Thrombus in the deep venous system, most often lower extremity — risk-stratify with Wells, confirm with duplex US, treat with anticoagulation.
Also known as: DVT, deep vein thrombosis, venous thromboembolism, VTE, lower extremity thrombosis
Overview
Formation of thrombus within the deep venous system, most commonly involving lower extremity veins (popliteal, femoral, iliac). Proximal DVT (popliteal or above) carries the highest risk of pulmonary embolism; distal (calf) DVT is generally lower risk.
Epidemiology
Annual incidence of venous thromboembolism ~1-2 per 1000. Together with PE, VTE is the third most common cardiovascular cause of death. Up to half are provoked by identifiable risk factors; the remainder unprovoked.
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Question 1HematologyMedium
A 55-year-old man with multiple myeloma on lenalidomide maintenance develops acute bilateral lower extremity deep vein thrombosis. He has chronic kidney disease stage 3 (eGFR 42 mL/min/1.73 m2). Which of the following is the most appropriate anticoagulation?
AWarfarin
BLow-molecular-weight heparin (LMWH) (enoxaparin)
CFondaparinux
DApixaban
EDabigatran
Reveal answer & full explanation
Correct answer: D — Apixaban
AWarfarin
BLow-molecular-weight heparin (LMWH) (enoxaparin)
CFondaparinux
DApixaban✓
EDabigatran
Why Apixaban is correct
For cancer-associated venous thromboembolism, direct oral anticoagulants (apixaban, rivaroxaban) are preferred over low-molecular-weight heparin for most patients per CHEST 2021 and ASH 2021 guidance (ASCO 2023 lists LMWH and these agents as equally acceptable), with equal or better efficacy and oral dosing.
Apixaban is the least renally cleared direct oral anticoagulant and needs no renal dose adjustment for VTE; the pivotal VTE trial (AMPLIFY) excluded creatinine clearance below 25 mL/min, so data are limited below that, and an eGFR of 42 is within the studied range.
Lenalidomide markedly raises venous thromboembolism risk in myeloma, so full therapeutic anticoagulation is indicated.
Why the others are wrong
Fondaparinux — a once-daily subcutaneous factor Xa inhibitor that is an acceptable alternative to LMWH for initial VTE treatment, but it is cleared entirely by the kidney (caution at creatinine clearance 30-50 mL/min, contraindicated below 30), commits the patient to indefinite injections, and is not a guideline-preferred agent for cancer-associated venous thromboembolism (right-target, wrong-agent trap).
Low-molecular-weight heparin (LMWH) (enoxaparin) — the former standard, still an acceptable guideline option (enoxaparin needs no dose change at creatinine clearance of 30 mL/min or higher), but oral factor Xa inhibitors are now favored for most patients, with LMWH preferred mainly for luminal GI or GU cancers with high bleeding risk; this patient has neither, so daily injections offer no advantage over apixaban (right-idea, outdated-standard trap).
Warfarin — variable INR control and chemotherapy drug interactions make it the least-preferred agent in cancer-associated venous thromboembolism (right-class, wrong-agent trap).
Dabigatran — a direct oral anticoagulant, so it seems interchangeable with apixaban, but it is about 80% renally cleared, requires 5-10 days of parenteral lead-in for VTE, and lacks the cancer-associated venous thromboembolism trial data behind apixaban, rivaroxaban, and edoxaban, so it is not a guideline-preferred agent here (same-class, wrong-agent trap).
Question 2HematologyMedium
A 68-year-old male with a second unprovoked DVT (18 months after completing 6 months of rivaroxaban) has no identifiable precipitant. Which of the following is the most appropriate anticoagulation duration?
