🩸 Coagulation Test Interpretation

When to use

Localise a coagulation abnormality to the intrinsic, extrinsic or common pathway and separate deficiency from inhibitor.

How it works

PT = extrinsic/common; aPTT = intrinsic/common. Mixing study: corrects = deficiency, does not correct = inhibitor.

Key points

• Isolated PT rise: VII deficiency, early warfarin/vitamin K deficiency, liver disease.
• Isolated aPTT rise: haemophilia, vWD, heparin, lupus anticoagulant.
• DIC: low fibrinogen, high D-dimer, low platelets, prolonged PT/aPTT.
• Normal PT/aPTT with bleeding: consider platelet/vessel disorder, XIII deficiency, mild vWD.

References

• Standard interpretation of PT/aPTT and the mixing study

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