What are the guidelines for a percutaneous (perc) test in a medical context?

Pulmonary Embolism Rule-out Criteria (PERC) Guidelines

The PERC rule is a validated clinical decision tool that safely rules out pulmonary embolism in low-risk patients without requiring further testing when all eight criteria are met, avoiding unnecessary imaging and potential harm. 1

PERC Criteria Components

• The PERC rule consists of 8 objective criteria that must all be negative to safely rule out PE 1:
  1. Age < 50 years
  2. Heart rate < 100 beats per minute
  3. Oxygen saturation ≥ 95% on room air
  4. No unilateral leg swelling
  5. No hemoptysis
  6. No recent trauma or surgery (requiring hospitalization in previous 4 weeks)
  7. No prior history of venous thromboembolism (VTE)
  8. No hormone use (exogenous estrogen)

Proper Application of PERC

• PERC should only be applied to patients already determined to have low pretest probability of PE (using clinical gestalt or validated tools like Wells criteria) 2, 1
• PERC should not be used as a general screening tool for all patients with respiratory symptoms 1, 3
• When all criteria are met (PERC negative) in a low-risk patient, the post-test probability of VTE is <2%, making it safe to exclude PE without further testing 2, 4
• Applying PERC to intermediate or high-risk patients may lead to missed diagnoses 1, 5

Clinical Performance and Safety

• Meta-analysis data shows PERC has a sensitivity of 97% and specificity of 22%, with a very low miss rate of only 0.3% when properly applied 1, 5
• In a large multicenter validation study with 8,138 patients, PERC demonstrated a sensitivity of 97.4% and a false-negative rate of only 1.0% 4
• Using PERC could safely avoid approximately 20-25% of diagnostic tests in appropriate patients 6, 4
• Community hospital studies have shown PERC could reduce CT scans by 23% with a negative predictive value of 100% 6

Diagnostic Algorithm for Suspected PE

1. Assess pretest probability using clinical gestalt or validated tools (Wells criteria) 2, 3
2. For low pretest probability patients, apply PERC 2, 1
3. If PERC negative (all criteria met): safely rule out PE without further testing 2, 1
4. If PERC positive (any criteria not met): proceed with D-dimer testing 2, 3
5. For D-dimer testing, use age-adjusted thresholds (age × 10 ng/mL) for patients over 50 years 2
6. If D-dimer negative: rule out PE 2, 3
7. If D-dimer positive: proceed to imaging (CT pulmonary angiography) 2, 3

Common Pitfalls and Caveats

• Applying PERC to patients with intermediate or high pretest probability is dangerous and can lead to missed diagnoses 1, 5
• Using PERC as a standalone tool without first determining pretest probability is inappropriate 2, 1
• D-dimer testing in PERC-negative patients leads to unnecessary imaging in about 15% of cases due to false positives 7
• The prevalence of PE in different populations affects PERC performance - European studies have shown higher PE prevalence, potentially affecting rule safety 8, 7
• In patients with comorbid conditions likely to cause elevated D-dimer, D-dimer testing has limited utility and should be bypassed in favor of direct imaging 3