How is dementia diagnosed

Dementia diagnosis in brief

A dementia diagnosis is usually based on:

• A detailed history of the symptoms and how they have changed
• Information from a relative or someone who knows the person well
• Assessment of everyday functioning and independence
• Cognitive testing
• Physical and neurological examination
• A review of all medicines
• Blood tests to look for other causes
• Structural brain imaging, usually CT or MRI, when indicated

Specialist investigations such as PET scans, lumbar puncture or biomarker tests are considered only when the diagnosis or the type of dementia remains uncertain and the result is likely to change management.

There is no single test for dementia

Dementia describes a decline in thinking abilities that is significant enough to interfere with everyday life. Memory loss is only one possible symptom. Dementia can also affect language, attention, judgement, visual perception, behaviour, organisation and the ability to carry out familiar tasks.

No questionnaire, cognitive score, blood test or brain scan can confirm or exclude every type of dementia. I interpret each result in the context of the person’s symptoms, previous abilities, education, medical history and day-to-day functioning. A normal cognitive test or brain scan does not always exclude dementia, and an abnormal score or scan does not establish the diagnosis by itself.

Why I assess the whole person, not just memory

Many memory services focus on a single question: is this dementia, and if so, which type? In older adults that question rarely stands alone. Memory and concentration are often made worse by medicines, low mood, poor sleep, hearing or visual loss, pain, infection, heart and circulation problems, falls and frailty. Several of these are treatable.

As a consultant geriatrician, I assess memory within a Comprehensive Geriatric Assessment: a structured review of physical health, medicines, mood, mobility, function and social circumstances. This means the diagnosis is more accurate, reversible contributors are not missed, and the plan that follows addresses the whole person rather than the memory score alone.

What does a dementia assessment involve?

1. A detailed clinical history

I begin by establishing:

• Which symptoms have developed, and when they started
• Whether the changes were gradual, sudden or fluctuating
• How the symptoms have progressed
• Which areas of thinking have been affected
• Whether mood, anxiety, sleep or behaviour have changed
• Whether there are hallucinations, delusions or changes in personality
• Whether the person has become less independent

The pattern and progression of symptoms often tell me more than any single test result.

2. Information from someone who knows the person well

Where the person agrees, I speak to a partner, relative, friend or carer. They may have noticed changes in:

• Repeating questions or forgetting recent conversations
• Managing medicines
• Handling money or paying bills
• Shopping and cooking
• Using household appliances, phones or computers
• Driving and finding the way
• Personal care
• Motivation, judgement or behaviour

This account matters because some people do not recognise the extent of their own difficulties.

3. Assessment of everyday functioning

A diagnosis of dementia requires more than poor memory or a low test score. I also need to establish whether cognitive change is affecting independence and everyday activities. Structured questionnaires completed by relatives, such as the IQCODE or the Bristol Activities of Daily Living Scale (BADLS), support this judgement but do not diagnose dementia on their own.

4. Cognitive testing

Cognitive tests examine several areas of thinking, including:

• Memory and learning
• Attention and concentration
• Language and verbal fluency
• Visual and spatial abilities
• Planning and problem-solving
• Orientation to time and place

I use validated tests such as the Addenbrooke’s Cognitive Examination (ACE-III) and the Montreal Cognitive Assessment (MoCA). Scores are influenced by education, first language, cultural background, anxiety, depression, hearing or visual impairment, fatigue and other medical problems, so I interpret them clinically rather than as a pass-or-fail result.

5. Physical and neurological examination

Examination can reveal signs that point towards a particular cause of cognitive impairment. Depending on the presentation, I assess:

• Walking and balance
• Muscle strength and coordination
• Tremor, stiffness or slowness of movement
• Eye movements
• Speech and language
• Vision and hearing
• Blood pressure, heart rhythm and cardiovascular health

I also assess mood and look specifically for depression, anxiety, delirium and other psychological symptoms.

6. Medication review

Some medicines worsen memory, alertness or concentration. I pay particular attention to sedatives, sleeping tablets, strong painkillers, medicines with anticholinergic effects (including some bladder, allergy and older antidepressant medicines) and combinations that add to the overall burden. Medicines should not be stopped without first discussing it with the prescriber.

