Wells' Criteria for Deep Vein Thrombosis (DVT)

Comprehensive guide to Wells' Criteria for DVT: clinical prediction rule, scoring system, probability stratification, diagnostic algorithm integration, and evidence-based management for deep vein thrombosis assessment.

Wells' Criteria for DVT Calculator

Wells' Criteria for Deep Vein Thrombosis

Select all criteria that apply to the patient. Each criterion has a specific point value. The alternative diagnosis criterion subtracts 2 points.

Active cancer (treatment ongoing, within 6 months, or palliative)

+1 point

Paralysis, paresis, or recent plaster immobilization of the lower extremities

+1 point

Recently bedridden for more than 3 days or major surgery within 12 weeks

+1 point

Localized tenderness along the distribution of the deep venous system

+1 point

Entire leg swollen

+1 point

Calf swelling by more than 3 cm compared to the asymptomatic leg (measured 10 cm below the tibial tuberosity)

+1 point

Pitting edema confined to the symptomatic leg

+1 point

Collateral superficial veins (non-varicose)

+1 point

Alternative diagnosis as likely or more likely than DVT

-2 points

Disclaimer: This calculator is for educational purposes only and should not replace clinical judgment. Wells' Criteria is a clinical prediction rule and should be used in conjunction with other clinical findings, laboratory tests, and imaging studies. Always consult with a healthcare professional for medical decisions.

Wells' Criteria for DVT Explained

Wells' Criteria for Deep Vein Thrombosis

Wells' Criteria is a clinical prediction rule used to assess the probability of deep vein thrombosis (DVT) in patients presenting with symptoms suggestive of DVT. It helps guide clinical decision-making regarding the need for further diagnostic testing, such as D-dimer testing and compression ultrasound.

Scoring System:

• < 1 point: Low probability of DVT
• 1-2 points: Moderate probability of DVT
• ≥ 3 points: High probability of DVT

Detailed Criteria and Point Values

Positive Criteria (+1 point each)

Active cancer (+1 point)

Cancer treatment ongoing, within the previous 6 months, or receiving palliative care. This includes any active malignancy regardless of type or stage.

Paralysis, paresis, or recent plaster immobilization (+1 point)

Paralysis or paresis of the lower extremities, or recent plaster cast immobilization of the lower leg. This includes stroke-related paralysis, spinal cord injury, or orthopedic immobilization.

Recently bedridden or major surgery (+1 point)

Recently bedridden for more than 3 days (within the past 4 weeks) or major surgery within the past 12 weeks. Major surgery includes procedures requiring general anesthesia.

Localized tenderness (+1 point)

Localized tenderness along the distribution of the deep venous system. This is typically assessed by palpating along the course of the deep veins (femoral, popliteal, posterior tibial).

Entire leg swollen (+1 point)

The entire leg (from thigh to ankle) is swollen, not just a localized area. Compare with the asymptomatic leg.

Calf swelling >3 cm (+1 point)

Calf swelling by more than 3 cm compared to the asymptomatic leg, measured 10 cm below the tibial tuberosity. This is a quantitative measurement requiring careful comparison.

Pitting edema (+1 point)

Pitting edema confined to the symptomatic leg. Pitting edema is assessed by applying firm pressure to the skin and observing if an indentation remains after release.

Collateral superficial veins (+1 point)

Collateral superficial veins (non-varicose) visible on the affected leg. These are dilated superficial veins that develop as collateral circulation when deep veins are obstructed.

Negative Criterion (-2 points)

Alternative diagnosis as likely or more likely (-2 points)

An alternative diagnosis is considered as likely or more likely than DVT based on clinical assessment. Common alternative diagnoses include:

• Cellulitis
• Muscle strain or injury
• Baker's cyst
• Superficial thrombophlebitis
• Venous insufficiency
• Lymphedema
• Post-thrombotic syndrome
• Trauma or hematoma

This is the only criterion that subtracts points, reflecting that if another diagnosis is more likely, the probability of DVT decreases.

