CTPA — Pulmonary Embolism
CTNICE NG1582020v2.0 · March 2026
Varies
EDInpatient
All imaging requests must be justified by an IR(ME)R practitioner (radiologist or radiographer)Required Assessment Tools
REQUIRED
Two-level Wells PE Score
Pre-test probability assessment — mandatory before CTPA unless haemodynamically unstable
>4 = PE likely
REQUIRED
D-dimer
Required if Wells ≤4
≥500 μg/L (or age-adjusted: age × 10 μg/L for >50 years)
OPTIONAL
PERC Rule
Optional — not validated for COVID-19 patients
CTPA indicated
— ANY of the following
- Wells >4 (PE likely)NICE NG158
- Wells ≤4 AND D-dimer ≥500 μg/LNICE NG158
- Age-adjusted D-dimer: age × 10 μg/L for patients >50 years
- Haemodynamically unstable with suspected massive PE — proceed directly (IMMEDIATE priority)
CTPA NOT indicated
— ALL of the following must be met
- Wells ≤4 AND D-dimer negative — PE excludedNICE NG158
- Wells ≤4 AND D-dimer below age-adjusted threshold
Chronic PE / CTEPH
— ANY of the following
- Not ED diagnosis — outpatient V/Q SPECT preferred
- Exception: haemodynamically unstable with acute-on-chronic PE
Notes
Warning
Wells score AND D-dimer must be documented — CTPA won't be authorised without pre-test probability
NICE NG158Information
Age-adjusted D-dimer: age × 10 μg/L for >50 years
Information
PERC rule not validated for COVID-19
Radiation Dose
CTPA effective dose ~2–6 mSv. Breast dose 10–44 mGy — consider for young female patients.
Pregnancy
Compression USS of legs first. V/Q SPECT preferred over CTPA (breast dose: CTPA 10–44 mGy vs V/Q 0.11–0.95 mGy). If breastfeeding: CTPA preferred.
Change Log
v1.02026-03-05Initial publication
v2.02026-03-08Age-adjusted D-dimer added. PERC rule noted. Pregnancy pathway detailed. V/Q comparison added.