7. Blood tests

Routine blood tests do not diagnose dementia directly. They identify other conditions that can cause or worsen cognitive symptoms. These usually include:

• Full blood count
• Kidney and liver function
• Calcium
• Blood glucose or HbA1c
• Thyroid function
• Vitamin B12 and folate

I add further tests when the history or examination points to a specific cause.

8. CT or MRI brain scan

Structural brain imaging helps identify:

• Previous strokes or small-vessel (vascular) disease
• Brain tumours
• Hydrocephalus
• Previous head injury or subdural haematoma
• Patterns of brain shrinkage that support a particular type of dementia

MRI gives more detailed structural information; CT is used when MRI is unsuitable or unavailable. A scan must always be read alongside the clinical assessment. It cannot diagnose dementia in isolation, and an apparently normal scan does not exclude early dementia. NICE specifically advises against ruling out Alzheimer’s disease on the basis of a CT or MRI scan alone.

Is it dementia, mild cognitive impairment or something else?

Part of every assessment is deciding where a person sits on the spectrum between normal ageing and dementia.

• Mild cognitive impairment (MCI): measurable decline in memory or thinking, but everyday independence is preserved. Some people with MCI go on to develop dementia; many remain stable, and some improve.
• Dementia: cognitive decline that is affecting everyday life and independence.
• Delirium: an acute, fluctuating confusion, usually triggered by infection, medicines, dehydration or another illness. It needs urgent medical attention and must be treated before dementia can be judged.
• Depression and anxiety: can impair concentration and memory, and can also coexist with early dementia.
• Other contributors: medicines, sleep disorders, alcohol, hearing or visual loss, thyroid disease and vitamin deficiency.

Where the picture is not yet clear, a repeat assessment after an interval is often more informative than further tests.

Identifying the type of dementia

The type of dementia matters because it guides treatment, safety advice and what to expect. The clinical pattern is usually the best guide:

Type	Features that point towards it
Alzheimer’s disease	Gradual decline, early difficulty retaining new information, repetition, later word-finding and navigation problems
Vascular dementia	Stroke or vascular risk factors, stepwise or slowed thinking, vascular change on the scan
Mixed dementia	Features of both Alzheimer’s disease and vascular disease; common in older adults
Dementia with Lewy bodies	Fluctuating alertness, visual hallucinations, parkinsonism, acting out dreams during sleep
Parkinson’s disease dementia	Cognitive decline developing in someone with established Parkinson’s disease
Frontotemporal dementia	Earlier onset, change in personality, behaviour or language, with memory relatively preserved at first

Because I also assess TIA and stroke and Parkinson’s disease, vascular and Lewy body features are part of the same assessment rather than a separate referral.

When are specialist tests considered?

Most people do not need advanced scans, a lumbar puncture or biomarker testing. NICE guideline NG97 recommends considering further investigations when:

• The diagnosis remains uncertain after the standard assessment
• Clarifying the type of dementia would be clinically useful
• The result is likely to change treatment or management

The decision should be individual, not driven by the fact that a test exists.

FDG-PET or perfusion SPECT

These scans show patterns of brain activity or blood flow. They can help when Alzheimer’s disease or frontotemporal dementia is suspected but the diagnosis remains uncertain. They are not first-line tests and availability is limited.

Dopamine transporter (DaTSCAN) imaging

A DaTSCAN (123I-FP-CIT SPECT) can support a diagnosis of dementia with Lewy bodies when the clinical picture is uncertain. Where it is unavailable, cardiac MIBG scintigraphy is an alternative. Neither result can be interpreted without the symptoms and examination findings.

Amyloid PET

Amyloid PET detects amyloid deposits in the brain. A negative scan makes Alzheimer’s disease less likely, but a positive scan does not prove that Alzheimer’s disease is causing a person’s symptoms: amyloid is present in some older people who do not have dementia. Amyloid PET is expensive, has limited availability and is not needed for most assessments.

Cerebrospinal fluid (lumbar puncture) biomarkers

Cerebrospinal fluid obtained by lumbar puncture can be analysed for amyloid and tau proteins associated with Alzheimer’s disease. This can help in selected cases where the diagnosis remains uncertain. However:

• It is an invasive procedure
• Results need specialist interpretation
• Abnormal biomarkers do not replace a clinical diagnosis
• Availability varies between services
• It is not needed for most patients

Can a blood test diagnose Alzheimer’s disease?

