A stepwise PE evaluation tool. Calculate Wells PE score, apply PERC rule if appropriate,
then compute the Kohn 2017 interval likelihood ratio from a quantitative D-dimer to derive
a Bayesian post-test probability.
1
Wells Score
2
PERC Rule
3
D-Dimer iLR
Wells PE Criteria Wells 2001
0
Low probability
Estimated PE prevalence: ~2% (Wells <2) Pre-test probability for D-dimer calculation: ~2%
Interpretation
Score < 2: Low (PE prevalence ~2%) · Score 2–6: Moderate (~17%) · Score > 6: High (~40%)
Dichotomized: ≤ 4 = PE Unlikely (~12%) · > 4 = PE Likely (~37%) Note: "PE diagnosis more likely than alternative" criterion requires clinical judgment.
PERC Rule Kline 2004
PERC Result
Pre-test Probability
Auto-populated from Wells score. Adjust if needed.
15%Low (Wells ≤4)
1%LowModerateHigh85%
D-Dimer Result Kohn AEM 2017
ng/mL
Standard cutoff: 500 ng/mL ·
Age-adjusted (>50): age × 10 ng/mL ·
PEGeD low-PTP cutoff: 1,000 ng/mL
Bayesian Result
Pre-test
—
Post-test
—
Kohn 2017 — Full iLR Reference Table
Interval (ng/mL)
Observed iLR
95% CI
Fitted iLR
Post-test @ PTP
Anchor: 1,000–1,499 ng/mL iLR = 0.98 ≈ 1.0. Between-interval factor = 2.0 (95% CI 1.9–2.1).
n = 6,013 from 5 pooled PE management studies. Bayesian calc uses observed iLR.
Fagan Nomogram
Pre-test:—
iLR (Kohn 2017 observed):—
Post-test:—
Log-odds scale. Line pivots through iLR from pre-test (left) to post-test (right).
Evidence Base
Wells PS et al. "Excluding pulmonary embolism at the bedside without diagnostic imaging." Ann Intern Med. 2001;135:98–107 — derivation of the Wells PE clinical prediction rule. Kline JA et al. "Clinical criteria to prevent unnecessary diagnostic testing in emergency department patients with suspected pulmonary embolism." J Thromb Haemost. 2004;2:1247–1255 — PERC rule derivation. Kohn MA, Klok FA, van Es N. "D-dimer Interval Likelihood Ratios for Pulmonary Embolism." Acad Emerg Med. 2017;24:832–837 — pooled iLR model (n=6,013). Kearon C et al. PEGeD study. NEJM. 2019;381:2125–2134 — PTP-stratified D-dimer cutoffs validated prospectively.
⚠ Decision support only. This tool does not replace clinical judgment or institutional protocols.
Wells score interpretation requires physician assessment; "PE diagnosis more likely than alternative" is a subjective criterion.
PERC rule is validated only in low pre-test probability patients. D-dimer iLRs (Kohn 2017) were derived from high-sensitivity
quantitative ELISA-based assays and may vary by platform. Always confirm with attending physician and local guidelines.