When individuals notice changes in memory, thinking, language, or behavior, an essential question surfaces: what is causing these changes? Many brain conditions can appear similar, particularly in their early stages. Biomarkers enable doctors to look beyond symptoms and gain an understanding of what is occurring biologically within the brain.

This guide explains what biomarkers are, how they are measured, and their role in diagnosing, monitoring, and planning care for cognitive and neurodegenerative conditions.

What Are Biomarkers?

A biomarker is a measurable biological signal that provides insight into internal body processes. For brain health, biomarkers can indicate changes in brain proteins, nerve cells, blood vessels, or supporting cells.

Consider biomarkers as biological clues. While they don't replace a clinical evaluation, they can help explain why symptoms may be occurring and whether a specific brain disease is present.

Why Biomarkers Are Important

Symptoms such as forgetfulness, confusion, slowed thinking, or language difficulties can have various causes. Biomarkers assist clinicians in:

• Identifying the underlying cause of cognitive changes
• Detecting disease-related changes before symptoms become severe
• Guiding treatment decisions and monitoring
• Reducing uncertainty for patients and families

Biomarkers serve as tools for understanding, rather than predictions or guarantees.

Core Brain Proteins Measured by Biomarkers

Amyloid

Amyloid is a protein that can accumulate in the brain over many years, indicating Alzheimer's disease. Changes in amyloid often begin long before memory symptoms appear, making amyloid biomarkers useful even in early stages.

Tau

Tau is involved in maintaining brain cell structure. In diseases like Alzheimer's, tau becomes abnormally modified and spreads through brain networks. Tau levels often more closely reflect disease activity and progression than amyloid.

Alpha-synuclein

Alpha-synuclein is associated with conditions such as Parkinson's disease, dementia with Lewy bodies, and multiple system atrophy. Abnormal alpha-synuclein affects both the brain and peripheral nerves.

Markers of Nerve Injury and Stress

Some biomarkers indicate nerve cell injury, inflammation, or stress in the brain, rather than a specific disease. These help clinicians understand if active damage is occurring and how the brain is responding.

How Biomarkers Are Measured

Biomarkers can be measured using various methods, each offering different insights. Not every individual requires every test.

Blood Biomarkers

Blood tests are increasingly used as a first step in cognitive evaluation. Blood biomarkers can:

• Screen for Alzheimer-related protein changes
• Estimate the likelihood that amyloid or tau is present in the brain
• Help determine whether further testing is needed

Blood tests are minimally invasive and widely accessible, typically serving as screening tools, not definitive answers.

Cerebrospinal Fluid (CSF) Biomarkers

CSF, which surrounds the brain and spinal cord, closely reflects brain biology. It is collected through a lumbar puncture (sometimes called a spinal tap). CSF biomarkers can:

• Measure amyloid and tau with high accuracy
• Help confirm or rule out Alzheimer's disease
• Identify conditions that can mimic neurodegenerative disease

Although more invasive than blood tests, CSF testing often provides greater diagnostic clarity, especially in complex or atypical cases.

Brain Imaging Biomarkers

MRI (Magnetic Resonance Imaging)

MRI doesn't measure specific proteins but provides crucial information about brain structure and health, including:

• Patterns of brain shrinkage (atrophy)
• White matter and small vessel disease
• Prior strokes or silent injuries
• Microbleeds or blood vessel fragility

MRI is vital for understanding the brain's overall condition and assessing safety when considering certain treatments.

CT Scan

CT scans quickly identify major structural problems like bleeding, masses, or hydrocephalus. They are less sensitive than MRI for subtle neurodegenerative changes but useful in certain settings.

PET Imaging

PET scans allow doctors to observe specific biological activity in the brain:

• Amyloid PET shows whether amyloid plaques are present
• Tau PET shows where abnormal tau has accumulated
• FDG-PET shows brain network activity by measuring glucose metabolism

PET scans are typically used when results will meaningfully change diagnosis or management.

Skin and Peripheral Nerve Biomarkers

Some brain diseases affect nerves outside the brain. In such cases, biomarkers can be detected in the skin. A skin biopsy can detect abnormal alpha-synuclein in small nerve fibers. This test is:

• Minimally invasive
• Does not involve the brain or spinal cord
• Can support diagnosis of certain movement and cognitive disorders

Results are always interpreted alongside symptoms and other tests.

What Biomarkers Can and Cannot Tell Us

Biomarkers can:

• Identify disease-related biology
• Support or clarify diagnoses
• Help guide treatment decisions
• Assist with monitoring over time

Biomarkers cannot:

• Predict exact timelines
• Determine how fast someone will change
• Replace clinical evaluation and daily function assessment
• Capture resilience, support, or quality of life

A positive biomarker does not indicate rapid decline. A negative biomarker does not mean no follow-up is needed.

Biomarkers and Early Detection

One of the key roles of biomarkers is identifying changes early, when symptoms are mild or even absent. Early understanding allows for:

• Optimization of sleep, mood, and medical factors
• Careful monitoring over time
• Consideration of disease-modifying therapies when appropriate
• Thoughtful planning and education

Early knowledge is about options and preparation, not alarm.

How Biomarkers Fit Into Care

Biomarker results are part of an ongoing conversation. They are revisited as symptoms, function, and goals change. Decisions are made collaboratively, based on:

• Clinical findings
• Daily functioning
• Personal values and priorities
• Risks and benefits of testing or treatment

There is rarely a single "right" path. The goal is understanding and informed choice.

What This Means for Patients and Families

Biomarkers help shift cognitive care from uncertainty to clarity. They allow clinicians to explain symptoms based on brain biology rather than labels alone. Used thoughtfully, biomarkers support better understanding, safer decisions, and more personalized care.

If biomarker testing is recommended, it is not to define your future - it is to better understand your brain health today and guide next steps with confidence and care.