Fundamentals of psychiatric diagnosis

by TheEditor

Categories: Investigative, Mental Health

Back in the 1990s, diagnostic criteria existed for sure. We had ICD-9 as our main diagnostic manual. My recollections from around that time was that the criteria were hardly ever referenced. How it worked was, the consultant psychiatrist would declare diagnosis or differential diagnoses without actually stating which criteria were met from available evidence. As a junior trainee, I had no say in the matter. In one adolescent psychiatry service around 1993, the consultant psychiatrist and a consultant psychologist stated, “We do not deal with diagnoses.” That happened when I attempted to refer to the diagnostic criteria for a patient who I thought had a conduct disorder. I had to shut up, else risk being ‘marked down’ as a ‘difficult to supervise’ trainee. That sort of thing was never a verbalised threat, but one knew that the probability existed.

Advent of ICD-10

ICD-10, drawing on much international research, was published around 1990 but was only adopted by this profession a few years later. Such was the pace of change. The delay was somewhat understandable because we only had physical books in that decade and information did not fly around as it does today with the ‘information superhighway’ (aka internet). My experience between 2000 and 2010 informed me that many psychiatrists still did not conspicuously match clinical evidence to diagnostic criteria in ICD-10. The word ‘evidence’ is repeated many times in ICD-10 Diagnostic Classification of Mental and Behavioural Disorders. What I saw happening quite widely, was a feeling about the evidence, not the finding of the evidence. In other words ‘opinion evidence‘ without tangible objective evidence mattered more.  That never sat well with me. In one occasion around 2010, I observed a patient who was a prisoner, being diagnosed by a psychiatric expert acting for the courts with personality disorder, after approximately 45 minutes of interview time.  There was no matching of the evidence to the criteria in the report. That was to be played out in several other similar scenarios over the next decade. I’ve now studied hundreds of psychiatric reports to courts and Tribunals, and read tens of thousands of pages of running records, over the last 30 years, My experience is clear.

Importance of psychiatric diagnosis

Whilst diagnostic reliability is essential, so is validity (the accuracy of the diagnosis, i.e., whether it correctly identifies the presence or absence of a disorder). A diagnostic system could be reliable (consistently applied) but not valid (accurately identify the disorder). Both reliability and validity are crucial for effective psychiatric care. Here are some important issues about diagnosis:

  1. Treatment planning: Reliable diagnosis is critical for determining the most effective treatment plan for a patient. The choice of medication, therapy type, and other interventions largely depend on the specific diagnosis. An incorrect or unreliable diagnosis can lead to inappropriate or ineffective treatment, potentially causing harm or leading to a delay in symptom improvement.
  2. Prognostic implications: Different psychiatric diagnoses often have different prognoses. A reliable diagnosis can help in predicting the course of the illness and planning accordingly, both in terms of treatment and lifestyle adjustments.
  3. Communication among professionals: A reliable diagnosis provides a common language for healthcare professionals. When a psychiatrist gives a diagnosis, other professionals (like psychologists, social workers, nurses, and primary care doctors) should have a clear understanding of what that diagnosis implies regarding symptomatology, expected course, and treatment approach.
  4. Reimbursement: In many healthcare systems, a diagnosis is required for insurance reimbursement for services. If the diagnosis is unreliable, it may lead to disputes over coverage, creating additional challenges for the patient and the provider.
  5. Legal context: In legal situations, such as determining eligibility for disability benefits or assessing fitness to stand trial, reliable diagnoses are crucial.
  6. Patient understanding and stigma: A reliable diagnosis can aid in patient understanding of their condition and in validating their experiences, which can be therapeutic in itself. It also helps in combating stigma, as it underscores that psychiatric disorders are legitimate medical conditions.
  7. Research consistency: Reliable diagnoses are essential for research. They ensure that study populations are comparable across different research projects, which is key to advancing our understanding of psychiatric disorders.


