20th September 2026
How Is Alzheimer's Diagnosed? A Short Guide to Tests, Scans, and Treatments
Noticing memory slips in yourself or a loved one can be worrying and one of the first questions people ask is, how is Alzheimer's diagnosed? The good news is that the process for identifying Alzheimer's disease is well established, and getting an accurate Alzheimer's diagnosis through the right tests and scans is the first step towards understanding what's happening and what support is available.
Diagnosis is not a single test but a series of steps, starting with your GP and, where needed, moving on to specialist memory assessments and brain imaging. Here's what that pathway involves.
Alzheimer's, dementia and mild cognitive impairment: what's the difference?
These terms are often used interchangeably, but they mean different things.
- Alzheimer's disease is a form of progressive memory loss that goes beyond the mild forgetfulness that can come with normal ageing.
- Dementia is a broader term for memory disorders serious enough to interfere with daily life. Alzheimer's is the most common cause, but vascular dementia, Lewy body dementia and other conditions also fall under this umbrella.
- Mild cognitive impairment (MCI) describes a milder, in-between stage of memory change that isn't significant enough to be classed as dementia. It doesn't always progress further, but early-stage Alzheimer's can be one of its causes.
Why an early diagnosis matters
Memory loss can have many causes, some of which are easily treatable, so working out what's behind your symptoms matters. Getting an answer early gives you and your family more time to plan, access the right treatment and support, and make informed decisions. In general, the sooner a diagnosis is made, the more control you have over what happens next.
Begin with a GP appointment
A visit to your GP is usually the starting point. Because memory problems can stem from a range of issues, your GP will talk through what you've been experiencing and may carry out tests to rule out other explanations, such as a vitamin deficiency or an underactive thyroid.
If these checks don't explain your symptoms, your GP can refer you to a specialist for further assessment.
Memory assessments and MRI scans
A specialist will typically combine memory and thinking tests with an MRI brain scan to build up a clearer picture of what's going on.
The MRI scan doesn't just look for signs of Alzheimer's, it also helps rule out other causes of memory problems, such as a previous stroke, narrowing of the blood vessels supplying the brain, or general brain shrinkage. It can sometimes show changes consistent with Alzheimer's, but its main value is often in excluding other conditions.
What are the specialist tests for confirming Alzheimer's disease?
Alzheimer's disease is linked to a build-up of a sticky protein in the brain called amyloid. Two tests can detect this directly:
- A lumbar puncture (spinal tap), which analyses spinal fluid and can pick up signs of amyloid at an earlier stage, though it does involve a short procedure.
- A specialised PET scan, which comes in two types: an FDG PET scan, which looks at how active different areas of the brain are, and an amyloid PET scan, which detects the amyloid protein directly.
These scans usually require insurance approval in advance, and it can take a few months to get an appointment, so it's worth discussing timelines with your specialist early on.
Geriatric Medicine
The aim of geriatric medicine is to prevent and treat diseases and improve quality of life. The service is provided by geriatricians who specialise in caring for older adults, especially those with complex medical needs.
Learn more
What about blood tests?
You may have seen news coverage of new blood tests that can detect Alzheimer's disease. While research in this area is moving quickly, these tests are not yet part of routine clinical practice in Ireland. They're expected to become more widely available soon, initially to help identify people with a clear diagnosis or those who need further tests to confirm one.
Why diagnosis matters for treatment options
A confirmed diagnosis also determines which treatments are available to you. Established medications such as donepezil or memantine can help manage symptoms for many people with Alzheimer's. More recently, newer drugs such as lecanemab and donanemab have become available in Ireland; these work differently, targeting the amyloid protein itself and helping to slow disease progression in the earliest stages.
These newer treatments aren't suitable for everyone. Strict eligibility criteria apply, covering factors such as disease stage, confirmed amyloid, gene testing and other medications you may be taking. Your specialist can talk you through these criteria and whether you might be a candidate.
At present, lecanemab and donanemab are available in Ireland only on private prescription, through specialised hospital clinics equipped to manage infusions and the required monitoring scans. They are not funded by the HSE or by health insurers.
What can you do to support your brain health?
Whether or not new medications are an option for you, daily habits can make a difference. Research shows that managing lifestyle risk factors can prevent or delay up to almost half of all dementia cases.
High blood pressure, high cholesterol and diabetes all affect blood supply to the brain, so it's worth keeping these well controlled. By staying physically active you are encouraging healthy brain cell connections. Hearing loss that isn’t treated makes the brain work much harder to process sound and can lead to cognitive decline. Remaining social, eating well, and having a consistent sleep schedule are also positive lifestyle traits to support brain health.
What to expect next
If you or a family member are noticing persistent memory slips, difficulty finding words, or other changes in day-to-day thinking, the right first step is to book an appointment with your GP. They can carry out initial checks and, if needed, refer you on to a specialist memory clinic or consultant geriatrician for a full assessment.
The above content is based on an article written by Dr. Shane O'Hanlon, Consultant Geriatrician at Mater Private Network in Dublin.
.jpg?sfvrsn=51b28ca9_1)
