028-01-01

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Frequently Asked Questions

What is the Coagulation Disorder Workup Algorithm (ISTH)?

The Coagulation Disorder Workup Algorithm (ISTH) is a diagnostic clinical algorithm for Pathology. It provides a structured decision tree to guide clinical decision-making, based on ISTH Guidelines for Coagulation Testing.

What guideline is the Coagulation Disorder Workup Algorithm (ISTH) based on?

This algorithm is based on ISTH Guidelines for Coagulation Testing (DOI: 10.1111/jth.14214).

What are the limitations of the Coagulation Disorder Workup Algorithm (ISTH)?

Known limitations include: Pre-analytical variables affect results; Anticoagulant interference must be considered; Some rare deficiencies need specialized testing; Platelet function testing varies by institution; Mixing studies interpretation requires experience. Individual patient factors may require deviation from these recommendations.

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