Table 1.

VTE risk factor classification

ESC2			ISTH1
RF category	Recurrence risk	Examples	RF category	Recurrence risk or risk of index event	Examples
			VTE provoked by a transient risk factor
Major transient or reversible RF associated with >10-fold increased risk for the index VTE event (compared with patients without the risk factor)	Low recurrence risk* (<3%/y)	Surgery with GA for >30 min	Major transient RF during the 3 mo before diagnosis of VTE	Half the risk of recurrent VTE (compared with if there was no transient risk factor), when the risk factor occurred up to 3 mo before the VTE or RF was associated with >10-fold increased risk of having a first VTE	Surgery with GA for >30 min
		Confined to bed in hospital (only bathroom privileges) for ≥3 days because of an acute illness or acute exacerbation of a chronic illness			Confined to bed in hospital (only bathroom privileges) for ≥3 days because of an acute illness
					Cesarean section
		Trauma with fractures
Transient or reversible factors associated with ≤10-fold increased risk for (index) VTE or	Intermediate recurrence risk (3-8%/y)	Minor surgery (GA for <30 min)	Minor (yet important) transient RF during the 2 mo before diagnosis of VTE	Half the risk of recurrent VTE after stopping anticoagulant therapy (compared with if there was no transient RF), when the RF occurred up to 2 mo before the VTE or RF was associated with a 3- to 10-fold increase in the risk of having a first VTE	Surgery with GA for <30 min
		Admission to hospital for <3 days with an acute illness			Admission to hospital for <3 days with an acute illness
		Estrogen therapy/contraception			Estrogen therapy
		Pregnancy or puerperium			Pregnancy or puerperium
		Confined to bed out of hospital for ≥3 days with an acute illness			Confined to bed out of hospital for ≥3 days with an acute illness
		Leg injury (without fracture) associated with reduced mobility for ≥3 days			Leg injury associated with reduced mobility for at least 3 days
		Long haul flight
Nonmalignant persistent risk factors Or		Inflammatory bowel disease
		Active autoimmune disease
No identifiable risk factor		No identifiable risk factor	Unprovoked VTE
				Recurrence risk individualized/stratified using other assessments†	No provoking factors (transient or persistent)
			VTE provoked by a persistent risk factor
	High recurrence risk (>8%/y)	Active cancer	Active cancer		Cancer is considered active if any of the following apply: (1) has not received potentially curative treatment; or (2) there is evidence that treatment has not been curative (eg, recurrent or progressive disease); or (3) treatment is ongoing
		At least 1 previous episode of VTE in the absence of a major transient or reversible factor
		Antiphospholipid antibody syndrome
			Ongoing nonmalignant condition associated with at least a 2-fold risk of recurrent VTE after stopping anticoagulant therapy		Inflammatory bowel disease.

GA, general anesthesia; RF, risk factor.

^*If anticoagulation is discontinued after the first 3 months.

^†Described in text of guideline and in this current review.