What percentage of patients with a negative Deep Vein Thrombosis (DVT) result will also have a negative Pulmonary Embolism (PE) result?

Negative DVT and Pulmonary Embolism Correlation

A negative DVT result has approximately 99% negative predictive value for pulmonary embolism, meaning that about 99% of patients with a negative DVT test will also have a negative PE result. 1

Relationship Between DVT and PE

The relationship between DVT and PE is well-established in the medical literature:

• PE originates from DVT in the lower limbs in approximately 90% of cases 1
• In patients with proven PE, DVT can be found in about 70% of cases using venography 1
• Using compression ultrasonography (CUS), DVT is detected in 30-50% of patients with PE 1

Diagnostic Implications

When evaluating patients with suspected venous thromboembolism (VTE), the following considerations are important:

Negative DVT Testing and PE Risk

• In a prospective management study, only 3 out of 324 patients (0.9%, 95% CI 0.3-2.7%) had a proximal DVT despite a negative multidetector CT (MDCT) 1
• In the Christopher Study, the 3-month thromboembolic risk in patients left untreated because of a negative CT was only 1.1% (95% CI 0.6-1.9%) 1
• In a Canadian trial comparing V/Q scan and CT, only 7 of 531 patients with a negative CT had a DVT and only one had a thromboembolic event during follow-up 1

Reliability of Negative DVT Results

• A normal perfusion lung scan reliably excludes PE, with only 0.8% of patients with normal scan results having proximal DVT on ultrasonography 1
• Of these patients with normal scans and no anticoagulation, none had thromboembolic events during follow-up 1

Important Clinical Considerations

Limitations of DVT Testing

• A single normal leg ultrasound should not be relied upon for exclusion of subclinical DVT 1
• The sensitivity of CUS for detecting PE on MDCT is only about 39%, though specificity is high at 99% 1
• In trauma patients, a negative D-dimer test does not reliably exclude DVT or PE within the first 4 days after injury (false negative rate of 24%) 2

Clinical Impact of DVT with PE

• PE with concomitant DVT carries a higher 3-month mortality (12.9%) compared to PE without DVT (4.6%) 3
• When compared to controls without VTE, only PE with DVT showed significantly increased mortality risk (adjusted hazard ratio: 2.6,95% CI 1.4-4.7) 3

Diagnostic Algorithm

1. For low clinical probability patients:

   • Apply PERC rule if appropriate (age <50, HR <100, O2 sat ≥95%, no VTE history, etc.) 4
   • If PERC negative: No further testing needed
   • If PERC positive: Order D-dimer test 4

2. For intermediate clinical probability patients:

   • Order D-dimer test
   • If D-dimer negative: PE can be excluded
   • If D-dimer positive: Proceed to imaging (CTPA) 4

3. For high clinical probability patients:

   • Proceed directly to imaging (CTPA) without D-dimer testing 4

Pitfalls to Avoid

• Do not rely solely on a single negative leg ultrasound to exclude subclinical DVT 1
• Do not assume a negative D-dimer excludes VTE in all clinical scenarios, particularly in trauma patients within 4 days of injury 2
• Do not overlook the clinical significance of an associated DVT when diagnosing PE, as it impacts mortality risk 3
• Do not skip clinical probability assessment, as this can lead to incorrect diagnosis 4

The high negative predictive value of a negative DVT test for PE (approximately 99%) makes it a valuable tool in the diagnostic algorithm, but it should be used in conjunction with clinical probability assessment and appropriate follow-up testing when indicated.