A PCP’s Guide to Blood-Based Alzheimer’s Testing

Blood-based Alzheimer’s testing has progressed from a research discussion to a practical, clinic-ready implementation.

For primary care physicians, these assays provide a more straightforward pathway for early detection, risk clarification, and more informed conversations about memory health.

This guide brings the science down to the point of care, outlining what today’s blood-based biomarkers mean, when testing influences management, and how to incorporate results into a prevention-first clinical approach.

What PCPs Need to Know About Blood-Based Alzheimer’s Testing

Blood-based biomarkers detect molecular changes associated with Alzheimer’s pathology, including amyloid deposition, tau phosphorylation, and neurodegeneration.

These assays don’t diagnose Alzheimer’s alone, but they meaningfully contribute to earlier detection and clinical decision-making.

In primary care, their value lies in improving triage. Biomarker results help determine whether patients need further imaging, specialist referral, or closer longitudinal monitoring.

Key Alzheimer’s Plasma Biomarkers Every PCP Should Be Aware Of

Multiple biomarkers can help physicians better understand most blood-based Alzheimer’s evaluations. Each offers unique insight into whether Alzheimer’s-type changes may be present.

P-tau217

Plasma p-tau217 is one of the most reliable blood biomarkers available.

Research consistently demonstrates strong alignment with amyloid PET results and clear differentiation between Alzheimer’s and other neurodegenerative conditions.

In practice, p-tau217 is valuable because it:

• Shows high specificity for Alzheimer’s pathology
• Often becomes abnormal early, before structural changes on MRI
• Strengthens confidence when other markers point in a similar direction

When p-tau217 is abnormal in a patient with compatible symptoms, the likelihood of Alzheimer’s-type processes increases significantly.

P-tau181

P-tau181 also reflects tau phosphorylation, though with slightly less specificity. Still, it remains meaningful, especially when used in conjunction with p-tau217.

Screening for p-tau181 is beneficial when:

• p-tau217 is unavailable
• You’re looking for a pattern across multiple tau markers
• You’re assessing whether tau-related changes are consistent over time

Aβ42/40 Ratio

The Aβ42/40 ratio offers insight into amyloid burden. Lower ratios often indicate greater amyloid deposition, providing important context to tau findings.

When tau markers are abnormal, a concordant drop in Aβ42/40 reinforces the pattern.

Because amyloid changes often occur years before symptoms, shifts in the Aβ42/40 ratio can help clarify whether tau abnormalities are happening in an amyloid-positive context.

How Blood Tests Compare to CSF and Imaging

Blood-based tests don’t replace CSF or imaging, but they can make those tools more targeted and accelerate time to treatment by up to 4.5 years.

• Compared with CSF, blood tests are far less invasive, easier to repeat, and increasingly concordant with CSF markers — especially for p-tau217 and amyloid-related measures.
• Compared with MRI, biomarkers often become abnormal before structural atrophy appears, offering a chance to act earlier, while MRI remains normal or nonspecific.
• Compared with PET, blood tests can flag patients who are most likely to benefit from PET confirmation, which is still costly and not universally available or covered.

From a workflow perspective, blood tests function as a front-line filter. They help you decide who truly needs advanced imaging and who can be safely managed with monitoring and prevention-focused care in primary care.

When PCPs Should Order Blood-Based Alzheimer’s Testing

Identifying the right moment to use biomarkers is key. It helps to think about testing in terms of its purpose: clarifying risk early and guiding next steps before symptoms become advanced.

Appropriate Use Cases

Blood-based testing tends to be most helpful in patients who:

• Have subtle or early memory concerns
• Present with a family history or elevated risk factors
• Show functional changes reported by a spouse or child

These situations often create clinical uncertainty, and biomarkers help you move from “wait and see” to “here’s what we should consider next.”

Red Flags Requiring Faster Workup

There are also cases where biomarker testing can support more urgent escalation:

• Rapid cognitive decline
• Atypical presentations (language, visuospatial, or behavioral changes)
• Onset before age 65
• Complex psychiatric or vascular comorbidities

In these circumstances, positive or elevated biomarkers support the case for expedited imaging or referral, while normal biomarker results don’t remove the need for further workup.

Communicating Biomarker Results With Patients

It's important to remember the emotional landscape when discussing Alzheimer's Disease with patients. They often arrive with fear, uncertainty, or long-standing questions.

Your framing guides their next steps and helps them understand what their results truly mean.

How to Frame Positive Findings

Positive results can be challenging, but they also offer clarity that patients often appreciate. Helpful ways to approach the conversation include:

• The results help explain what you’ve been noticing together
• Early awareness creates more options for planning and support
• There are actionable steps — medical, preventive, and lifestyle-based — that can improve outcomes

How to Discuss Negative Results

Negative biomarkers offer reassurance, particularly for patients with mild or nonspecific symptoms. You can reinforce that:

• Current results look stable
• Ongoing prevention still matters
• You’ll continue monitoring over time

This approach strikes a balance between reassurance and responsible long-term care.

Managing Uncertainty

Elevated or borderline findings often cause the most concern as patients seek certainty. You can reduce confusion by:

• Being clear about what’s known and what’s not yet known
• Setting expectations for follow-up or repeat testing
• Explaining situations where imaging might add clarity

These conversations help patients stay grounded and engaged, regardless of result category.

Integrating Blood-Based Alzheimer’s Testing Into Primary Care Workflow

Memory health becomes more manageable when biomarker testing is integrated into a defined workflow, rather than an ad-hoc decision.

Practical ways to integrate testing include:

• Incorporating memory health conversations into annual wellness visits
• Using biomarkers when cognitive testing is inconclusive
• Documenting baseline biomarker results for future comparison
• Setting precise follow-up intervals based on the result category
• Tracking functional changes alongside biomarker trends

This approach transforms memory health into an ongoing, proactive component of primary care, rather than a late-stage crisis intervention.

How Neurogen’s Ecosystem Supports PCPs

Neurogen’s prevention-first ecosystem provides science-based biomarker testing paired with accessible patient education.

It’s designed to support both clinicians and patients through transparent reporting and easy-to-understand explanations.

By combining research-backed assays with practical communication tools, Neurogen helps primary care teams bring memory health to the forefront — without adding complexity to already busy workflows.