Clinical Application

When to Use Wells' Criteria

Patient presenting with symptoms suggestive of DVT (leg swelling, pain, tenderness)
Assessment of DVT probability before ordering diagnostic tests
Guiding decision-making regarding D-dimer testing and imaging
Risk stratification for DVT in clinical practice
Emergency department and outpatient evaluation
Post-operative and hospitalized patient assessment

How to Use Wells' Criteria

Assess Clinical Features: Evaluate the patient for all 9 criteria systematically.
Calculate Score: Add 1 point for each positive criterion present, subtract 2 points if alternative diagnosis is likely.
Determine Probability: Classify as low (<1), moderate (1-2), or high (≥3) probability.
Guide Testing: Use the probability to determine next steps:
- • Low probability: Consider D-dimer; if negative, DVT unlikely
- • Moderate probability: D-dimer recommended; if positive, proceed to imaging
- • High probability: Proceed directly to compression ultrasound
Clinical Correlation: Always correlate with clinical judgment and patient presentation.

Score Interpretation and Management

Low Probability (< 1 point)

Interpretation: DVT is unlikely based on clinical criteria.

Recommended Testing:

• D-dimer testing can be considered
• If D-dimer negative: DVT unlikely, consider alternative diagnoses
• If D-dimer positive: Consider compression ultrasound

Management: Consider alternative diagnoses. Clinical follow-up recommended.

Moderate Probability (1-2 points)

Interpretation: Moderate probability of DVT. Further testing recommended.

Recommended Testing:

• D-dimer testing recommended
• If D-dimer positive: Proceed to compression ultrasound
• If D-dimer negative: DVT unlikely (consider other diagnoses)

Management: Close clinical monitoring. Consider anticoagulation if imaging confirms DVT.

High Probability (≥ 3 points)

Interpretation: High probability of DVT. Imaging required.

Recommended Testing:

• Compression ultrasound (preferred imaging modality)
• D-dimer testing not necessary (proceed directly to imaging)
• Consider empiric anticoagulation while awaiting imaging

Management: Urgent imaging required. If DVT confirmed, initiate anticoagulation therapy. Consider risk factors for bleeding before anticoagulation.

Key Clinical Features

Compression Ultrasound

The gold standard imaging test for DVT diagnosis. Non-compressible veins indicate thrombosis. Preferred over venography due to non-invasiveness and availability.

D-dimer Testing

Highly sensitive but not specific for DVT. Useful for ruling out DVT when negative in low-moderate probability patients. Positive D-dimer requires further imaging.

Risk Factors

Common risk factors include immobility, surgery, cancer, previous VTE, pregnancy, oral contraceptives, and inherited thrombophilias. These factors increase DVT probability.

Complications

Untreated DVT can lead to pulmonary embolism (PE), post-thrombotic syndrome, and chronic venous insufficiency. Early diagnosis and treatment are crucial to prevent complications.

Pathophysiology

Virchow's Triad

DVT formation is explained by Virchow's Triad, which includes three factors:

Venous stasis: Immobility, paralysis, or reduced blood flow
Endothelial injury: Trauma, surgery, or inflammation
Hypercoagulability: Cancer, inherited thrombophilias, pregnancy, or medications

When one or more of these factors are present, the risk of DVT increases. Wells' Criteria helps identify patients with these risk factors and clinical features suggestive of DVT.

Why This Scoring System?

Wells' Criteria combines multiple clinical features and risk factors into a single score that correlates with DVT probability. The scoring system:

Standardizes DVT probability assessment
Reduces unnecessary imaging in low-probability patients
Ensures high-probability patients receive appropriate testing
Guides efficient use of healthcare resources
Improves diagnostic accuracy when combined with D-dimer and imaging

