Letters
Emergency medicine Medical practices
Volume 200 - Issue 1

Changing trends in venous thromboembolism-related imaging in Western Australian teaching hospitals, 2002–2010

Authors:  William B G Macdonald and Tatiana Segard

Med J Aust 2014; 200 (1): 27. || doi: 10.5694/mja13.11245
Published online: 20 January 2014
In reply: We thank Mountain for his comments. As he points out, it is only possible to infer cause and effect from observational data. The fact that referrals for D-dimer levels and computed tomography pulmonary angiography increased during the same period does not prove that one “drove” the other, although we believe this is a reasonable inference. Importantly, D-dimer testing was introduced as a “rule-out” ...
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In reply: We thank Mountain for his comments. As he points out, it is only possible to infer cause and effect from observational data. The fact that referrals for D-dimer levels and computed tomography pulmonary angiography increased during the same period does not prove that one “drove” the other, although we believe this is a reasonable inference. Importantly, D-dimer testing was introduced as a “rule-out” test in low-risk patients, in an effort to reduce unnecessary referrals for venous thromboembolism imaging; but we found no evidence in our observational data that this had occurred.

We agree with Mountain’s alternative hypothesis that “new tests that were perceived as useful increased investigation rates” and believe our data showed precisely this. The critical issue, however, is whether perceived usefulness equates to actual usefulness (ie, improved outcomes) or simply results in overdiagnosis.1 Our data, and that of others,1,2 suggest the latter is more likely. This is a worthy topic for further research, particularly as D-dimer testing is now routine in the investigation of patients with potential thromboembolism in most Australian hospitals.

When reviewing statewide mortality from pulmonary embolism, we are comfortable that statewide census data are the appropriate measure of growth for the at-risk population.

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