Usefulness of D-dimer, blood gas, and respiratory rate measurements for excluding pulmonary embolism

Abstract

Background-A study was undertaken to assess the usefulness of the SimpliRED D-dimer test, arterial oxygen tension, and respiratory rate measurement for excluding pulmonary embolism (PE) and venous thromboembolism (VTE). Methods-Lung scans were performed in 517 consecutive medical inpatients with suspected acute PE over a one year period. Predetermined end points for objectively diagnosed PE in order of precedence were (1) a post mortem diagnosis, (2) a positive pulmonary angiogram, (3) a high probability ventilation perfusion lung scan when the pretest probability was also high, and (4) the unanimous opinion of an adjudication committee. Deep vein thrombosis (DVT) was diagnosed by standard ultrasound and venography. Results-A total of 40 cases of PE and 37 cases of DVT were objectively diagnosed. The predictive value of a negative SimpliRED test for excluding objectively diagnosed PE was 0.99 (error rate 2/249), that of PaO 2 of >80 mm Hg (10.7 kPa) was 0.97 (error rate 5/160), and that of a respiratory rate of <20/min was 0.95 (error rate 14/308). The best combination of findings for excluding PE was a negative SimpliRED test and PaO 2 >80 mm Hg, which gave a predictive value of 1.0 (error rate 0/93). The predictive value of a negative SimpliRED test for excluding VTE was 0.98 (error rate 5/249). Conclusions-All three of these observations are helpful in excluding PE. When any two parameters were normal, PE was very unlikely. In patients with a negative SimpliRED test and PaO 2 of >80 mm Hg a lung scan is usually unnecessary. Application of this approach for triage in the preliminary assessment of suspected PE could lead to a reduced rate of false positive diagnoses and considerable resource savings. (Thorax 1998;53:830-834) Keywords: pulmonary embolism; deep vein thrombosis; D-dimer; blood gas; respiratory rate Pulmonary embolism (PE) and deep vein thrombosis (DVT) are disorders of importance in most areas of medicine. The clinical presentation of PE is notoriously non-specific and may mimic many other acute cardiorespiratory illnesses. In cases of suspected PE the ventilation perfusion (VQ) lung scan is a commonly requested examination. A normal VQ scan eVectively excludes PE, and a high probability VQ scan in an appropriate clinical setting oVers good but not incontrovertible evidence that PE has occurred.1 However, in practice up to 70% of lung scans show non-specific abnormalities, and additional tests, including pulmonary angiography, are often required.2 Furthermore, the VQ scan is a relatively expensive and technology dependent screening procedure, and more selective utilisation of this test has been advocated. 3 For example, the recently published British Thoracic Society guidelines suggested that a normal D-dimer level (measured by ELISA) excludes PE, as does a respiratory rate of <20/min and the absence of pleuritic pain and hypoxaemia. 4 These suggestions, while plausible, remain relatively untested.D-dimer is a product of fibrinolysis. Levels of D-dimer are raised in many conditions incl...

The nurse endoscopy scene

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