Likelihood ratios increase diagnostic certainty in pulmonary embolism

Chu, Kevin and Brown, Anthony F. T. (2005) Likelihood ratios increase diagnostic certainty in pulmonary embolism. Emergency Medicine Australasia, 17 4: 322-329. doi:10.1111/j.1742-6723.2005.00754.x

Author Chu, Kevin
Brown, Anthony F. T.
Title Likelihood ratios increase diagnostic certainty in pulmonary embolism
Journal name Emergency Medicine Australasia   Check publisher's open access policy
ISSN 1742-6731
Publication date 2005-08-01
Sub-type Article (original research)
DOI 10.1111/j.1742-6723.2005.00754.x
Open Access Status Not Open Access
Volume 17
Issue 4
Start page 322
End page 329
Total pages 8
Place of publication Carlton, Vic, Australia
Publisher Wiley-Blackwell
Language eng
Subject 110305 Emergency Medicine
Abstract Pulmonary embolism (PE) is a difficult diagnosis to confirm. The choice of tests has led to a myriad of algorithms. Diagnostic uncertainty can be quantified by the application of the tests’ likelihood ratios (LR). Positive and negative LR enable the conversion of a pretest to a post-test probability, given a positive and negative test result, respectively. Thus, a pretest probability of <17% and a negative D-dimer with a negative LR of 0.05 (sensitivity 98%, specificity 40%) lead to a post-test probability of PE of <1%. Ventilation perfusion (V/Q) scans with a normal, very low, low, intermediate and high probability result have an LR of 0, 0.125, 0.25, 1 and 17, respectively. Also, patients with a V/Q scan result other than normal or high probability still have a post-test probability of PE from 3 to 65%. Positive and negative computed tomography pulmonary angiograms (CTPA) have an LR of 8.6 and 0.06, respectively (sensitivity 95%, specificity 89%). Patients with a high pretest probability and negative CTPA again still have a post-test probability of more than 10%. However, as the post-test probability after one test becomes the pretest probability for the next, test results used cumulatively progressively narrow the gap to a final diagnosis. The post-test probability after a D-dimer, V/Q scan, CTPA, leg ultrasound or pulmonary angiography, alone or in any combination or in any order, can be calculated using their LR. Use of LR thus assists in the precise interpretation of test results, such as in complex algorithms for PE.
Keyword D-dimer
Diagnostic test
Likelihood ratio
Pulmonary embolism
Q-Index Code C1
Institutional Status Non-UQ

Document type: Journal Article
Sub-type: Article (original research)
Collections: Excellence in Research Australia (ERA) - Collection
School of Medicine Publications
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Created: Wed, 01 Apr 2009, 00:45:52 EST by Juliette Grosvenor on behalf of Faculty Of Health Sciences