Accuracy of X-ray with perfusion scan in young patients with suspected pulmonary embolism.

BACKGROUND: Computed tomography pulmonary angiogram (CTPA) has become the standard test in the diagnostic workup of patients with suspected pulmonary embolism (PE). However, young patients may have an increased risk of cancer with CTPA. Perfusion scanning combined with chest X-ray (X/Q) may offer an adequate alternative, but has never been prospectively validated. We directly compared this strategy with CTPA in patients aged ≤50years with suspected PE. METHODS: Consecutive patients with a likely clinical probability or an abnormal D-dimer level underwent both CTPA and X/Q. Two trained and experienced nuclear physicians independently analyzed the X/Q-scans. The accuracy of X/Q according to the PISAPED criteria was calculated in terms of sensitivity, specificity, positive predictive value (PPV), and negative predictive value (NPV). RESULTS: Seventy-six patients were included, with a PE rate of 33%. The inter-observer agreement for X/Q-scan reading was high (κ=0.89). After consensus reading, 21 patients (28%) were categorized as 'PE present', 53 (70%) as 'PE absent', and two (2.6%) as 'non-diagnostic'. In 22%, there was a discrepancy between the X/Q-scan and CPTA for the diagnosis or exclusion of PE. The PPV and NPV were 71% and 83%, respectively. CONCLUSION: In patients with a high risk of PE, a diagnostic strategy of chest X-ray and perfusion scanning using the PISAPED criteria seems less safe than CTPA. Additional studies should further investigate this diagnostic algorithm.

Variable D-dimer thresholds for diagnosis of clinically suspected acute pulmonary embolism.

BACKGROUND: Computed tomography pulmonary angiography (CTPA) is frequently requested using diagnostic algorithms for suspected pulmonary embolism (PE). For suspected deep vein thrombosis, it was recently shown that doubling the D-dimer threshold in patients with low pretest probability safely decreased the number of ultrasonograms. We evaluated the safety and efficiency of a similar strategy in patients with suspected PE. METHODS: We performed a post-hoc analysis of 2213 consecutive patients of two cohort studies with suspected PE who were managed according to current standards: PE ruled out in case of unlikely probability (Wells rule ≤ 4 points) and a D-dimer level < 0.5 µg mL(-1) . CTPA was performed in all other cases. All patients were followed for 3 months. We calculated 3-month venous thromboembolism (VTE) incidence and the number of required CTPAs for selective D-dimer thresholds in patients with low clinical probability (< 2 points, D-dimer threshold < 1.0 µg mL(-1) ) and intermediate probability (2-6 points, D-dimer threshold < 0.5 µg mL(-1) ). RESULTS: Using standard management, PE could be excluded without CTPA in 26% of patients, with a 3-month VTE incidence of 0.88% (95% confidence interval [CI] 0.29-2.1%). Using selective D-dimer thresholds, PE could be excluded without CTPA in 36% of patients, with a 3-month VTE incidence of 2.1% (95% CI 1.2-3.4%) in patients managed without CTPA, an increase of 1.2 percentage points (95% CI -0.3 to 2.2). CONCLUSIONS: Applying selective D-dimer thresholds reduces the need for CTPA by 11 percentage points but is associated with an increased failure rate. Prospective studies should evaluate the safety and net clinical benefit of this approach.