Summary
Our goal was to evaluate the diagnostic utility of C-reactive protein (CRP) alone
or combined with clinical probability assessment in patients with suspected pulmonary
embolism (PE), and to compare its performance to a D-dimer assay. We conducted a prospective
study in which we performed a common immuno-turbidimetric CRP test and a rapid enzyme-linked
immunosorbent assay (ELISA) D-dimer test in 259 consecutive outpatients with suspected
PE at the emergency department of a teaching hospital. We assessed clinical probability
of PE by a validated prediction rule overridden by clinical judgment. Patients with
D-dimer levels ≥ 500 µg/l underwent a work-up consisting of lower-limb venous ultrasound,
spiral computer-ized tomography, ventilation-perfusion scan, or pulmonary angiography.
Patients were followed up for three months. Seventy-seven (30%) of the patients had
PE.The CRP alone had a sensitivity of 84% (95% confidence interval [CI).: 74 to 92%)
and a negative predictive value (NPV) of 87% (95% CI: 78 to 93%) at a cutpoint of
5 mg/l. Overall, 61 (24%) patients with a low clinical probability of PE had a CRP
< 5 mg/l. Due to the low prevalence of PE (9%) in this subgroup, the NPV increased
to 97% (95% CI: 89 to 100%). The D-dimer (cutpoint 500 µg/l) showed a sensitivity
of 100% (95% CI: 95 to 100%) and a NPV of 100% (95% CI: 94 to 100%) irrespective of
clinical probability and accurately rule out PE in 56 (22%) patients. Standard CRP
tests alone or combined with clinical probability assessment cannot safely exclude
PE.
Keywords
Pulmonary embolism - C-reactive protein - D-dimer - clinical probability assessment