Arterial blood gases (ABGs) will commonly reveal hypoxemia with reduced partial pressure of oxygen, which may suggest PE, but is not diagnostic as ABGs can be normal in up to 18% of patients The negative predictive value of a normal partial pressure of oxygen may not justify performing this painful and occasionally difficult procedure in the diagnostic evaluation for PE in children BNP and troponin have also been shown to be of little diagnostic utility The laboratory study which has traditionally played the most significant role in the evaluation of adult patients with suspected PE has been the D-dimer Measurement of fibrin degradation products produced when plasmin splits crosslinked fibrin is a sensitive marker for intravascular clot Such biomarkers will be positive as early as hour after thrombus formation, with a circulating half-life of to hours However, because of continued PE fibrinolysis, plasma D-dimer levels are commonly elevated for at least week Sensitive D-dimer testing uses quantitative or semiquantitative new generation immunoturbidimetric, latexagglutination-based, or rapid enzyme-linked immunosorbent assays (ELISA) These newer generation assays are preferred because they have reported sensitivities of 96% to 98% for the diagnosis of PE, and are reported more quickly than previous generation testing Nonetheless, because of the presence of wide variability in performance of each assay, it is important for practitioners to be aware of the characteristics within their laboratory when incorporating results into their medical decision making In low- and intermediate-risk patients, a Ddimer ≤500 ng/mL effectively excludes PE and usually no further testing is required The applicability of D-dimer testing to evaluation and management of pediatric patients with suspected PE is discussed below in conjunction with imaging decision making Radiologic studies are important aspects in the evaluation of patients with possible PE CXRs are recommended because they are noninvasive, though they are rarely diagnostic and can be normal in up to 22% of patients diagnosed with PE The presence of a segmental pulmonary infiltrate with an ipsilateral elevated hemidiaphragm is suggestive of a PE; however, even these radiographic findings are not pathognomonic Hampton hump and Westermark sign are rarely seen, but should also raise the possibility of PE if present Occasionally, however, chest films will uncover an alternative diagnosis for a patient’s symptoms, obviating the need for further evaluation of patients at low risk for PE For years, V/Q scans were the mainstay of imaging in patients with concern for PE A characteristic pattern of normal ventilation in a poorly perfused area of lung is considered high probability and effectively establishes the diagnosis of PE Similarly, a normal V/Q scan essentially excludes the diagnosis