Can psychologists make a diagnosis? Yes, but that's not the real question

One of your clients asks you to write a report confirming their diagnosis. Can you do it?

This comes up all the time in supervision. I want to unpack the question, and the assumptions underneath it.

Are you qualified? Of course

If you are a registered psychologist in Australia, assessment, including diagnosis, is a core competency of your registration. You have the training, the expertise and the tools.

But sometimes your diagnosis isn’t good enough. That has less to do with your skill and more to do with politics, history and what diagnosis actually means.

Describing disease versus explaining it

There are two ways to understand an illness.

Nosology describes it. Hippocrates and Galen were doing nosology two thousand years ago, with no microscopes and little idea how the body worked. (If you ever want to feel gloomy, read Hippocrates’ case notes: a vivid description of each illness, then a brief note on what day the patient died.)

Pathology explains it. It takes those descriptions and finds the mechanism underneath. We know the pathology of tuberculosis, HIV and cancer.

In mental health, we have almost none. We have nosology. The DSM is a book of descriptions.

The 1980 bargain

In 1980, the authors of the DSM-III faced a problem. Psychiatrists and psychologists couldn’t agree on what caused schizophrenia, trauma or anxiety. They could agree on what those conditions looked like.

So they made a trade. They gave up on cause and validity, and bought reliability: if one clinician says you meet criteria for panic disorder, another clinician looking at the same symptoms should agree.

It was a good deal for research and communication. But it means the DSM tells you nothing about cause, and nothing about treatment.

What diagnosis is good for

• Research. Grouping patients who meet criteria for a disorder helps researchers hunt for mechanisms. But as of today there is no blood test, brain scan or genetic test that positively identifies any DSM disorder.
• Shorthand between clinicians. If I’m heading off on long service leave and refer you a client with major depressive disorder in the context of dependent personality disorder, you get a broad picture of what to expect without a two-page essay.

What it isn’t good for: funding

The DSM was never designed to allocate money. There is no relationship between meeting a DSM or ICD threshold and how much treatment, or funding, a person needs.

Take someone after a serious car accident. The accident covers criterion A. Nightmares and flashbacks: criterion B. They won’t get in a car as driver or passenger: criterion C. Negative beliefs about their role in the accident and their safety on the road: criterion D. But however you ask, there’s no hyperarousal. No jumpiness, no irritability.

Sorry, no PTSD diagnosis. Does that mean their trauma isn’t real, that they don’t need help, or won’t benefit from therapy? Of course not. Yet diagnosis has become a lazy way for insurance assessors to approve or reject claims.

The DSM’s own authors saw this coming. The front of the DSM-5-TR states that “the diagnosis of a mental disorder is not equivalent to a need for treatment”. It goes on to say that people who don’t meet full criteria may still clearly need care, and that this shouldn’t be used to limit their access to it.

Despite that advice from the people who literally wrote the book, diagnosis is used to gatekeep money and treatment: in Medicare, workers’ compensation, insurance and the NDIS.

Reframe the question

For those purposes, the diagnosis itself is close to irrelevant. So the question isn’t “Am I qualified to make a diagnosis?” It’s “Does the person sitting on this pot of money accept my qualifications to make one?”

Some gatekeepers want a clinical psychologist. Some want a psychiatrist, some a GP, and some just accept the label. Reframe the question and the answer becomes pretty clear.

Whether you should give diagnostic opinions for people you treat is a different question, for another day.