Not on its own, at present. Blood biomarker tests, particularly those measuring phosphorylated tau (p-tau217), are developing rapidly and are likely to become an important part of assessment. In the UK they are not yet part of routine NHS care; national studies such as the ADAPT trial are evaluating how they should be used, with the aim of bringing them into the NHS by 2029.

A blood biomarker result cannot show by itself:

• Whether cognitive symptoms are affecting everyday independence
• Whether another medical or psychological condition is contributing
• Whether the person has a different type of dementia
• Whether someone with an abnormal result will go on to develop dementia

These tests should not be used to screen people without symptoms. Where I consider one, it forms part of a full clinical assessment, and I explain in advance what the result can and cannot tell us.

Tests that are not used to diagnose dementia

• APOE gene testing: APOE e4 increases the risk of Alzheimer’s disease but does not diagnose it. NICE advises against using it for diagnosis.
• EEG (brain-wave recording): not used to diagnose Alzheimer’s disease, although it has a role when seizures or certain rare conditions are suspected.
• Online memory tests and apps: may prompt someone to seek advice, but cannot diagnose or exclude dementia.

New Alzheimer’s treatments and why biomarkers matter

Lecanemab and donanemab are licensed in the UK for early Alzheimer’s disease. They are only suitable for people whose Alzheimer’s pathology has been confirmed by amyloid PET or cerebrospinal fluid testing, who meet strict eligibility criteria, and who can undergo regular infusions and MRI safety monitoring. NICE has not recommended them for NHS use because the benefits are too small to justify the cost, so they are currently available only privately. Private treatment, including infusions and MRI monitoring, costs around £60,000 to £80,000 a year. If you are interested in these treatments, I will discuss whether you are likely to be eligible, whether confirmatory testing is appropriate, and the realistic benefits, risks and costs.

Availability and cost of advanced tests

Access to specialist biomarker testing remains variable. Some investigations are available only through specialist NHS cognitive or neurology services, selected memory services, university research centres, clinical trials or a small number of private providers.

Private PET imaging, specialist laboratory analysis, lumbar puncture and the associated consultations are expensive, and combined investigations can cost several thousand pounds. A more expensive test does not automatically give a more reliable diagnosis. Before any advanced test, you should understand:

• What clinical question the test is intended to answer
• Whether the result is likely to change treatment
• The limitations of the test
• The possibility of an uncertain or misleading result
• Any risks or discomfort
• The total likely cost
• Whether an NHS or research pathway may be more appropriate

How I carry out a memory assessment in Sheffield

1. Before the appointment: you and a relative complete my pre-consultation assessment, so the consultation time is spent on what matters.
2. Consultation: history, informant account, cognitive testing, examination, mood assessment and a full medication review, within a Comprehensive Geriatric Assessment.
3. Investigations: I review existing blood tests and scans, and arrange any that are needed at a private hospital. Specialist tests are discussed only when there is a clear clinical question.
4. Diagnosis and plan: I explain the diagnosis and how certain it is, discuss treatment, and send a detailed written report to you and your GP.
5. Follow-up: where treatment is started, I arrange review to monitor benefit, side effects and how carers are coping.

I see patients at Spire Claremont Hospital and Circle Thornbury Hospital in Sheffield, at LivingCare, Sheffield, at home across Sheffield and surrounding areas, and by video consultation. Appointments are usually available within 24 to 48 hours, and no GP referral is required. A new-patient memory assessment is £800 in clinic at Spire Claremont or Circle Thornbury (60 minutes) and £900 at home (60 minutes). Full details are on my fees page.

Private or NHS memory assessment?

NHS memory services, including Sheffield Memory Service, provide specialist assessment free at the point of care, usually following referral from a GP. Waiting times can be several months. A private assessment offers faster access, a longer consultation with a consultant, and a whole-person assessment covering physical health and medicines alongside memory. Either route follows the same NICE principles. For a fuller comparison, see my guide to private memory assessment in Sheffield.

Frequently asked questions

Can dementia be diagnosed from a blood test?

