Causes of a prolonged prothrombin time (PT) and/or a prolonged activated partial thromboplastin time (aPTT)

Test result		Causes of test result pattern
PT	aPTT	Causes of test result pattern
Prolonged	Normal	Inherited
		Factor VII deficiency
		Acquired
		Mild vitamin K deficiency
		Liver disease
		Warfarin*
		DIC
Normal	Prolonged	Inherited
		Deficiency of factor VIII, IX, or XI
		Deficiency of factor XII, prekallikrein, or HMW kininogen (not associated with a bleeding diathesis)
		von Willebrand disease (variable)
		Acquired
		Heparin, dabigatran, argatroban, direct factor Xa inhibitors (variable)*
		Acquired inhibitor of factor VIII, IX, XI, or XII
		Acquired von Willebrand syndrome
		Lupus anticoagulant (more likely to be associated with thrombosis than bleeding)
Prolonged	Prolonged	Inherited
		Deficiency of prothrombin, fibrinogen, factor V, or factor X
		Combined factor deficiencies
		Acquired
		Liver disease
		DIC
		Severe vitamin K deficiency
		Anticoagulants (supratherapeutic doses of many anticoagulants, combined heparin and warfarin, direct thrombin inhibitors, anticoagulant rodenticide poisoning)*
		Acquired inhibitor of prothrombin, fibrinogen, factor V, or factor X
		Amyloidosis-associated factor X deficiency

Refer to UpToDate topics on use of coagulation tests and on evaluation of patients with bleeding or specific inherited and acquired conditions for additional details.

PT: prothrombin time; aPTT: activated partial thromboplastin time; DIC: disseminated intravascular coagulation; HMW: high molecular weight.
* In principle, many anticoagulants affect common pathway factors and can prolong both the PT and the aPTT if present at high enough levels. As examples:

Warfarin typically prolongs the PT alone, but at high levels warfarin can prolong both tests.
Heparin typically prolongs the aPTT alone (because PT reagents contain heparin-binding agents that block heparin effect), but at high levels heparin can prolong both tests.
Direct thrombin inhibitors (argatroban, dabigatran) typically prolong both tests, but at low levels dabigatran may not prolong the PT.
Direct factor Xa inhibitors (apixaban, edoxaban, rivaroxaban) can prolong the PT and aPTT, although these effects are variable.

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