Important Limitations

• Wells' Criteria is a clinical prediction rule and should not be used in isolation
• Requires clinical judgment and experience in assessment
• Should be interpreted in the context of complete clinical picture
• Requires correlation with patient history, physical examination, and diagnostic tests
• Inter-observer variability may exist in scoring
• Not a substitute for clinical judgment or comprehensive evaluation
• Consider other causes of leg symptoms (cellulitis, muscle injury, etc.)
• May have reduced accuracy in certain populations (e.g., recurrent DVT, post-thrombotic syndrome)
• Always consider patient-specific factors and comorbidities
• Treatment decisions should be based on multiple factors, not just the score
• D-dimer testing and imaging remain essential components of DVT diagnosis
• Clinical follow-up is important even with low probability scores if symptoms persist

Deep vein thrombosis (DVT) represents a significant clinical challenge, with an estimated annual incidence of 1-2 cases per 1,000 individuals in the general population. The condition carries substantial morbidity and mortality risks, particularly through its most feared complication: pulmonary embolism (PE). Early and accurate diagnosis is paramount, yet the clinical presentation of DVT can be subtle, nonspecific, or entirely asymptomatic in up to 50% of cases. This diagnostic uncertainty has driven the development of clinical prediction rules designed to stratify patients by their probability of having DVT, thereby optimizing the use of diagnostic resources while ensuring appropriate care.

Wells' Criteria for DVT, first published by Dr. Philip Wells and colleagues in 1997, emerged as a response to the need for a standardized, evidence-based approach to DVT probability assessment. The criteria were developed through systematic evaluation of clinical features and risk factors that could reliably distinguish patients with DVT from those without. Over the subsequent decades, Wells' Criteria has become one of the most widely validated and utilized clinical prediction rules in emergency medicine, internal medicine, and vascular medicine practice.

Historical Development and Validation

The original Wells' Criteria study involved a cohort of 529 consecutive patients presenting to emergency departments and outpatient clinics with suspected DVT. Through multivariate analysis, the researchers identified nine clinical features that independently predicted the presence of DVT. These features were weighted based on their predictive strength, with some criteria assigned positive points and one criterion (alternative diagnosis) assigned negative points to reflect its protective effect against DVT diagnosis.

Subsequent validation studies have consistently demonstrated the reliability of Wells' Criteria across diverse patient populations and clinical settings. The criteria have been validated in emergency departments, primary care settings, inpatient wards, and specialized thrombosis clinics. Meta-analyses have confirmed the criteria's utility, with pooled sensitivity and specificity values that support their clinical application. The widespread adoption of Wells' Criteria has been facilitated by its simplicity, reproducibility, and integration into clinical practice guidelines from major medical societies worldwide.

Pathophysiology and Virchow's Triad

Understanding the pathophysiology of DVT provides essential context for interpreting Wells' Criteria. The formation of venous thrombosis follows the principles of Virchow's Triad, a conceptual framework describing three fundamental factors that predispose to thrombosis: venous stasis, endothelial injury, and hypercoagulability.

Venous Stasis: Reduced blood flow in the venous system creates conditions favorable for thrombus formation. Immobility, whether from bed rest, paralysis, or prolonged sitting, allows blood to pool in the deep veins of the lower extremities. The calf muscle pump, which normally facilitates venous return during ambulation, becomes ineffective during periods of immobility. This stasis permits local accumulation of activated clotting factors and platelets, initiating the thrombotic cascade.

Endothelial Injury: Damage to the vascular endothelium exposes subendothelial collagen and tissue factor, triggering platelet adhesion and activation of the coagulation cascade. Endothelial injury can result from direct trauma, surgical manipulation, inflammation, or the presence of indwelling catheters. The injured endothelium also loses its natural anticoagulant properties, further promoting thrombosis.

Hypercoagulability: An imbalance in the coagulation system favoring clot formation characterizes hypercoagulable states. These can be inherited, such as factor V Leiden mutation or prothrombin gene mutation, or acquired, including malignancy, pregnancy, oral contraceptive use, or inflammatory conditions. The presence of multiple hypercoagulable factors significantly increases DVT risk, which is reflected in Wells' Criteria through the active cancer criterion.