ASix months of rivaroxaban
BIndefinite anticoagulation
CIndefinite aspirin 81 mg
DTwelve months of rivaroxaban
EThree months of rivaroxaban
Reveal answer & full explanation
Correct answer: B — Indefinite anticoagulation
ASix months of rivaroxaban
BIndefinite anticoagulation✓
CIndefinite aspirin 81 mg
DTwelve months of rivaroxaban
EThree months of rivaroxaban
Why Indefinite anticoagulation is correct
Recurrent unprovoked venous thromboembolism (VTE): indefinite anticoagulation is recommended per American College of Chest Physicians (ACCP) and American Society of Hematology (ASH) guidelines
Recurrence risk off anticoagulation is high: about 10% in the first year and 30% at 5 years after a first unprovoked VTE, and an estimated 1.5 times higher after a second (about 15% in the first year and 45% at 5 years)
This patient already recurred after a finite course, confirming the need for extended therapy
Why the others are wrong
Three months of rivaroxaban — insufficient duration given the high recurrence risk after a second unprovoked VTE (undertreatment)
Indefinite aspirin 81 mg — aspirin is inferior to anticoagulants for VTE secondary prevention (right-concept-wrong-drug)
Six months of rivaroxaban — also insufficient; this patient already completed 6 months after the first event and still recurred (anchoring on prior course)
Twelve months of rivaroxaban — a longer fixed course feels like a reasonable compromise with bleeding risk, but recurrence risk after a second unprovoked VTE persists and returns once anticoagulation stops, so guidelines recommend extended therapy with no scheduled stop date and periodic reassessment rather than an arbitrary 12-month endpoint (arbitrary finite extension)
Additional high-yield points
Extended-duration low-dose options: apixaban 2.5 mg BID (AMPLIFY-EXT: 80% relative risk reduction vs placebo) or rivaroxaban 10 mg daily (EINSTEIN-CHOICE: superior to aspirin)
Annual risk-benefit reassessment: bleeding risk increases with age and comorbidities
Thrombophilia testing: perform after completing anticoagulation (results are unreliable while on anticoagulants)
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Inherited thrombophilia: Factor V Leiden, prothrombin G20210A, protein C/S/antithrombin deficiency
Antiphospholipid antibody syndrome
Obesity, age >60, smoking
Prior VTE (strongest single risk factor for recurrence)
Central venous catheter, indwelling hardware
Pathophysiology
Stasis in venous valve cusps combined with hypercoagulable state initiates thrombus formation. The thrombus may extend proximally or embolize to the pulmonary circulation. Chronic venous outflow obstruction and valvular damage lead to post-thrombotic syndrome.
Clinical presentation
Symptoms
Unilateral leg swelling and pain (most common)
Calf or thigh discomfort, often worse with walking
Warmth, erythema
Asymptomatic in many cases — first manifestation may be pulmonary embolism
Phlegmasia cerulea dolens (rare, limb-threatening): severe swelling, cyanosis, pain from massive iliofemoral thrombus; often preceded by phlegmasia alba dolens (pale, swollen, painful limb) and can progress to venous gangrene; unlike acute arterial occlusion, the limb is massively swollen and pulses are initially preserved
Signs / physical exam
Unilateral leg swelling >3 cm calf circumference difference (measured 10 cm below tibial tuberosity)
Pitting edema, palpable cord
Erythema, warmth
Homan sign (calf pain with dorsiflexion) — historical, low sensitivity/specificity
Chronic venous insufficiency / superficial thrombophlebitis — Palpable cord along superficial vein; tender erythematous track; duplex to exclude concurrent DVT (found in up to a quarter); SVT can propagate into the deep veins causing DVT/PE, so SVT ≥5 cm gets prophylactic-dose fondaparinux 2.5 mg SC daily × 45 days and SVT within 3 cm of the saphenofemoral junction is treated as DVT with therapeutic anticoagulation; short distal SVT: NSAIDs and warm compresses
Lymphedema — Chronic non-pitting edema with skin changes; bilateral or asymmetric without acute pain
Compartment syndrome — Pain out of proportion, paresthesia, post-trauma or post-exercise; emergent surgical consult
Wells DVT score: each +1 for active cancer, paralysis/immobilization, recent surgery, localized tenderness along deep veins, entire leg swelling, calf >3 cm difference, pitting edema, collateral superficial veins, prior DVT; subtract 2 if alternative diagnosis as likely. Score ≥2 = likely; <2 = unlikely. Unlikely + negative D-dimer rules out; likely or positive D-dimer warrants duplex.
