When psychiatrists assess the same patient, they agree on the diagnosis in only about half of cases, according to a new study.

The findings raise concerns about potential misdiagnosis, inappropriate treatment, and errors in psychiatric research.

In the 1970s, psychiatric diagnoses were marked by considerable uncertainty and disagreement. Since then, organizations such as the American Psychiatric Association and the World Health Organization (WHO) have worked to develop standardized diagnostic criteria that psychiatrists around the world can use.

“We consider that worryingly low.”

These efforts have shaped modern psychiatry by establishing common, criteria-based systems for diagnosing mental disorders across institutions and national borders.

However, a new study, led by researchers at the University of Copenhagen, suggests that major challenges remain. In the study, 1,038 psychiatrists and physicians working in psychiatry from 19 countries were presented with nine written patient case descriptions. Each participant was assigned two cases and asked to determine the most appropriate diagnosis.

The results surprised the researchers.

“Our study shows that when two psychiatrists diagnose the same patient, they will agree only 55% of the time. We consider that worryingly low. In fact, it is similar to the levels reported in some of the studies conducted in the 1970s, which prompted the development of standardised diagnostic criteria in the first place,” says Professor and Consultant Psychiatrist Julie Nordgaard.

“This is not about psychiatrists doing a poor job. Rather, it reflects the fact that, despite the existence of diagnostic systems, clinicians continue to differ in how they interpret symptoms and which features they consider most important. We need a greater degree of consensus, otherwise patients risk receiving changing diagnoses and treatments,” she adds.

The study found substantial variation in diagnostic agreement across different mental disorders. Diagnoses within the schizophrenia spectrum proved particularly challenging.

“Cases that could be diagnosed either as schizophrenia or schizotypal disorder generated especially high levels of disagreement. In many of these cases, agreement among participants was well below 50%,” says PhD candidate Mateo Boberg, the study’s first author.

According to Boberg, one reason is that symptoms frequently overlap across psychiatric disorders. For example, obsessive thoughts may occur in both obsessive-compulsive disorder (OCD) and schizophrenia.

“These are not random errors. There is a clear pattern to the disagreements. This likely reflects the fact that diagnostic categories are not as clearly defined as we have assumed, when experienced psychiatrists can interpret the same symptom presentations so differently.”

Disagreement about diagnoses is an obvious concern for patients. But the researchers argue that diagnostic uncertainty also threatens the reliability of some kinds of psychiatric research, explains Professor Mads Gram Henriksen:

“In research, it is essential that we know exactly what we are studying. If a considerable part of participants enrolled in a study on treatment of personality disorders actually suffer from schizophrenia, the study’s results become difficult to interpret. Which condition is the treatment having—or not having—an effect on? Personality disorders or schizophrenia?”

The researchers argue that progress in psychiatric research risks remaining limited until there is a clearer and more widely shared understanding of what mental disorders are and how they can be distinguished from one another. Greater diagnostic agreement, they say, is a prerequisite for the breakthroughs needed to improve patient care.

“WHO’s ICD-10 diagnostic system, which participants in the study used to assess the cases, contains more than 200 diagnoses, a complexity that may contribute to uncertainty. At the same time, many psychiatric conditions are inherently multifaceted,” says Nordgaard.

“In our view, it is necessary to take a step back and develop more precise descriptions of psychiatric disorders so that clinicians can distinguish them more clearly. It may also be necessary to reduce the number of diagnostic categories.”

The study appears in Frontiers in Psychiatry.

• 1,038 physicians from 19 countries in Europe and South America participated in the study. All worked in adult psychiatry.
• Each participant was assigned two of nine standardised written clinical cases and asked to select a diagnosis using the WHO ICD-10 diagnostic system.
• Researchers measured both agreement between clinicians and the frequency with which they selected the reference diagnosis.
• Overall diagnostic agreement was 55%.
• Diagnostic variability was significantly higher for schizophrenia and related conditions compared to other disorders.
• Diagnostic accuracy was lowest for schizophrenia and related disorders (37–54%) and highest for bipolar disorder (94%) and obsessive-compulsive disorder (92%).
• No significant differences were found between more experienced and less experienced clinicians, suggesting that disagreement cannot be explained by variations in professional experience.

Source: University of Copenhagen