The interaction of these three factors creates a permissive environment for DVT formation. Wells' Criteria effectively captures clinical manifestations and risk factors associated with each component of Virchow's Triad, making it a physiologically grounded prediction tool.

Detailed Criteria Analysis

Active Cancer (1 point)

Malignancy represents one of the strongest independent risk factors for venous thromboembolism (VTE), with cancer patients experiencing a 4-7 fold increased risk compared to the general population. The association between cancer and thrombosis is multifactorial, involving tumor-derived procoagulant substances, chemotherapy-induced endothelial damage, immobility, and the hypercoagulable state associated with malignancy. Wells' Criteria assigns 1 point for active cancer, defined as treatment ongoing, within the previous 6 months, or palliative care. This broad definition captures patients across the spectrum of cancer care, recognizing that thrombotic risk persists beyond active treatment periods.

The relationship between cancer type and thrombosis risk varies, with adenocarcinomas, particularly pancreatic, gastric, and brain tumors, demonstrating the highest rates of VTE. However, Wells' Criteria appropriately does not distinguish between cancer types, as the clinical prediction rule aims for simplicity and broad applicability. The cancer criterion has demonstrated strong predictive value, with cancer patients in the original validation study showing significantly higher DVT prevalence.

Paralysis, Paresis, or Recent Plaster Immobilization (1 point)

Neurological impairment or orthopedic immobilization of the lower extremities creates conditions of profound venous stasis. Paralysis eliminates the calf muscle pump mechanism entirely, while paresis significantly reduces its effectiveness. Plaster cast immobilization similarly restricts muscle contraction and joint movement, leading to stasis in the immobilized limb.

This criterion reflects the well-established association between immobility and DVT risk. Patients with stroke-related hemiparesis, spinal cord injury, or lower extremity fractures demonstrate substantially elevated DVT rates. The criterion's inclusion recognizes that these conditions represent high-risk scenarios requiring careful clinical evaluation, even in the absence of classic DVT symptoms.

Recently Bedridden or Major Surgery (1 point)

Prolonged bed rest, defined as more than 3 days within the past 4 weeks, or major surgery within the past 12 weeks, represents another manifestation of venous stasis. The temporal windows specified in Wells' Criteria reflect the period of highest thrombotic risk following these events. Major surgery, particularly orthopedic procedures involving the lower extremities or pelvis, abdominal surgery, and neurosurgery, carries especially high DVT risk due to the combination of immobility, tissue trauma, and inflammatory responses.

The 12-week window for major surgery recognizes that thrombotic risk remains elevated for several months postoperatively, even after patients have resumed ambulation. This extended risk period reflects the gradual resolution of surgery-induced hypercoagulability and the potential for delayed presentation of perioperative thromboses.

Localized Tenderness Along Deep Venous System (1 point)

Physical examination findings that suggest venous inflammation or thrombosis contribute to the clinical assessment. Localized tenderness along the distribution of the deep venous system—specifically the femoral, popliteal, and posterior tibial veins—can indicate thrombophlebitis or perivenous inflammation. This finding requires careful palpation along the anatomical course of the deep veins, distinguishing it from superficial tenderness related to other causes.

The specificity of this finding for DVT is moderate, as tenderness can result from various conditions including muscle injury, cellulitis, or superficial thrombophlebitis. However, when present in conjunction with other Wells' Criteria, localized tenderness increases the overall probability of DVT. The criterion emphasizes the importance of systematic physical examination in DVT evaluation.

Entire Leg Swollen (1 point)

Diffuse leg swelling involving the entire lower extremity, from thigh to ankle, suggests extensive venous obstruction or systemic factors affecting venous return. This finding differs from localized swelling, which might indicate other pathologies. The criterion requires comparison with the contralateral leg, as bilateral swelling suggests systemic causes such as heart failure, renal disease, or bilateral DVT.

Unilateral entire leg swelling in the context of suspected DVT is particularly concerning, as it may indicate proximal (iliofemoral) thrombosis, which carries higher embolic risk than isolated calf DVT. This finding has demonstrated good inter-observer reliability and contributes meaningfully to the overall Wells' score.

