Questions: Venous Thromboembolism: DVT and Pulmonary Embolism

Question 1

A 65-year-old patient is 5 days post-abdominal surgery with a D-dimer of 2.8 µg/mL (elevated). The most appropriate clinical interpretation is:

• A. This confirms DVT or PE; anticoagulation should begin immediately.
• B. This strongly suggests active thrombosis, warranting urgent imaging and likely treatment.
• C. Elevated D-dimer in this postoperative context is non-specific; imaging is required to diagnose or exclude VTE.
• D. This is a normal postoperative finding and requires no further evaluation.

Answer: (C)

D-dimer has poor specificity — surgery, infection, trauma, and malignancy all elevate it without VTE. In a postoperative patient, an elevated D-dimer is expected and provides almost no diagnostic information. The asymmetry is critical: D-dimer is useful for *ruling out* VTE in low-probability outpatient patients (high sensitivity), but a positive result in hospitalized patients is nearly meaningless. Imaging is required to diagnose VTE regardless of D-dimer level in this context.

Question 2

A patient presents with acute pleuritic chest pain and hemoptysis. Compression ultrasound of both legs is negative. The correct interpretation is:

• A. PE is excluded, because PE arises from DVT and the negative leg ultrasound would have detected it.
• B. The absence of leg symptoms makes PE very unlikely, and further workup can be deferred.
• C. PE remains possible; a significant proportion of PEs occur without a detectable DVT on ultrasound.
• D. A negative leg ultrasound is sufficient to exclude PE without CT pulmonary angiography.

Answer: (C)

The common misconception is that PE always follows from detectable DVT. In practice, a substantial minority of PE cases occur without detectable DVT — the thrombus may have fully embolized, originated in pelvic veins not imaged by leg ultrasound, or been too small to detect. A negative compression ultrasound does not exclude PE, and clinical suspicion with appropriate Wells scoring should guide whether CT pulmonary angiography is needed.

Question 3

In massive pulmonary embolism, right ventricular failure occurs because the normal RV is a thin-walled, low-pressure chamber not equipped to compensate for sudden, severe increases in afterload.

• T. True
• F. False

Answer: True

The normal RV is adapted to the low-resistance pulmonary circulation. When large central emboli obstruct main pulmonary arteries, afterload doubles or triples acutely. The thin-walled RV cannot generate the pressure needed to push blood through, dilates, and fails. The dilating RV shifts the interventricular septum leftward (D-sign on echocardiography), compromises LV filling, and produces obstructive shock. This cascade explains the high mortality (>30% at 30 days) of massive PE.

Question 4

D-dimer testing is equally useful for diagnosing (ruling in) and excluding (ruling out) venous thromboembolism in clinical practice.

• T. True
• F. False

Answer: False

D-dimer has very high sensitivity (>97%) but very poor specificity for VTE. This asymmetry makes it a reliable rule-out test — a negative result in a low-probability patient safely excludes VTE without imaging. But a positive result is nearly uninformative, because many common conditions (surgery, infection, malignancy, trauma, pregnancy) elevate D-dimer without VTE. The rule is: D-dimer is for ruling out, not ruling in.

Question 5

Explain the clinical asymmetry between a negative D-dimer result and a positive D-dimer result when evaluating for VTE.

Model answer: D-dimer has very high sensitivity (>97%) for active thrombosis — it is almost always elevated when VTE is present. Therefore, a negative result reliably excludes VTE in low-pretest-probability patients: if VTE were present, D-dimer would almost certainly be elevated. A positive result, however, has very poor specificity — infection, surgery, malignancy, trauma, and pregnancy all elevate D-dimer without any thrombosis. Positive D-dimer tells you little in most clinical settings. The asymmetry: negative = useful (rules out); positive = often uninformative (does not rule in).

This asymmetry is a direct consequence of the sensitivity/specificity tradeoff. D-dimer is most useful precisely in the population where you might think it matters least: the low-probability outpatient where imaging would otherwise be needed.