Labs
D-dimer — sensitive but nonspecific; useful in low-pretest-probability patients to exclude DVT
CBC, BMP, coagulation studies, hepatic function (drug dosing)
Pregnancy test in women of childbearing age
Selective thrombophilia workup (Factor V Leiden, prothrombin G20210A, protein C/S, antithrombin, antiphospholipid antibodies) — in young unprovoked DVT, recurrent VTE, or strong family history; defer testing until off anticoagulation when possible
Age-appropriate cancer screening for unprovoked VTE — no aggressive occult malignancy workup unless symptoms or signs
Imaging
Compression duplex ultrasound — first-line; sensitivity and specificity >95% for proximal DVT
CT or MR venography for proximal pelvic veins or IVC when duplex limited
Echocardiography and CTPA if PE suspected concurrently
Wells criteria for clinical pretest probability — drives D-dimer vs imaging decision
Diagnostic algorithm
flowchart TD
A[Suspected DVT] --> B[Wells DVT score]
B --> C{Score}
C -->|Unlikely <2| D[D-dimer]
D --> E{D-dimer<br/>elevated?}
E -->|No| F[DVT excluded]
E -->|Yes| G[Compression duplex US]
C -->|Likely ≥2| G
G --> H{Thrombus<br/>identified?}
H -->|No| I[Consider alternate dx<br/>or repeat US in 5-7 days<br/>if high suspicion]
H -->|Yes| J["Anticoagulate: DOAC preferred, incl. most cancer VTE<br/>LMWH for pregnancy or GI/GU cancer with bleeding risk<br/>Warfarin if specific indication"]
J --> K{Provoked vs<br/>unprovoked?}
K -->|Provoked| L[3 months therapy]
K -->|Unprovoked / recurrent /<br/>persistent risk| M[Consider indefinite therapy<br/>based on bleeding risk]
Diagnostic and treatment algorithm for suspected lower extremity DVT.
Treatment
First-line
Anticoagulation — direct oral anticoagulants (DOACs) preferred for most acute VTE in absence of contraindications:
• Apixaban 10 mg PO BID × 7 days then 5 mg BID
• Rivaroxaban 15 mg PO BID × 21 days then 20 mg daily with food
• Edoxaban — requires 5-10 day bridge with parenteral anticoagulation first
• Dabigatran — requires 5-10 day bridge with parenteral anticoagulation first
Low-molecular-weight heparin (enoxaparin 1 mg/kg SC q12h) — preferred in pregnancy; postpartum and breastfeeding: LMWH or warfarin (both compatible with breastfeeding), avoid DOACs, and continue at least 6 weeks postpartum and at least 3 months in total; cancer-associated VTE: an oral Xa inhibitor (apixaban, edoxaban, rivaroxaban) is first-line, with LMWH favored for luminal GI/GU cancers at high bleeding risk or with major drug interactions; severe renal impairment (CrCl <30): IV unfractionated heparin rather than LMWH, which accumulates
Warfarin with parenteral bridging (target INR 2-3) — for patients on warfarin already, mechanical heart valves, certain APS, or DOAC intolerance
Duration: 3 months minimum for provoked DVT; indefinite for unprovoked proximal DVT or PE with low bleeding risk, recurrent VTE, or persistent risk factor
Second-line / adjunct
IVC filter — only for acute VTE with absolute contraindication to anticoagulation, or recurrent VTE despite therapeutic anticoagulation; retrievable filters preferred and should be removed when anticoagulation can resume
Catheter-directed thrombolysis or thrombectomy — for limb-threatening iliofemoral DVT (phlegmasia); may be considered in selected younger patients with acute iliofemoral DVT and low bleeding risk, but not routine for proximal DVT since the ATTRACT trial showed no overall reduction in post-thrombotic syndrome and more major bleeding
Compression stockings (20-30 mmHg) for symptomatic relief; routine use no longer recommended solely to prevent post-thrombotic syndrome (SOX trial)
Wells score with negative D-dimer reliably rules out DVT in low-risk outpatients — saves imaging.
DOACs are first-line for most VTE, including most cancer-associated VTE; LMWH is still preferred in pregnancy and luminal GI/GU cancers with high bleeding risk.
Unprovoked proximal DVT or PE → consider indefinite anticoagulation given high recurrence risk.
Stop estrogen-containing contraceptives in any patient diagnosed with VTE on hormonal therapy.
IVC filters are reserved for those who CANNOT be anticoagulated — they do not replace anticoagulation when it can be given.
Mechanisms: apixaban, rivaroxaban, and edoxaban directly inhibit factor Xa; dabigatran and argatroban directly inhibit thrombin; UFH, LMWH, and fondaparinux act indirectly by potentiating antithrombin (UFH inhibits both thrombin and Xa, LMWH and fondaparinux mainly Xa); warfarin is a vitamin K antagonist that blocks synthesis of factors II, VII, IX, and X.
References
CHEST 2021 VTE — Antithrombotic Therapy for VTE Disease: Second Update of the CHEST Guideline and Expert Panel Report (Stevens et al., Chest 2021)
ASH 2020 VTE — American Society of Hematology 2020 Guidelines for Management of Venous Thromboembolism (Ortel et al., Blood Adv 2020)
AMPLIFY — Oral Apixaban for the Treatment of Acute Venous Thromboembolism (Agnelli et al., NEJM 2013)
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