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

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 terror rate 2/249), that of Pao(2) of greater than or equal to 80 mm Hg (10.7 kPa) was 0.97 terror rate 5/160), and that of a respiratory rate of less than or equal to 20/min was 0.95 terror rate 14/308). The best combination of findings for excluding PE was a negative SimpliRED test and Pao(2) greater than or equal to 80 mm Hg, which gave a predictive value of 1.0 terror rate 0/93). The predictive value of a negative SimpliRED test for excluding VTE was 0.98 terror 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 greater than or equal to 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.