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How diseases get defined, and what that means for you

We wanted to know about the people who decide where to draw the line between “normal” and “abnormal”, between healthy and diseased. Shutterstock

Have you ever wondered how diseases get defined?

How “high” does your blood pressure have to be before it’s called “high blood pressure”? How “low” does bone density have to be before it’s “osteoporosis”? How big does the “deficit” have to be before a small child is labelled as having “attention deficit disorder”?

Most people would rarely give these questions much thought, but for some of us nerdy researcher types, they’re fascinating.

Why ask?

Last year, a team of colleagues and I based at Bond University designed a study to examine the expert panels that review and change the definitions of diseases. These are the definitions used by your doctor to diagnose and label you and your loved ones.

We wanted to find out a little more about the people who actually gather around a table somewhere and decide where to draw the line between “normal” and “abnormal”, between healthy and diseased. We focused in on panels in the United States because of their global influence in the world of medicine.

In particular, we wanted to know how often these groups tended to widen or expand the boundaries of disease and classify more people as patients.

We also wanted to know whether these expert panels considered the potential dangers of their decision to expand or narrow disease definitions - along with the possible benefits.

And finally, we wanted to know how many of the people who were publishing proposals to change disease definitions had financial relationships with pharmaceutical and device companies.

Mapping overdiagnosis

The background to the study was our interest in the problem of “overdiagnosis” – the subject of a series of articles on this website, and newly launched series in one of the world’s leading medical journals, the BMJ.

Overdiagnosis happens when people are given a label for a condition – and potentially treated for it – when that condition would never have harmed them. Their treatment might offer no benefit at all.

The problem is driven by many different factors – legal, commercial and technological – but also by widening disease boundaries, which catch more and more people with milder symptoms or those who are at low risk of future disease.

The other context for the study was concern about the financial entanglement between doctors and drug companies.

A 2009 report from the influential Institute of Medicine (part of the National Academies of Science in the United States) found:

widespread relationships with industry have created significant risks that… financial interests may unduly influence professionals’ judgments.

And that these “conflicts of interest” threaten the integrity of research, the objectivity of education, the quality of patient care, and public trust in medicine.


While it is well known that these financial ties are widespread, it was not known – until our study – whether the ties extended to the experts who define disease, and decide who among us should be labelled as sick.

What we found

The results of our study on expert panels that make changes to common disease definitions are published today in the open access journal PLOS Medicine.

You can read the full text of the publication yourself, but here are a few key findings in a nutshell. We only looked at 14 conditions, but the list features some very common ones including high blood pressure, high cholesterol, asthma, rheumatoid arthritis and attention deficit hyperactivity disorder (ADHD).

We found that out of 16 different publications from these panels since the year 2000, ten proposed changes to the disease definition in a way that tended to widen the disease boundaries.

One panel created “pre-high blood pressure”, for instance, while another announced “pre-dementia” and several lowered the thresholds that define illness, including the ADHD panel. One panel narrowed the definition of its disease, and in five cases, we were unclear about the impacts of the changes.

About half of the panels made some brief mention of the potential downsides of their proposed changes, but in no case did any panel publication rigorously investigate the potential harms of their decisions to expand a disease and classify more people as sick.

Among all the panels that disclosed members’ financial ties, an average of 75% of panel members disclosed financial relationships with drug companies.

When we looked at the drug companies, we found they were the same companies selling drugs for the diseases those experts were making decisions about. And the relationships were extensive – panel members had ties to a median number of seven drug companies each, often as a consultant or speaker or researcher.

Time to untangle

Our study has limitations that provide context for understanding the results.

Importantly, we had no comparison group. So we made no findings of any causal link between panel members’ decisions to expand disease definitions, and their financial ties to drug companies that stand to benefit.

We also make no judgements on the decisions made by the panels included in our study.

But as we say in our concluding remarks:

findings that diagnostic thresholds are being lowered by panels dominated by those with financial ties to multiple companies that may benefit directly from those decisions raise questions about current processes of disease definition.

We think it’s time to give much more public scrutiny to the way diseases are being expanded, and to design new ways to define them. This may mean new panels of people with minimal or no conflicts of interest, and much broader representation, who will rigorously examine the benefits and potential harms of their decisions.

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