The complexity of psychiatric diagnoses has increased over the last decade due to a number of factors. These can be grouped into several broad categories:

  1. Scientific advancements: Advances in our understanding of mental health conditions have led to more nuanced definitions and classifications. This can make diagnosis more complex, as there are now more conditions to consider and a wider range of symptoms and presentations to recognise. Furthermore, we now know that psychiatric conditions often overlap and that many people have more than one mental health condition.
  2. Societal changes: There is increasing recognition of the importance of mental health, which has led to more people seeking help for mental health issues. This increases the diversity and complexity of cases that psychiatrists see. Additionally, societal changes such as the digital revolution have led to new phenomena like “digital addiction”, which have added to the complexity of mental health diagnoses.
  3. Changes in healthcare delivery: There have been significant changes in the healthcare system, including the introduction of more structured diagnostic criteria and clinical guidelines. For example, diagnostic criteria like the DSM-5 and ICD-10/ICD-11 have become more complex and nuanced over time, reflecting our improved understanding of mental health conditions but also adding to the complexity of diagnosis.
  4. Patient expectations: Patients are now more likely to have researched their symptoms online before seeking help, which means they may come to a consultation with specific diagnoses in mind. This can make the diagnostic process more complex, as psychiatrists need to manage these expectations and ensure they do not overlook potential diagnoses.
  5. Technological innovations: The advent of new diagnostic tools and technologies, such as neuroimaging and genetic testing, have the potential to add further complexity to psychiatric diagnosis. These tools can provide valuable information, but their interpretation and integration into the diagnostic process can be challenging.
  6. Multidisciplinary approach: Modern psychiatric practice often involves a multidisciplinary team, including psychologists, social workers, occupational therapists, and others. This approach allows for a more holistic view of the patient’s condition but also requires coordination and communication among team members, adding another layer of complexity.
  7. Biological markers and precision medicine: While we are still in the early stages of understanding the biological basis of psychiatric disorders, there’s a growing interest in identifying biomarkers and adopting a precision medicine approach to mental health. This could lead to more personalised and effective treatments but also adds another layer of complexity to diagnosis.
  8. Comorbidity: Comorbidity, the presence of one or more additional conditions co-occurring with a primary condition, is common in psychiatric disorders. This often complicates diagnosis, treatment, and management, as different conditions may have overlapping symptoms and may require different treatment approaches.

In summary, while the process of diagnosing mental health disorders has become more complex, these changes reflect advances in our understanding and treatment of these conditions. The challenge is to ensure that this complexity is managed effectively so that it benefits patients and contributes to improved mental health outcomes.

Diagnostic process

When I say that I am the only psychiatrist I know who would demonstrate the matching of evidence to criteria that would be true and not boasting at all. The following is what I do, and what I think every psychiatrist should do.


  1. Initial patient assessment: This usually involves a clinical interview where the psychiatrist gathers detailed information about the patient’s symptoms, history, and overall mental health. This includes understanding the severity, duration, and frequency of symptoms.
  2. Use of diagnostic criteria: The psychiatrist then refers to the relevant diagnostic manual (DSM or ICD) and uses it as a reference to compare the patient’s reported symptoms and behaviours. The psychiatrist will check if the symptoms align with the listed criteria for potential diagnoses.
  3. Rule out other causes: It is important to determine whether the symptoms could be better explained by another mental or physical health disorder, or whether they could be the side effects of a medication or substance use. Psychiatrists also need to rule out any potential mimicking conditions.
  4. Assessing impairment and distress: Diagnosis typically requires that the symptoms cause significant distress or impairment in social, occupational, or other areas of functioning.
  5. Seek multidisciplinary team perspectives: In many cases it is important to seek perspectives that may assist from psychologists, nurses, social workers, occupational therapists and pharmacists. This is not asking them ‘what they think they diagnosis is’. It is important when working within the biopsychosocial model to evaluate how symptoms, signs and behavioural patterns become prominent. Some psychological symptoms may have roots in psychosocial stress – and could be transient our coloured by those circumstances.
  6. Establishing a diagnosis: If the symptoms match the criteria for a specific disorder and there’s significant impairment or distress, the psychiatrist may arrive at a diagnosis.
  7. Differential diagnosis: If symptoms meet criteria for more than one disorder, the psychiatrist must decide which diagnosis most accurately represents the patient’s condition. This often involves considering which diagnosis best explains the majority of symptoms, or which disorder is most impairing.
  8. Review and monitor: Diagnoses may change over time as symptoms evolve or new information becomes available. Therefore, regular review and monitoring is important.


