Letter to the Editor: “Did medical doctors who order abdominal CT scans during on-call hours truly become worse at clinical reasoning? Yes, they did”

by Jonne J. Sikkens, Abel Thijs (j.sikkens@amsterdamumc.nl)

Did medical doctors who order abdominal CT scans during on-call hours truly become worse at clinical reasoning? Yes, they did

Dear Editor,

We read with great interest the recent article by Arsoydan et al: “Did medical doctors who order abdominal CT scans during on-call hours truly become worse at clinical reasoning? Yes, they did” [1]. As internists, we practice clinical reasoning on a daily basis so we really appreciate the authors’ initiative to investigate this in practice. While the study adds valuable insights, we disagree with the overall conclusion as stated in the title.

Our main objection is that the authors did not actually measure an operationalization of clinical reasoning quality, but rather the concordance between differential diagnoses on CT request forms and CT results. Although this may correlate with clinical reasoning quality, it is not necessarily related to this process, which means that there are many perfectly valid alternative explanations for the authors findings. The most likely explanation for the decrease in concordance is the simultaneous increase in CT scans, inversely mirroring the concordance trend (see figure 2 in the original article) [1]. If we assume that the absolute amount of pathology presented to the hospital is more or less stable, which seems reasonable, the concordance between the request forms and CT scans must go down as a matter of mathematical certainty [2]. After all, performing more scans in the same number of patients from similar populations must result from scanning with a lower prior probability of disease. This in turn leads to a lower scan yield and therefore a lower concordance. Adjusting for the number of performed CT scans in their regression model could alleviate this problem so we invite the authors to perform this analysis and share their results.

Unfortunately, this correction does not resolve all problems with the study design. Other alternative explanations for a lower concordance include the fact that the increased availability of CT scans lessens the need for physicians to make an effort in accurately supplying their differential diagnoses in the CT request form, so the form does not necessarily equate their thinking.

If the decrease in concordance can indeed be fully explained by the increased number of CT scans, this does not make the findings lose all merit, as too liberal use of CT scans is a phenomenon worth discussing.

P.S.: For illustration purposes, we made an online calculator to demonstrate the relation between CT scan willingness and CT scan positivity: link.