Prothrombin time	Partial thromboplastin time	Further evaluation	Next step
Normal	Normal	Platelet Function Analyzer-100, which checks the amount of time it takes platelets to aggregate onto an aperture coated with a collagen/epinephrine membrane and a collagen/adenosine diphosphate membrane	Is there a prolonged aggregation time with both membranes? Yes: Evaluate for von Willebrand's disease No: If prolonged aggregation time is found only with the collagen/epinephrine membrane, look for drug effect, such as from aspirin. If neither are prolonged, further evaluation is warranted, based on clinical suspicion
Normal	Abnormal	Partial thromboplastin time mixing study	Does partial thromboplastin time correct (normalize)? Yes: Factor VIII, IX, and XI assays. If factor VIII low, work-up for von Willebrand's disease No: Screen for inhibitors (lupus anticoagulant and factor VIII inhibitor)
Abnormal	Normal	Determine if the patient is malnourished or if there is clinical suspicion for vitamin K deficiency	Does prothrombin time correct or normalize with administration of vitamin K? Yes: Replace vitamin K as needed No: Factor assay for factor VII
Abnormal	Abnormal	Consider disseminated intravascular coagulopathy	Consider factor assays for factor deficiencies
		Verify no use of warfarin (Coumadin) or heparin
		Verify no liver disease