What tests are used to confirm Alzheimers dementia? 

Confirming a diagnosis of Alzheimers disease is a multi stage process that combines clinical observation with objective medical testing. Because there is no single test that can definitively prove a person has Alzheimers during their lifetime, healthcare professionals use a series of investigations to build a comprehensive picture of brain health. These tests are designed not only to identify cognitive decline but also to rule out other treatable medical conditions that can cause similar symptoms, such as vitamin deficiencies, infections, or thyroid problems. 

The diagnostic pathway involves a transition from primary care, usually with a General Practitioner, to specialist services such as memory clinics. At each stage, specific tools are used to measure different aspects of brain function, structure, and chemistry. From simple pen and paper tests to advanced neuroimaging, each investigation provides a piece of the puzzle. By the end of the process, clinicians can determine the likelihood of Alzheimers with a high degree of accuracy, allowing for early intervention and support planning. 

What we will discuss in this article 

• The role of clinical history and physical examinations in the initial assessment 

• Common cognitive screening tools like the GPCOG and ACE III 

• Blood tests used to rule out reversible causes of memory loss 

• Structural brain imaging techniques including MRI and CT scans 

• Functional brain scans such as SPECT and PET for complex cases 

• The emerging role of cerebrospinal fluid analysis and biomarkers 

• Emergency guidance for identifying signs of health deterioration 

Initial clinical assessment and history 

The first step in confirming Alzheimers is a detailed clinical consultation, often starting at the GP surgery. This assessment focuses on the pattern of symptoms and how they have changed over time. 

Taking a detailed history 

The clinician will ask the individual and a close family member or friend about the onset of memory problems. They will look for hallmark signs of Alzheimers, such as difficulty learning new information, repetitive questioning, or getting lost in familiar places. A witness account is vital because individuals with the condition may not always be aware of the extent of their difficulties. The doctor will also review current medications and existing health conditions like hypertension or diabetes, which can impact cognitive health. 

Cognitive screening tools and mental ability tests 

To objectively measure cognitive function, healthcare professionals use standardised tests that assess memory, language, and reasoning. 

Common screening assessments 

In primary care, short tests like the General Practitioner Assessment of Cognition or the 6 Item Cognitive Impairment Test are often used. If a referral to a memory clinic is made, more detailed assessments like the Addenbrooke Cognitive Examination or the Montreal Cognitive Assessment are utilised. These tests involve tasks such as recalling a name and address, identifying the current date, naming common objects, and drawing a clock face. These tools help clinicians determine which specific areas of the brain are being affected by the disease. 

Laboratory investigations and blood tests 

A core part of the diagnostic process is performing blood and urine tests to ensure the cognitive symptoms are not caused by an underlying physical illness. 

Ruling out other conditions 

The GP will arrange for a suite of blood tests to check for issues that can mimic dementia. These typically include: 

• Thyroid function tests to check for an underactive thyroid 

• Vitamin B12 and folate levels to identify deficiencies 

• Kidney and liver function tests 

• HbA1c levels to screen for diabetes 

• Full blood count and inflammatory markers to check for infections 

If these tests are normal, it strengthens the clinical suspicion that a neurodegenerative condition like Alzheimers is the cause of the symptoms. 

Advanced brain imaging techniques 

Brain scans are used to look at the physical structure and function of the brain, helping to confirm the type of dementia and rule out other problems. 

Structural imaging: MRI and CT 

Magnetic Resonance Imaging is the preferred structural scan for Alzheimers. It provides detailed images that show if specific areas of the brain, such as the hippocampus, are shrinking. This shrinking, known as atrophy, is a key marker of Alzheimers. Computed Tomography scans may be used if an MRI is not possible, primarily to look for signs of a stroke, brain tumour, or a buildup of fluid in the brain. 

Functional imaging: SPECT and PET 

In cases where the diagnosis is still unclear after an MRI, functional scans may be requested. A SPECT scan measures blood flow in the brain, while a PET scan can identify how the brain uses glucose or detect the presence of amyloid plaques. These scans show the brain in action and can reveal abnormalities in brain activity even before significant structural shrinkage is visible. 

Emerging diagnostic biomarkers and fluid analysis 

Research has led to the development of more specialized tests that can detect the biological signs of Alzheimers directly from body fluids. 

Cerebrospinal fluid analysis 

A lumbar puncture can be performed to collect a sample of cerebrospinal fluid, the liquid that surrounds the brain and spinal cord. Specialists can then measure the levels of specific proteins: amyloid and tau, that are known to build up in the brains of people with Alzheimers. Abnormal levels of these proteins in the fluid provide strong evidence of the disease. While more invasive than a scan, this test is highly accurate in the early stages of the condition. 

To summarise 

Confirming Alzheimers dementia requires a structured clinical approach that combines history taking, cognitive testing, and medical imaging. By moving through these stages, clinicians can accurately distinguish Alzheimers from other forms of dementia or treatable medical issues. While structural scans like MRI remain a cornerstone of the process, the use of functional imaging and biomarkers is becoming increasingly important for early and precise diagnosis. Receiving a formal confirmation is a vital step in accessing the right clinical care and planning for the future. 

Emergency guidance 

While Alzheimers is a slow, progressive disease, sudden changes in mental state are not typical and require urgent attention. Call 999 or seek immediate clinical help if a person experiences a sudden onset of severe confusion, known as delirium, or shows signs of a stroke, such as facial drooping or slurred speech. Sudden confusion is often caused by treatable factors like a urinary tract infection or a reaction to a new medication. Prompt medical intervention is necessary to identify these causes and prevent further deterioration or injury to the brain. 

Authority Snapshot 

Dr. Rebecca Fernandez is a physician with an MBBS and experience in general surgery, cardiology, internal medicine, gynecology, intensive care, and emergency medicine. She has managed critically ill patients, stabilised acute trauma cases, and provided comprehensive inpatient and outpatient care. In psychiatry, Dr. Fernandez has worked with psychotic, mood, anxiety, and substance use disorders, applying evidence based approaches such as CBT, ACT, and mindfulness based therapies. Her skills span patient assessment, treatment planning, and the integration of digital health solutions to support mental well being in 2026.