Diagnosis

Diagnosing PE includes an evaluation for DVT. Physical examination for signs of DVT (asymmetry in calf or thigh diameter, calf tenderness, Homans sign) are relatively insensitive and nonspecific, and other tests (venous Doppler ultra-sonography or spiral CT with contrast) can more accurately confirm the presence of significant underlying DVT.

Once suspected, PE must be confirmed or ruled out with a high degree of certainty. Failure to treat could be life threatening, but treatment carries significant risks as well. Clinical decision rules using objective scoring algorithms help establish pretest probability (high, intermediate, or low), which in turn enhances predictive value of other tests for PE (Ebell, 2004). One common decision tool uses only history and physical examination variables (Wells et al., 2001), and another scoring system adds variables from chest x-ray and arterial blood gas measurements (Wicki et al., 2001).

Several qualitative, semiquantitative, and quantitative laboratory methods are available for measuring D-dimer. Any negative D-dimer test can help exclude the diagnosis of PE in patients with low pretest probability of disease, but for patients with moderate pretest probability, only quantitative D-dimer test by enzyme-linked immunosorbent assay (ELISA) less than 500 \ig/L can effectively rule out PE. Spiral CT with contrast and magnetic resonance angiography (MRA), two alternative imaging studies widely replacing V/Q scan, are more accessible and accurate in patients with underlying heart or lung disease, and perhaps more accurate for centrally located than peripheral emboli. Spiral CT also offers the advantage of potentially diagnosing other conditions, and when ordered in a PE protocol, may be combined with CT of the lower extremities to evaluate possible DVTs. Table 18-5 summarizes the results of strategies for excluding the diagnosis of PE (using criteria of post-test probability <5%) or for confirming the diagnosis (post-test probability >85%) (Roy et al., 2005).

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