Systematic review and meta-analysis of strategies for the diagnosis of suspected pulmonary embolism

Abstract

Objectives: To assess the likelihood ratios of diagnostic strategies for pulmonary embolism and to determine their clinical application according to pretest probability.

Data sources: Medline, Embase, and Pascal Biomed and manual search for articles published from January 1990 to September 2003.

Study selection: Studies that evaluated diagnostic tests for confirmation or exclusion of pulmonary embolism. DATA EXTRACTED: Positive likelihood ratios for strategies that confirmed a diagnosis of pulmonary embolism and negative likelihood ratios for diagnostic strategies that excluded a diagnosis of pulmonary embolism.

Data synthesis: 48 of 1012 articles were included. Positive likelihood ratios for diagnostic tests were: high probability ventilation perfusion lung scan 18.3 (95% confidence interval 10.3 to 32.5), spiral computed tomography 24.1 (12.4 to 46.7), and ultrasonography of leg veins 16.2 (5.6 to 46.7). In patients with a moderate or high pretest probability, these findings are associated with a greater than 85% post-test probability of pulmonary embolism. Negative likelihood ratios were: normal or near normal appearance on lung scan 0.05 (0.03 to 0.10), a negative result on spiral computed tomography along with a negative result on ultrasonography 0.04 (0.03 to 0.06), and a d-dimer concentration < 500 mug/l measured by quantitative enzyme linked immunosorbent assay 0.08 (0.04 to 0.18). In patients with a low or moderate pretest probability, these findings were associated with a post-test probability of pulmonary embolism below 5%. Spiral computed tomography alone, a low probability ventilation perfusion lung scan, magnetic resonance angiography, a quantitative latex d-dimer test, and haemagglutination d-dimers had higher negative likelihood ratios and can therefore only exclude pulmonary embolism in patients with a low pretest probability.

Conclusions: The accuracy of tests for suspected pulmonary embolism varies greatly, but it is possible to estimate the range of pretest probabilities over which each test or strategy can confirm or rule out pulmonary embolism.

Fig 1

Positive likelihood ratios (squares) and 95% confidence intervals for strategies used to confirm a diagnosis of pulmonary embolism. Size of square is related to variance of study. Broken line represents pooled positive likelihood ratio, and limits of diamond represents 95% confidence intervals of pooled ratios

Fig 2

Negative likelihood ratios (squares) and 95% confidence intervals for strategies used to exclude a diagnosis of pulmonary embolism. Size of square related to variance of study. Broken line represents pooled negative likelihood ratio, and limits of diamond represents 95% confidence intervals of pooled ratios

Fig 3

Negative likelihood ratios (squares) and 95% confidence intervals for strategies used to exclude a diagnosis of pulmonary embolism on basis of d-dimer tests. Size of square is related to variance of study. Broken line represents pooled negative likelihood ratio, and limits of diamond represent 95% confidence interval of pooled negative likelihood ratio

Fig 4

Post-test probability according to pre-test probability and pooled values (solid line) or limits of 95% confidence intervals (broken lines) of the positive likelihood ratio

Fig 5

Post-test probability according to pre-test probability and pooled values (solid line) or limit of 95% confidence intervals (broken lines) of the negative likelihood ratio

Fig 6

Diagnostic tests for pulmonary embolism that allow accurate exclusion (post-test probability <5%) and accurate confirmation of the condition (post-test probability >85%) for three levels of clinical probability. Pulmonary angiography is reference method and is supposed to rule in or rule out pulmonary embolism for all values of clinical probability