Should a patient with unilateral ankle swelling and elevated D-dimer levels be sent to the emergency room for potential deep vein thrombosis (DVT) or pulmonary embolism (PE) evaluation?

Should This Patient Be Sent to the Emergency Room?

Yes, a patient with unilateral ankle swelling and elevated D-dimer should be sent to the emergency room immediately for urgent imaging to rule out deep vein thrombosis (DVT), as this combination represents an intermediate-to-high clinical probability scenario that requires same-day diagnostic evaluation and cannot be safely managed in an outpatient setting without imaging. 1, 2

Clinical Risk Stratification

The combination of unilateral leg swelling with elevated D-dimer places this patient in a higher-risk category that mandates urgent evaluation:

• Unilateral leg swelling alone increases the pretest probability of DVT to 42.5% according to validated clinical decision rules, making this an "unsafe" patient for D-dimer-based exclusion strategies 1
• When combined with a positive D-dimer, the probability of DVT becomes sufficiently high (>25-40%) that imaging cannot be deferred 1, 2
• The revised Geneva score assigns 4 points specifically for "pain on lower-limb deep venous palpation and unilateral oedema," which alone places patients in the intermediate probability category 1

Why Emergency Department Evaluation Is Necessary

Imaging must be obtained urgently because:

• A positive D-dimer in the setting of unilateral leg swelling requires confirmatory imaging with compression ultrasonography of the proximal veins or whole-leg ultrasound before DVT can be excluded 1, 2
• The American College of Chest Physicians explicitly recommends that patients with moderate-to-high pretest probability should undergo proximal compression ultrasound or whole-leg ultrasound rather than relying on D-dimer alone 1
• A positive D-dimer alone cannot diagnose DVT and must always be followed by imaging, but it also cannot safely exclude DVT in patients with clinical findings like unilateral swelling 2, 3

Critical Time-Sensitive Considerations

The emergency department setting is appropriate because:

• If DVT is confirmed, anticoagulation should be initiated promptly to prevent pulmonary embolism, which occurs in approximately 50% of patients with untreated proximal DVT 4
• The 3-month risk of venous thromboembolism complications increases significantly with delayed diagnosis and treatment 4, 5
• Emergency departments have immediate access to compression ultrasonography, which is the first-line imaging modality for suspected DVT 1

Specific Diagnostic Pathway in the Emergency Department

Once in the ER, the following evaluation should occur:

1. Immediate compression ultrasonography of the proximal veins (or whole-leg ultrasound if available) should be performed 1
2. If proximal ultrasound is negative but clinical suspicion remains high due to the unilateral swelling, repeat proximal ultrasound in 1 week or proceed to whole-leg ultrasound 1
3. If ultrasound is positive for DVT, initiate anticoagulation immediately without need for confirmatory venography 1

Important Pitfalls to Avoid

Do not attempt outpatient management in this scenario:

• Never use a positive D-dimer alone to diagnose DVT—imaging confirmation is mandatory 2, 3
• Never discharge a patient with unilateral leg swelling and positive D-dimer without imaging, as this represents a 42.5% probability of DVT 1
• Do not schedule outpatient ultrasound for "next available appointment"—this requires same-day evaluation 1, 4
• Avoid the misconception that D-dimer "rules out" DVT in symptomatic patients; its value is in ruling out DVT when negative in LOW probability patients only 1, 2

Additional Risk Factors That Strengthen ER Referral

If any of the following are present, the urgency increases further:

• Age >50 years, heart rate >95 bpm, recent surgery/immobilization, active cancer, or previous VTE history all increase the clinical probability score and make DVT more likely 1
• Extremely elevated D-dimer (>5000 μg/L) is associated with serious illness including VTE, sepsis, or malignancy in 89% of cases and warrants immediate comprehensive evaluation 6
• If D-dimer is 3-4 times above normal (>1.5-2.0 mg/L), this signifies substantial thrombin generation and increased mortality risk, warranting hospital admission consideration even without severe symptoms 2, 3