Calf Swelling Greater Than 3 cm (1 point)

Quantitative measurement of calf circumference provides an objective assessment of swelling. The criterion specifies measurement 10 cm below the tibial tuberosity, ensuring standardization. A difference of more than 3 cm between the symptomatic and asymptomatic legs represents significant asymmetry, suggesting localized pathology.

This quantitative approach enhances the reliability of the clinical assessment, as subjective impressions of swelling can vary between examiners. The 3 cm threshold was selected based on its optimal balance between sensitivity and specificity in the original validation study. Measurement technique is important: the tape measure should be perpendicular to the long axis of the leg, and measurements should be taken at the same anatomical level on both legs.

Pitting Edema Confined to Symptomatic Leg (1 point)

Pitting edema, characterized by persistent indentation after application of firm pressure, indicates increased interstitial fluid accumulation. When confined to the symptomatic leg, pitting edema suggests localized venous obstruction or inflammation. The finding is assessed by applying firm pressure (typically with the thumb) to the pretibial area or medial malleolus for 5 seconds, then observing whether an indentation remains after release.

The specificity of pitting edema for DVT is enhanced when it is unilateral and confined to the symptomatic leg. Bilateral pitting edema suggests systemic causes such as heart failure, liver disease, or renal dysfunction. The criterion's emphasis on confinement to the symptomatic leg helps distinguish DVT-related edema from other causes.

Collateral Superficial Veins (1 point)

Dilated superficial veins, visible as collateral circulation, develop when deep venous obstruction forces blood to reroute through superficial pathways. These collateral veins are non-varicose, distinguishing them from primary varicose veins. The presence of prominent collateral veins suggests chronic or significant deep venous obstruction, though acute DVT can also produce this finding if pre-existing venous insufficiency is present.

This criterion requires visual inspection of the leg, looking for prominent, dilated superficial veins that are not typical varicosities. The finding is more common in patients with extensive proximal DVT or those with underlying chronic venous insufficiency. While less common than other criteria, its presence significantly increases DVT probability.

Alternative Diagnosis as Likely or More Likely (-2 points)

This unique negative criterion reflects the importance of clinical reasoning in DVT assessment. When an alternative diagnosis adequately explains the patient's symptoms and appears as likely or more likely than DVT, the probability of DVT decreases. Common alternative diagnoses include cellulitis, muscle strain or injury, Baker's cyst, superficial thrombophlebitis, venous insufficiency, lymphedema, post-thrombotic syndrome, trauma, or hematoma.

The -2 point value reflects that a compelling alternative diagnosis substantially reduces DVT probability. This criterion emphasizes that Wells' Criteria should not be applied mechanistically but requires integration with clinical judgment. The presence of a clear alternative diagnosis, particularly one that explains all the patient's symptoms, should prompt consideration of that diagnosis before pursuing extensive DVT evaluation.

Scoring System and Probability Stratification

Wells' Criteria produces a score ranging from -2 to +9, though in practice, scores typically range from -2 to +8. The scoring system stratifies patients into three probability categories:

Low Probability (< 1 point): Patients scoring less than 1 point have a low probability of DVT, with prevalence rates typically ranging from 3-5% in validation studies. This low prevalence suggests that extensive diagnostic testing may not be necessary, particularly if D-dimer testing is available. A negative D-dimer in a low-probability patient effectively rules out DVT, with negative predictive values exceeding 99%.

Moderate Probability (1-2 points): Patients in this category have intermediate DVT prevalence, typically 17-33% depending on the study population. These patients require further diagnostic evaluation, usually beginning with D-dimer testing. A positive D-dimer in moderate-probability patients should prompt compression ultrasound, while a negative D-dimer effectively rules out DVT in most cases.

High Probability (≥ 3 points): High-probability patients demonstrate DVT prevalence rates of 75-85% in validation studies. These patients should proceed directly to compression ultrasound, as D-dimer testing adds little value given the high pre-test probability. Some guidelines suggest considering empiric anticoagulation while awaiting imaging in high-probability patients, though this must be balanced against bleeding risk.

