Paying patients to forgo head CT (Iyengar 2019)

Paying patients to forgo head CT

Although the CT scan is a wonderful piece of technology that has undoubtedly improved the practice of emergency medicine, we are clearly over-using this technology in modern practice. For example, one study that looked retrospectively at all head CTs ordered for trauma concluded that more than 1/3 were unnecessary based on the Canadian CT head rule. (Sharp 2017) As part of the SGEM Hot Off the Press series, Ken and I looked at an interesting paper that considered the impact of offering low risk patients money to forgo head CT…

The paper

Iyengar R, Winkels JL, Smith CM, Meka AP, Porath JD, Meurer WJ. The Effect of Financial Incentives on Patient Decisions to Undergo Low-value Head Computed Tomography Scans. Academic emergency medicine. 2019; 26(10):1117-1124. PMID: 31535430 [free full text]

The Methods

This is a survey based randomized, controlled trial based on a hypothetical clinical scenario.


A convenience sample of adult patients presenting to the University of Michigan emergency department.

  • Exclusions: Patients with chest pain or head trauma (because those were the conditions in the hypothetical cases presented). They also excluded patients with altered mental status, with contact precautions, or in resuscitation bays.

Intervention and comparison

Patients were all presented with a hypothetical low risk head trauma scenario. The scenario was designed such that the Canadian Head CT rule suggests against imaging. Three aspects of the scenario were randomized:

  • Benefit: This was presented as either 1% or 0.1%
  • Risk: This was presented as either 1% or 0.1%
  • Incentive: Patients were offered either $100 to forgo the CT or $0.
    • All risk and benefit information was provided in multiple formats, including percentages (0.1%), ratios (1 in 1,000), and visual depictions.


The primary outcome was the percentage of patients who chose to receive a CT scan.

The Results

They enrolled 913 patients. The median age was 45 and 56% of the population was female. The vast majority of this population identified as Caucasian and had attended at least some college. Overall, 54.2% of patients elected to receive a CT scan. As you might expect, decreased benefit, increased risk, and offering a cash incentive to forgo CT all decreased the desire for CT.

  • If the benefit was reported as 0.1% then 49.6% of people wanted a CT, whereas if it was 1% then 58.9% wanted a CT (OR 1.48 95% CI 1.13 – 1.92).
  • If the risk was reported as 0.1% then 59.3% of people wanted a CT, whereas if it was 1% then 49.1% wanted a CT (OR 0.66 95% CI 0.51-0.86).
  • If no cash incentive was offered then 60% of people wanted a CT, whereas if 100$ was offered to forgo the CT then 48.3% of people wanted a CT (OR 0.64 95% CI 0.49-0.83).

My thoughts

Obviously, there are some problems with extrapolating the results of a hypothetical scenario to real world practice. It is even more difficult to extrapolate these results to other practice settings. Despite being low risk and not requiring imaging according to the Canadian CT had rule, more than half of the patients still wanted a CT. Where I work (both in Canada and New Zealand), these patients wouldn’t have even been offered a CT scan. (Although, to be fair, these patients were presented with risk and benefit numbers that are somewhat different than the low risk group in the Canadian CT head rule trials.) There is a full critical appraisal that covers these issues and more over on the SGEM website and podcast.

There was one number in this trial that really stood out to me. In the group of patients who were told that the benefit of CT was 0.1% and the harm was 1%, 50% still wanted a CT scan. They were explicitly told that harm was 10 times more likely than benefit, and half still wanted a CT! That number is absolutely shocking.

Why would anyone want a test that results in more harm than benefit? It is possible that, despite the authors’ excellent attempts to describe the harms and benefits in multiple formats, the participants still didn’t understand the numbers. Despite our best efforts to use language that patients understand, there is little doubt that miscommunication is still common between physicians and their patients. 

The shocking statistic might also be a consequence of the qualitative differences between the harms and benefits. Harms from radiation won’t crop up for decades, while the benefits are much more immediate. These differences in harms and benefits are why evidence based medicine must always involve clinician judgement and patient preference, in addition to the best available clinical evidence. (Sackett 1996)

Ultimately, I think this number provides important insight into the limits of shared decision making. If the harms of a test clearly outweigh the benefits, it shouldn’t be offered. Patient satisfaction should not overrule good medical care. Our responsibility as doctors sometimes involves protecting patients from themselves. (We also need to protect patients from ourselves and overzealous guidelines by, for example, avoiding stress tests or heparin for NSTEMI.)

Shared decision making is a wonderful tool when there is truly equipoise. It should be used when the harms and benefits are evenly matched. It should be used when the harms and benefits are qualitatively different, requiring a judgement call in priorities. It should be used when there is significant uncertainty about the actual harms and benefits. However, it shouldn’t be used when one option is clearly better than another.

In my mind, money doesn’t seem to fit into this framework. In offering cash to forgo a CT scan, we are implying that the no testing option is clearly better than the testing option. We believe so strongly that forgoing CT is the right thing to do that we are willing to offer patients money to choose that option. But if that is the case, shared decision making has no role. Just don’t order the test.

If, on the other hand, you believe that there is a reasonable choice to make between two options – that patients with different value systems will choose differently – it doesn’t seem appropriate to try to influence those decisions with cash incentives. The shared decision making process is grounded in a respect for patients’ values and opinions. Why even start that process, if you are just going to pay patients to do what you want?

I can think of counter-examples. Human behaviour is far from rational and financial nudges can be effective motivators. It might make sense to pay patients not to smoke. Society might decide to shape eating habits through selective taxation. I am not against the idea of using financial incentives to change behaviour or improve health.

However, it seems very different in the context of a clinical decision. It seems to undermine the concept of shared decision making; to make shared decision making more about covering the doctor’s ass than truly engaging with the patient about their values. In my sleep deprived state, I can’t seem to put my finger on the exact dividing line, but I just don’t see the need for financial incentives in my practice. I think a simple description of the harms and benefits, followed by a two-sided, engaged discussion exploring how those harms and benefits fit in the patient’s life is enough. We don’t need to complicated matters with financial rewards.

Bottom line

I can’t imagine that I will be offering my patients financial incentives as part of medical decision making any time soon. Also, I sincerely hope that we aren’t scanning 50% of patients who pass the Canadian CT head rule

Although not practice changing for me, I think this paper raises a number of fascinating questions. I would love to hear your questions or comments. You can leave them in the comments section below, or join the conversation on the SGEM website or on Twitter using #SGEMHOP.

Other FOAMed



Iyengar R, Winkels JL, Smith CM, Meka AP, Porath JD, Meurer WJ. The Effect of Financial Incentives on Patient Decisions to Undergo Low-value Head Computed Tomography Scans. Academic emergency medicine. 2019; 26(10):1117-1124.

Sackett DL, Rosenberg WM, Gray JA, Haynes RB, Richardson WS. Evidence based medicine: what it is and what it isn’t. BMJ (Clinical research ed.). 1996; 312(7023):71-2. [pubmed]

Sharp AL, Nagaraj G, Rippberger EJ, et al. Computed tomography use for adults with head injury: describing likely avoidable emergency department imaging based on the Canadian CT Head Rule. Acad Emerg Med 2017;24:22–30.

Cite this article as:
Morgenstern, J. Paying patients to forgo head CT (Iyengar 2019), First10EM, October 31, 2019. Available at:

Title photo by Michael Longmire on Unsplash

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