How Dementia Is Diagnosed: The Tests Explained, and Why It Can Take So Long

A quiet note before you read on: if you've just had a diagnosis, or you're waiting for one, this can be a disorientating time. Take this in at whatever pace feels right — there's no rush to understand it all at once.

There's no single test for dementia

That surprises a lot of people. A diagnosis isn't one scan or one score — it's built from several assessments over time, usually starting with your GP and, if needed, moving on to a specialist memory clinic.

The usual first step: your GP

If you're worried about your own memory, or someone else's, the starting point is a GP appointment. They'll typically:

• Ask about your symptoms and how they're affecting daily life
• Check whether other conditions (like depression, thyroid problems, or vitamin deficiencies) could be causing similar symptoms — these are sometimes reversible, which is why ruling them out matters
• Review any medications you're taking
• Do a brief cognitive test — a series of simple questions and tasks that check memory and thinking

It genuinely helps to bring someone who knows you well. They can describe changes you might not notice yourself, and help you remember what's said in the appointment afterwards.

If it goes further: the memory clinic

If your GP thinks more investigation is needed, they'll refer you to a memory clinic — usually part of a hospital, staffed by specialists such as old-age psychiatrists, geriatricians, or neurologists.

Waiting times vary a lot by area — anywhere from a few weeks to several months, depending on where you live.

At the memory clinic, you may be offered:

• A more detailed cognitive test — most commonly the ACE-III (see below)
• A brain scan — usually a CT or MRI. This helps rule out other causes and can show changes in brain structure linked to some types of dementia
• Blood tests, if not already done
• Less commonly, a lumbar puncture — this measures certain proteins in the fluid around the brain and spinal cord, and can support a more specific diagnosis in some cases. It's not offered to everyone, and whether it's suggested depends on your specific situation

What the ACE-III actually involves

The ACE-III (Addenbrooke's Cognitive Examination) is the most widely used cognitive test in UK memory clinics. It's worth understanding what it actually checks, because the name alone doesn't tell you much:

• It's a pen-and-paper test, usually taking 15–20 minutes
• It covers five separate areas: attention, memory, verbal fluency, language, and visuospatial skills (things like copying shapes or reading a clock face)
• It's scored out of 100 — higher scores generally indicate better function
• A score below roughly 82–88 is usually the point at which a clinician starts considering dementia as a possibility, though this isn't a hard cut-off on its own

There's genuinely nothing to revise or prepare for — it's designed to measure how someone functions day to day, not to catch anyone out. Wear glasses or hearing aids as normal, ask for a family member to be present if that would help, and it's fine to pause or stop if it becomes upsetting.

Important: the ACE-III doesn't diagnose dementia by itself, and it can't tell you which type of dementia someone has. It's one piece of a bigger picture — the clinician combines it with your history, a physical exam, blood tests, and often a brain scan before reaching any conclusion. If your result comes back with a "borderline" or unclear score, that's genuinely common, not a sign something's gone wrong with the test.

Why "what stage is it?" doesn't always have a clean answer

This is one of the most common sources of frustration, and it's genuinely not just you — even specialists describe it as difficult to pin down precisely. Dementia affects everyone differently, symptoms don't always progress in a predictable order, and there isn't one universal staging scale used everywhere.

What tends to help more than chasing an exact "stage":

• Writing down changes you notice, and roughly when they started
• Bringing specific, concrete examples to appointments rather than general impressions
• Asking your care team what to expect next, rather than which numbered stage you're at

Why it can take so long — and why that's not your fault, or your GP's

If you're months into this and still don't have a firm diagnosis, you're not alone, and nothing has necessarily gone wrong. A national report from Alzheimer's Society (May 2026) found that, on average across the UK, it takes 3.5 years from first noticing symptoms to getting a diagnosis — including roughly six months of that spent specifically waiting for a memory clinic appointment after a GP referral. Nearly three-quarters of GPs report long waits for diagnosis as a routine part of the system, not an unusual delay.

Why it genuinely takes this long, beyond "the NHS is busy":

• Symptoms build gradually. Many people live with early changes for a year or more before anyone — including themselves — recognises it as something to raise with a GP
• Reversible causes have to be ruled out first, properly, before dementia is even considered — this alone involves blood tests, medication reviews, and sometimes weeks of waiting for results
• Memory clinic capacity varies hugely by area. Waits of a few weeks in some regions stretch to many months, even over a year, in others — this is a genuine, documented gap in the system, not something specific to your situation
• A confident diagnosis sometimes needs more than one test cycle. If an initial assessment is inconclusive, clinics may recommend repeating it in 6–12 months rather than guessing

If it helps: the wait, however frustrating, doesn't mean nothing useful is happening in the meantime. Writing down changes as they occur, keeping a simple diary, and preparing questions for appointments are all things that genuinely make later assessments more accurate — you're not just sitting idle while the clock runs.

If you're waiting for an appointment

Waiting is hard, especially with a driving licence in the picture — if a diagnosis is confirmed, there's a legal duty to inform the DVLA (we cover this in more detail in our driving and dementia guide). While you wait:

• Keep a simple written log of changes and when they happen
• Note down any medications, recent hospital stays, or surgeries — the clinic will likely ask
• Write down your questions in advance; it's easy to forget them in the moment

Sources: NHS — Tests for diagnosing dementia, Alzheimer's Research UK, Alzheimer's Society national diagnosis and treatment pathway report (May 2026).

You don’t have to navigate it alone. If things feel overwhelming right now, Admiral Nurses (via Dementia UK) offer free specialist support, and Carers UK has a helpline for practical and emotional support.