A decision analysis to determine a testing threshold for computed tomographic angiography and d-dimer in the evaluation of aortic dissection

Objective

The objective of this study is to determine at what probability of thoracic aortic dissection (TAD) to use a computed tomographic angiography (CTA) or a d-dimer test.

Methods

We used decision analysis software to determine the testing threshold (TT) for 3 hypothetical decisions when evaluating for TAD: (1) no testing vs CTA, (2) no testing vs d-dimer, and (3) CTA vs d-dimer. One- and 2-way sensitivity analyses were performed to determine which variables were drivers of the TTs.

Results

We found TTs of 0.03%, 0.013%, and 0.6% for decisions 1, 2, and 3, respectively. For all 3 decisions, patient age and the annual rate of cancer were major drivers of the TT. In decisions 1 and 2, the probability of acute renal failure requiring renal replacement therapy was a major driver, whereas d-dimer sensitivity was a major driver for decision 3.

Conclusion

The TTs for TAD are low and reflect the large mortality benefit from diagnosis and treatment when compared with the small risks of CTA. However, given the low prevalence of TAD (~ 0.05% among emergency department patients presenting with symptoms previously attributed to TAD), our results suggest that without high-risk features, clinicians should not order a CTA test for TAD. Depending on age, CTA should be considered for those patients with a disease probability greater than 0.3% to 2.1%, whereas d-dimer testing is appropriate in the range of pretest probabilities from 0.01% to 0.6%. Future studies should focus on clinical decision rules that place disease probabilities below, between, and above the calculated TTs.