ABSTRACT
Pulmonary embolism is a common clinical disorder that is associated with high morbidity and mortality if untreated. The diagnosis of pulmonary embolism is difficult because the clinical presentation is non-specific all of the objective tests have limitations. The aim of this study was to evaluate the utility of the arterial partial pressure of oxygen, alveolo-arterial oxygen gradient and right to left shunt fraction as screening tests in the diagnosis of acute pulmonary embolism and to set an equation including the three variables with a more better clinical probability. Eighty patients presented with clinical suspicion of pulmonary embolism were studied including 57 patients as a test group with objectively confirmed diagnosis and a control group of 23 patients with the diagnosis of pulmonary embolism excluded on confirmatory workup. Arterial oxygen tension and alveolo-arterial oxygen gradient proved to have significant sensitivity and positive predictive value. The right to left shunt fraction has excellent sensitivity, positive predictive value and diagnostic likelihood ratio. However, the probability equation of A-alpha X SH/PaO2 has the best of over all diagnostic values. In conclusion, the probability equation suggested in the present study is a simple and accurate clinical screening test in cases with suspected PE. Compared to the other study parameters it has excellent diagnostic values including sensitivity, specificity, positive predictive value, negative predictive value and diagnostic likelihood ratio. The value of PEQ defines the degree of severity of PE