ClinicalV/Q scans vs CTPA
One study with 1417 patients showed that there was a decrease in mortality in patients who had received CTPA scans compared to V/Q scans amongst patients who had initially been excluded; this may be of clinical importance, but there is a lot of uncertainty (MODERATE QUALITY).
One study with 1417 patients showed that it is very uncertain whether there is a clinically important difference in symptomatic PE or proximal DVT events in VTE patients whom had initially been excluded (LOW QUALITY).
V/Q scans (planar lung scintigraphy)
Five studies involving 1142 patients showed that sensitivity and specificity for planar lung scintigraphy ranged from 41 to 100% and 72 to 97% respectively. This means that 0 to 59 out of 100 patients with PE will be missed with planar lung scintigraphy. The specificity suggests that 3 to 28 out of 100 people without PE will be identified as having the condition. The included studies report a range of values for the specificity and sensitivity of ventilation perfusion scans; this means that there is variation in how good these scans are at diagnosing PE in patients. The included studies also vary with respect to whether indeterminate cases were included; where indeterminate cases are excluded the sensitivity and specificity of the diagnostic test could be overestimated, making it appear more effective (VERY LOW QUALITY).
One small study with 41 patients showed sensitivity and specificity of V/Q (SPECT) to be calculated as 100% and 87% respectively. For the purposes of ruling out PE this suggests that no patients with PE will be missed when using V/Q (SPECT). The specificity suggests that 13 out of 100 people without PE will be identified as having the condition. However there is a lot of uncertainty surrounding this outcome as the figures calculated for sensitivity and specificity are likely to be overestimated as they did not take account of indeterminate cases (VERY LOW QUALITY).
EconomicThe most cost-effective strategy involves managing patients according to their two-level PE Wells score: if PE is likely offer a CTPA; if PE is unlikely offer a D-dimer and a CTPA only if the D-dimer is positive. There is a high uncertainty as to whether adding a proximal ultrasound of the lower limbs in patients with a likely PE when the CTPA is negative is cost-effective. Strategies involving ventilation perfusion scan were not cost-effective in the base case. This evidence is directly applicable but it has potentially serious limitations.

From: 6, Diagnosis of pulmonary embolism

Cover of Venous Thromboembolic Diseases
Venous Thromboembolic Diseases: The Management of Venous Thromboembolic Diseases and the Role of Thrombophilia Testing [Internet].
NICE Clinical Guidelines, No. 144.
National Clinical Guideline Centre (UK).
Copyright © 2012, National Clinical Guideline Centre.

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