Patients' preferences are often misinterpreted or ignored in treatment decisions, leading to a "silent misdiagnosis" that is damaging to both doctors and patients, warn experts on bmj.com today.

Albert Mulley from The Dartmouth Center for Health Care Delivery Science in the USA, along with Chris Trimble and Glyn Elwyn, a visiting professor there from Cardiff University in Wales, argue that a doctor cannot recommend the right treatment without understanding how the patient values the trade offs.

Making an accurate medical diagnosis remains a source of professional pride for many physicians, say the authors, yet evidence suggests that the problem of "preference misdiagnosis" is high.

For example, there are often gaps between what patients want and what doctors think they want. In one study, doctors believed that 71% of patients with breast cancer rate keeping their breast as a top priority, but the figure reported by patients was just 7%. And in a study of dementia, patients placed substantially less value than doctors believed on the continuation of life with severely declining cognitive function.

Evidence also shows that patients often choose different treatments after they become better informed about the risks and benefits, say the authors. One study found that 40% fewer patients preferred surgery for benign prostate disease once they were informed about the risks of sexual dysfunction.

Ensuring patients' preferences are not misdiagnosed is not as simple as asking the patient what he or she wants, explain the authors. Instead it requires three steps: adopting a mindset of scientific detachment; using data to formulate a provisional diagnosis; and engaging the patient in three steps of shared decision making: team, option and decision talk.

Better diagnosis of patients' preferences is not only the right ethical thing to do but it may also reduce the cost of healthcare, they add, as evidence from trials shows that engaged and informed patients often choose to have less intensive care and to become more careful about having lots of procedures.

More work is needed to understand whether these potential benefits could be realised in healthcare systems, they conclude, "but it is tantalising to consider that budget challenged health systems around the world could simultaneously give patients what they want and cut costs."