Integration with Diagnostic Testing

Wells' Criteria functions optimally when integrated into a diagnostic algorithm that incorporates D-dimer testing and compression ultrasound. The criteria help determine the appropriate sequence and necessity of these tests, optimizing resource utilization while maintaining diagnostic accuracy.

D-dimer Testing

D-dimer, a fibrin degradation product, is highly sensitive for VTE but lacks specificity, as elevated levels occur in numerous conditions including infection, inflammation, malignancy, pregnancy, and recent surgery. The high sensitivity (typically 95-97%) makes D-dimer valuable for ruling out DVT when negative, particularly in low and moderate probability patients.

In low-probability patients with negative D-dimer, DVT can be effectively ruled out without imaging. In moderate-probability patients, negative D-dimer similarly rules out DVT, while positive D-dimer requires compression ultrasound. High-probability patients should proceed directly to imaging, as D-dimer testing provides little additional information given the high pre-test probability.

Compression Ultrasound

Compression ultrasound represents the imaging modality of choice for DVT diagnosis. The test involves applying pressure with the ultrasound probe to compress the deep veins. Non-compressible veins indicate the presence of thrombus. The test is highly sensitive (95-98%) and specific (96-98%) for proximal DVT, though sensitivity is lower (60-70%) for isolated calf DVT.

Wells' Criteria helps determine when compression ultrasound is necessary. High-probability patients require immediate imaging. Moderate-probability patients with positive D-dimer require imaging. Low-probability patients typically do not require imaging unless D-dimer is positive or clinical suspicion persists despite negative D-dimer.

Clinical Application and Decision-Making

The practical application of Wells' Criteria requires systematic assessment of all nine criteria, careful calculation of the score, and integration of the result into a diagnostic and management plan. The criteria should be applied to all patients presenting with symptoms or signs suggestive of DVT, including leg swelling, pain, tenderness, warmth, or erythema.

Clinical judgment remains essential when applying Wells' Criteria. The criteria should not be used in isolation but rather as one component of a comprehensive clinical assessment. Factors not captured by Wells' Criteria, such as patient age, comorbidities, medication use, and family history, may influence clinical decision-making. Additionally, the criteria may have reduced accuracy in certain populations, including patients with recurrent DVT, post-thrombotic syndrome, or those with extensive pre-existing venous disease.

Special Populations and Considerations

While Wells' Criteria has been validated across diverse populations, certain patient groups require special consideration. Pregnant women, who have elevated baseline DVT risk, may require modified interpretation of the criteria. Patients with recurrent DVT may have persistent symptoms from post-thrombotic syndrome, complicating the application of clinical criteria. Those with extensive malignancy or critical illness may have multiple overlapping risk factors, potentially inflating Wells' scores.

Elderly patients may present atypically, with DVT manifesting as unexplained functional decline or confusion rather than classic leg symptoms. In such cases, Wells' Criteria may be less applicable, and a lower threshold for diagnostic testing may be appropriate. Similarly, patients with significant cognitive impairment may be unable to provide accurate history, limiting the criteria's utility.

Evidence Base and Validation Studies

Wells' Criteria has undergone extensive validation since its original publication. Systematic reviews and meta-analyses have confirmed its utility across multiple clinical settings. The criteria demonstrate good inter-observer reliability when applied by trained clinicians, though some variability exists in the assessment of subjective criteria such as alternative diagnosis likelihood.

Validation studies have consistently demonstrated that Wells' Criteria, when combined with D-dimer testing, can safely reduce the need for imaging by 30-50% while maintaining high sensitivity for DVT detection. This reduction in imaging has important implications for healthcare resource utilization, patient convenience, and cost-effectiveness.

Recent studies have explored modifications to Wells' Criteria, including age-adjusted D-dimer thresholds and combination with other clinical prediction rules. However, the original Wells' Criteria remains the most widely validated and utilized tool for DVT probability assessment.