Not from a blood test alone at present. Routine blood tests identify other causes of cognitive symptoms. Newer Alzheimer’s blood biomarker tests, such as p-tau217, are promising but are not yet part of routine NHS care, and they still need specialist interpretation alongside the history, cognitive assessment and other investigations.

Does an MRI scan confirm dementia?

No. MRI can show vascular changes, structural abnormalities and patterns of shrinkage that support a particular diagnosis, but it cannot confirm or exclude dementia by itself.

Can someone have dementia with a normal brain scan?

Yes. Structural changes can be subtle in the early stages, which is why a scan is always interpreted alongside the person’s symptoms and any change in everyday function.

Can a cognitive test diagnose dementia?

No. Cognitive tests such as the ACE-III or MoCA measure different thinking abilities, but scores are affected by education, language, anxiety, fatigue, hearing, vision and other medical conditions. A score is one piece of evidence, not a diagnosis.

Does poor memory always mean dementia?

No. Memory and concentration can be affected by anxiety, depression, poor sleep, medicines, pain, alcohol, hearing or visual loss, thyroid disease, vitamin deficiency and other medical conditions. Identifying these is a core part of my assessment.

What is the difference between mild cognitive impairment and dementia?

In mild cognitive impairment, memory or thinking has declined measurably but everyday independence is preserved. In dementia, the decline is affecting daily life. Some people with mild cognitive impairment develop dementia, while others remain stable or improve.

Does everyone need a PET scan or lumbar puncture?

No. Most people can be assessed with a clinical history, examination, cognitive testing, blood tests and structural brain imaging. Advanced tests are considered when uncertainty remains and the result is likely to change management.

Should people without symptoms have an Alzheimer’s biomarker or APOE gene test?

Routine biomarker or genetic screening of people without symptoms is not recommended. A positive biomarker does not mean that a person has dementia or will inevitably develop it, and APOE testing indicates risk only.

How long does it take to get a dementia diagnosis?

On the NHS, waiting times for a memory service can be several months. Privately, I can usually see patients within 24 to 48 hours. In many cases a diagnosis can be given at or shortly after the consultation once blood tests and imaging are reviewed; where the picture is uncertain, a planned reassessment is safer than an early label.

Do I need a GP referral for a private memory assessment?

No. You or a relative can contact me directly. With your consent, I send a detailed report to your GP after the assessment.

Can a memory assessment be done at home?

Yes. I carry out home assessments across Sheffield and surrounding areas, which can suit people who find hospital visits difficult. The history, informant account, cognitive testing, examination and medication review can all be completed at home, and any blood tests or scans are then arranged at a private hospital.

What should I bring to a memory assessment?

An up-to-date list of medicines, relevant medical letters, any previous cognitive test results and details of brain scans. If possible, attend with someone who knows you well and can describe the changes they have noticed.

Arrange a memory assessment

If you or a relative has noticed a change in memory, thinking, behaviour or everyday functioning, a consultant assessment can clarify the likely causes and whether further investigation is needed. No GP referral is required.

Book at Spire Claremont · 0114 263 0330Book at Circle Thornbury · 0114 266 1133Book at LivingCareRequest a home visit

About my private memory assessment · View consultation fees

---

Clinical review

Written and clinically reviewed by Dr Pravin Jha, Consultant Geriatrician and Stroke Physician. MBBS, MD, DIM, PgDGM, MRCP (UK), FRCP (Edin.). GMC 4755744.

Last reviewed: September 2026. Next planned review: September 2027.

This information is educational and does not replace an individual medical assessment.

References

1. National Institute for Health and Care Excellence. Dementia: assessment, management and support for people living with dementia and their carers (NG97), 2018. https://www.nice.org.uk/guidance/ng97
2. NHS. Tests for diagnosing dementia. https://www.nhs.uk/conditions/dementia/symptoms-and-diagnosis/tests/
3. Alzheimer’s Research UK. NHS patients denied new Alzheimer’s drugs, June 2025. https://www.alzheimersresearchuk.org/news/nhs-patients-denied-new-alzheimers-drugs/
4. Alzheimer’s Research UK. UK trial launches to transform Alzheimer’s diagnosis with simple blood test (ADAPT), 2025. https://www.alzheimersresearchuk.org/news/uk-trial-launches-to-transform-alzheimers-diagnosis-with-simple-blood-test/