Diagnosis ought not to be static i.e. once done forgotten about or etched in stone. Sometimes a patient’s symptoms or signs may change. Diagnosis may not be ‘one thing’. In personality disorders, depressive illnesses, or psychoses, it may be difficult to pin down exactly which one. This happens because there may be an overlap of symptoms and signs in the criteria. The patient’s problems often do not fit easily into categories.

On some occasions the evidence relied upon may be discovered to be unreliable at a later stage.

Reliability in psychiatric diagnosis refers to the consistency or reproducibility of a diagnosis when the same patient is assessed by different clinicians or by the same clinician at different times. Several factors can influence the reliability of psychiatric symptoms and signs:

  1. Quality of the clinical interview: The quality of the information obtained during the clinical interview is crucial. If a clinician doesn’t ask the right questions or if a patient isn’t forthcoming or accurate in their responses, it can lead to unreliable findings.
  2. Patient factors: The reliability can be affected by factors specific to the patient. For example, a patient’s willingness to disclose information, their insight into their condition, and their memory and understanding of their own experiences can all influence reliability.
  3. Clinician factors: Clinician factors include the skill, experience, and expertise of the clinician, as well as any preconceptions or biases they might have. Different clinicians may interpret the same information differently, which can affect the reliability of the diagnosis.
  4. Cultural factors: Cultural factors can also influence reliability. Symptoms of mental disorders can vary widely across different cultures, and what is considered “normal” behaviour in one culture might be seen as symptomatic in another.
  5. Temporal factors: Mental health symptoms can fluctuate over time, and what is present at one assessment may not be present at another, affecting the reliability of diagnosis.
  6. Use of assessment tools: The use of structured or semi-structured assessment tools can increase reliability by providing a standard format for collecting information and making diagnoses.
  7. Severity and stage of the disorder: The severity of the illness, its duration, and the stage at which it is being evaluated can also influence the reliability of symptoms and signs. For instance, early in the course of a disorder, symptoms may be more subtle and harder to reliably detect.

Improving reliability in psychiatric diagnosis is an ongoing challenge. However, using structured diagnostic tools, enhancing clinician training, ensuring cultural competence, and including input from multiple sources (such as family members or other healthcare providers) can help increase reliability.

Reflections and summary

The complexity of psychiatric diagnoses has increased significantly over the past decade due to scientific advancements, societal changes, changes in healthcare delivery, patient expectations, and technological innovations. This complexity often requires a more time-consuming process than was typical two decades ago, largely because of the need for a thorough evaluation, the high prevalence of comorbidity in psychiatric disorders, the use of a multidisciplinary team approach, and the demands of documentation and regulatory requirements.

In the diagnostic process, psychiatrists utilise diagnostic criteria such as those found in the Diagnostic and Statistical Manual of Mental Disorders (DSM) or the International Classification of Diseases (ICD). These criteria provide standardised definitions for various mental disorders, but the art of diagnosis also lies in the psychiatrist’s clinical judgment, experience, and understanding of the patient’s unique context. Multidisciplinary teamwork becomes important in many cases, so as to avoid over-medicalisation of patients.

Reliability in psychiatric diagnosis is crucial, as it refers to the consistency or reproducibility of a diagnosis when the same patient is assessed by different clinicians or by the same clinician at different times. Factors influencing reliability include the quality of the clinical interview, patient and clinician factors, cultural considerations, temporal factors, the use of assessment tools, and the severity and stage of the disorder.

Reliable psychiatric diagnosis is of paramount importance for treatment planning, prognostic implications, research consistency, communication among professionals, insurance reimbursement, legal contexts, and patient understanding and stigma reduction. While diagnostic reliability is essential, so is validity—the accuracy of the diagnosis. Both reliability and validity are crucial for effective psychiatric care.

It was standard in the 1990s for psychiatric diagnoses to be made by a psychiatrist within an hour of seeing a patient. Many psychiatrists still work within the unwritten one-hour rule. I find it difficult to be fair to patients to carry out the diagnostic process within one hour given all the demands for quality and standards, that have emerged over the last 10 years.

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