Limitations and Clinical Pearls

Several limitations of Wells' Criteria warrant recognition. The criteria were developed and validated primarily in emergency department and outpatient settings, and their performance in intensive care units or other specialized settings may differ. The criteria perform best for first-episode DVT and may be less accurate for recurrent events.

Some criteria, particularly the assessment of alternative diagnosis likelihood, require clinical experience and judgment, potentially introducing inter-observer variability. The criteria do not account for all DVT risk factors, such as inherited thrombophilias, which may be relevant in certain populations.

Clinical pearls for optimal use of Wells' Criteria include: (1) systematically assess all criteria rather than selectively applying some; (2) use quantitative measurements (calf circumference) when possible to enhance reliability; (3) consider the clinical context—criteria may perform differently in different settings; (4) integrate with D-dimer and imaging rather than using criteria in isolation; and (5) maintain clinical suspicion even with low scores if symptoms persist or worsen.

References

Wells PS, Anderson DR, Bormanis J, et al. Value of assessment of pretest probability of deep-vein thrombosis in clinical management. Lancet. 1997;350(9094):1795-1798.
Wells PS, Hirsh J, Anderson DR, et al. Accuracy of clinical assessment of deep-vein thrombosis. Lancet. 1995;345(8961):1326-1330.
Wells PS, Anderson DR, Rodger M, et al. Evaluation of D-dimer in the diagnosis of suspected deep-vein thrombosis. N Engl J Med. 2003;349(13):1227-1235.
Kearon C, de Wit K, Parpia S, et al. Diagnosis of DVT: Antithrombotic Therapy and Prevention of Thrombosis, 9th ed: American College of Chest Physicians Evidence-Based Clinical Practice Guidelines. Chest. 2012;141(2 Suppl):e351S-e418S.
Goodacre S, Sampson FC, Sutton AJ, et al. Variation in the diagnostic performance of D-dimer for suspected deep vein thrombosis. QJM. 2005;98(7):513-527.
Oudega R, Hoes AW, Moons KG. The Wells rule does not adequately rule out deep venous thrombosis in primary care patients. Ann Intern Med. 2005;143(2):100-107.
Constans J, Boutinet C, Salmi LR, et al. Comparison of four clinical prediction scores for the diagnosis of lower limb deep venous thrombosis in outpatients. Am J Med. 2003;115(6):436-440.
Wells PS, Owen C, Doucette S, Fergusson D, Tran H. Does this patient have deep vein thrombosis? JAMA. 2006;295(2):199-207.
Geersing GJ, Zuithoff NP, Kearon C, et al. Exclusion of deep vein thrombosis using the Wells rule in clinically important subgroups: individual patient data meta-analysis. BMJ. 2014;348:g1340.
Di Nisio M, van Es N, Büller HR. Deep vein thrombosis and pulmonary embolism. Lancet. 2016;388(10063):3060-3073.
Kearon C, Akl EA, Ornelas J, et al. Antithrombotic Therapy for VTE Disease: CHEST Guideline and Expert Panel Report. Chest. 2016;149(2):315-352.
Stein PD, Hull RD, Patel KC, et al. D-dimer for the exclusion of acute venous thrombosis and pulmonary embolism: a systematic review. Ann Intern Med. 2004;140(8):589-602.
Goodacre S, Stevenson M, Wailoo A, et al. How should we diagnose suspected deep-vein thrombosis? QJM. 2006;99(6):377-388.
Bates SM, Jaeschke R, Stevens SM, et al. Diagnosis of DVT: Antithrombotic Therapy and Prevention of Thrombosis, 9th ed: American College of Chest Physicians Evidence-Based Clinical Practice Guidelines. Chest. 2012;141(2 Suppl):e351S-e418S.
Wells PS, Anderson DR, Rodger M, et al. Excluding pulmonary embolism at the bedside without diagnostic imaging: management of patients with suspected pulmonary embolism presenting to the emergency department by using a simple clinical model and D-dimer. Ann Intern Med. 2001;135(2):98-107.