What questions should I ask a patient with a confirmed lower‑extremity deep vein thrombosis before initiating anticoagulation?

Pre-Anticoagulation Assessment for Confirmed Lower Extremity DVT

Before initiating anticoagulation in a patient with confirmed lower extremity DVT, you must systematically assess bleeding risk, renal function, pregnancy status, and any contraindications to anticoagulation. 1, 2

Absolute Contraindications to Anticoagulation

Ask specifically about these conditions that would prevent immediate anticoagulation:

• Active major bleeding (gastrointestinal bleeding, intracranial hemorrhage, gross hematuria requiring transfusion) 2
• Recent CNS bleeding or neurosurgery (within past 4 weeks, including spinal surgery—carries risk of epidural hematoma and permanent neurological injury) 2
• Severe thrombocytopenia (platelet count <50,000/μL typically contraindicates full anticoagulation)
• Recent major surgery within past month, particularly spine, brain, or eye surgery 2

If any absolute contraindication exists, consider IVC filter placement instead of anticoagulation. 1

Bleeding Risk Assessment

Inquire about factors that increase hemorrhagic complications:

• History of major bleeding episodes (prior GI bleed, intracranial hemorrhage, requiring hospitalization or transfusion) 1
• Recent trauma or falls (within past 2-4 weeks)
• Active peptic ulcer disease or known GI lesions (angiodysplasia, varices, inflammatory bowel disease) 3
• Uncontrolled hypertension (systolic BP >180 mmHg or diastolic >110 mmHg)
• Liver disease with coagulopathy (cirrhosis, elevated INR at baseline)
• Concurrent antiplatelet therapy (aspirin, clopidogrel, NSAIDs—increases bleeding risk when combined with anticoagulation)

Renal Function Assessment

Renal impairment critically affects anticoagulant selection and dosing: 4, 3

• Obtain serum creatinine and calculate creatinine clearance (CrCl using Cockcroft-Gault equation) 4
• If CrCl <30 mL/min: Avoid DOACs (rivaroxaban, apixaban, edoxaban, dabigatran) and fondaparinux; use unfractionated heparin (UFH) as it does not require renal clearance 4
• If CrCl 30-50 mL/min: DOACs require dose reduction; LMWH requires dose adjustment or monitoring of anti-Xa levels 4, 3
• If acute kidney injury is present: UFH is the optimal choice because it allows precise dose adjustment with aPTT monitoring and does not accumulate 4

Pregnancy and Reproductive Status

• Is the patient pregnant or potentially pregnant? (Obtain pregnancy test in women of childbearing age) 3
• DOACs and warfarin are contraindicated in pregnancy—LMWH is the anticoagulant of choice throughout pregnancy 3
• Is the patient breastfeeding? (Affects anticoagulant selection)

Cancer History

Active malignancy significantly impacts treatment selection and duration: 1, 5

• Does the patient have active cancer? (Currently receiving chemotherapy, radiation, or diagnosed within past 6 months)
• Type and stage of cancer (particularly important for gastrointestinal malignancies due to higher bleeding risk with DOACs) 3
• If cancer-associated thrombosis: LMWH is preferred over DOACs or warfarin for at least 3 months, with extended anticoagulation as long as cancer remains active 1, 5

Medication History

Document all medications that interact with anticoagulants or increase bleeding risk:

• Current anticoagulants or antiplatelets (aspirin, clopidogrel, prasugrel, ticagrelor, NSAIDs)
• Medications affecting DOAC metabolism (strong CYP3A4 inhibitors like ketoconazole, ritonavir; P-glycoprotein inhibitors/inducers) 3
• Medications affecting warfarin metabolism (antibiotics, antifungals, amiodarone, many others if warfarin is being considered)

Provoked vs. Unprovoked DVT Classification

This determines anticoagulation duration beyond the initial 3 months: 1, 5

• Was there a transient provoking factor? (Surgery, trauma, immobilization >3 days, long-distance travel >8 hours, estrogen therapy, pregnancy within past 3 months) 5, 6
• If provoked by transient risk factor: 3 months of anticoagulation is typically sufficient 1
• If unprovoked (no identifiable trigger): Consider extended anticoagulation beyond 3 months, weighing recurrence risk against bleeding risk 1, 5, 6

DVT Location and Severity

• Is this proximal DVT (popliteal vein or above) or isolated distal DVT? 1
• Proximal DVT requires immediate anticoagulation 1
• Isolated distal DVT without severe symptoms or risk factors for extension: Serial imaging over 2 weeks is an alternative to immediate anticoagulation 1
• Severe symptoms suggesting need for anticoagulation even with distal DVT: Extensive pain, significant swelling, or risk factors for extension (active cancer, prior VTE, inpatient status, extensive clot burden) 1

Prior VTE History

• Has the patient had prior DVT or PE? (Increases recurrence risk and may warrant extended anticoagulation) 5, 6
• If prior VTE, was the patient on anticoagulation when this DVT occurred? (Suggests anticoagulant failure)
• History of heparin-induced thrombocytopenia (HIT)? (Contraindicates UFH and LMWH; requires fondaparinux or direct thrombin inhibitor) 1

Logistical and Social Factors

• Can the patient afford the prescribed anticoagulant? (DOACs are expensive; warfarin requires frequent monitoring but is inexpensive) 3
• Is the patient able to comply with INR monitoring if warfarin is chosen? (Requires regular lab visits)
• Does the patient have reliable access to follow-up care? 1
• Home circumstances adequate for outpatient management? (Most DVT patients can be treated at home unless severe symptoms, high bleeding risk, or inadequate home support) 1

Thrombophilia Screening Considerations

Routine thrombophilia testing is NOT indicated for most patients, but consider in specific scenarios: 7

• First unprovoked VTE at age <50 years
• Recurrent unprovoked VTE
• VTE in unusual locations (cerebral, mesenteric, portal veins)
• Strong family history of VTE (multiple first-degree relatives)
• Warfarin-induced skin necrosis (suggests protein C or S deficiency)

Note that thrombophilia results rarely change acute management decisions and testing should be deferred until after acute treatment phase. 7

Common Pitfalls to Avoid

• Do not delay anticoagulation while awaiting thrombophilia results—these tests do not alter acute management 7
• Do not use LMWH without dose adjustment in severe renal impairment (CrCl <30 mL/min)—accumulation significantly increases bleeding risk 4
• Do not start warfarin before confirming DVT on definitive imaging—warfarin takes days to become therapeutic and initially creates a prothrombotic state 4
• Do not prescribe DOACs in pregnancy—they cross the placenta and are teratogenic 3
• Do not overlook recent spinal surgery as a contraindication—epidural hematoma risk persists for 4 weeks post-operatively 2