Alzheimer’s Blood Test: p-tau217, Aβ42/40 & Biomarkers for Faster Diagnosis

Alzheimer’s Blood Tests: Faster, Less Invasive Diagnosis

For the first time, blood-based biomarkers are officially recognized as a valid tool to support the diagnosis of Alzheimer’s Disease and strengthen cognitive health. On July 29, 2025, the Alzheimer’s Association released its first Clinical Practice Guideline on biomarkers like p-tau217, p-tau181, the Aβ42/40 ratio, APOE genotype, Neurofilament Light Chain (NfL), and Glial Fibrillary Acidic Protein (GFAP). These tests help clarify causes of memory loss and track the progression from Mild Cognitive Impairment (MCI) to cognitive decline.

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Why This Guideline Matters

This milestone, highlighted in the Alzheimer’s Association blood test guideline, shifts the field of neurology toward less invasive and more affordable options. For patients and caregivers searching for a blood test for Alzheimer’s accuracy, wanting to understand the p-tau217 blood test meaning, or considering APOE testing for Alzheimer’s, these innovations provide clear answers. They also respond to common questions like “how to diagnose Alzheimer’s without spinal tap” and whether blood tests vs PET for Alzheimer’s are the better option.

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FDA Clearance: A Breakthrough Step

On May 16, 2025, the FDA cleared the first Alzheimer’s blood test—a plasma assay reporting the p-tau217/β-amyloid 1-42 ratio. While not a general population screening tool, it represents a meaningful step forward in delivering a less invasive Alzheimer’s diagnosis.

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A New Era in Alzheimer’s Diagnostics

As Heather Snyder, PhD, of the Alzheimer’s Association explained, this development marks a new era in Alzheimer’s diagnostics, improving access and reducing reliance on PET scans and spinal taps. With providers like Ulta Lab Tests offering affordable Alzheimer’s testing online, patients and families can now search for an Alzheimer’s blood test near me, order from the best labs for cognitive decline, and use rule-out labs for memory loss to take action sooner and protect long-term brain health & prevention.

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A Major Milestone in Alzheimer’s Diagnosis

• What changed: The Alzheimer’s Association now supports specialty‑care use of specific blood‑based biomarkers—notably p‑tau217 and the Aβ42/40 ratio—to help assess the presence of Alzheimer’s pathology in people with cognitive symptoms. 
• Why it matters: The FDA’s May 2025 clearance validates the role of plasma testing to aid diagnosis in appropriate patients. It can reduce the need for invasive lumbar punctures and costly PET scans, streamlining care and improving access.

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Signs & Symptoms: When to Consider Testing

If you or a loved one has new or worsening cognitive concerns, talk with your clinician about evaluation and Alzheimer’s blood tests:

• Memory loss (misplacing items, repeating questions)
• Word‑finding difficulty, losing the thread in conversations
• Trouble with planning/organization (bills, recipes, medications)
• Confusion about time/place or getting lost on familiar routes
• Personality or mood changes (apathy, anxiety, depression)
• Declining work, school, or household performance

Important: Many reversible issues can mimic dementia—thyroid disorders, vitamin B12 or folate deficiency, depression, sleep apnea, medication effects, infection. Including rule‑out labs for memory loss is essential in any thorough workup (see below).

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Why Blood‑Based Testing Is Transformative

Traditional diagnosis has relied on clinical testing plus amyloid or tau PET scans or CSF analysis. While effective, those methods are invasive, expensive, and not always available. Blood‑based biomarkers offer a practical first step that can:

• Detect underlying pathology earlier in the course of disease
• Reduce barriers for underserved and rural communities
• Help primary care teams triage patients efficiently
• Streamline referrals to specialists or clinical trials
• Provide a less invasive path for people asking, “How can we diagnose Alzheimer’s without a spinal tap?”

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What These Alzheimer’s Blood Tests Measure

Core Alzheimer’s biomarkers (blood‑based):

• Amyloid Beta (Aβ42/40 ratio): Lower ratios suggest amyloid plaque deposition. Often paired with p‑tau markers to improve blood test for Alzheimer’s accuracy.
• Phosphorylated Tau (p‑tau181 and p‑tau217): Elevated levels reflect tau tangle biology, strongly associated with Alzheimer’s pathology and disease stage. p‑tau217 generally shows the strongest performance in head‑to‑head studies.

Supportive biomarkers of neurodegeneration and astroglial injury:

• Neurofilament Light Chain (NfL): Marker of axonal injury; levels tend to rise with neurodegeneration and can help track disease activity and severity. Not specific to Alzheimer’s. 
• Glial Fibrillary Acidic Protein (GFAP): Marker of astrocytic activation and neuroinflammation; elevated in amyloid‑positive individuals and helps distinguish etiologies in research/clinical settings.

Kidney function matters: Emerging evidence shows reduced eGFR/CKD can elevate plasma p‑tau217values. Some algorithms use ratios that are less affected. Clinicians may review renal function alongside results. 

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How Lab Tests Help Diagnose and Manage Alzheimer’s

1. Aid diagnosis, earlier and more accessibly
   Combining p‑tau217 with Aβ42/40 improves agreement with PET/CSF and helps determine who needs confirmatory testing—especially in specialty settings.
2. Guide treatment conversations
   Some disease‑modifying therapies (e.g., anti‑amyloid monoclonal antibodies) require evidence of amyloid pathology. Blood‑based biomarkers can be a first step to confirm eligibility and plan ARIA‑risk counseling (often informed by APOE status).
3. Support whole‑person brain health
   Additional labs—thyroid (TSH), B12/folate, vitamin D, lipids, A1c, inflammation markers—help detect treatable contributors to cognitive decline.

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The Alzheimer’s Association’s Updated Recommendations (Plain‑Language Summary)

• Use blood tests as part of a stepwise diagnostic approach—particularly in specialty care—and confirm with PET or CSF when results are positive/indeterminate or the case is complex.
• Interpret BBMs with clinical context (history, cognitive testing, exam).
• Do not use BBMs as a stand‑alone diagnosis tool, especially in atypical presentations.
• Blood tests can be most helpful in suspected MCI due to Alzheimer’s, when early treatment discussions may be most impactful.

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Individual Test Breakdowns (with direct ordering links)

Results should be interpreted by a qualified clinician. Blood tests aid diagnosis; they do not replace clinical evaluation.

p‑tau217 (Plasma)

• What it is: Blood test for phosphorylated tau 217—a tau species with strong diagnostic performance.
• What it measures: p‑tau217 linked to amyloid‑driven tau pathology.
• Why it matters: Among plasma biomarkers, p‑tau217 often shows highest accuracy for Alzheimer’s pathology and staging.
• How it helps: Can reduce invasive tests and prioritize confirmatory steps.
• Order: Quest AD‑Detect™ p‑tau217, Plasma 

Amyloid Beta 42/40 Ratio (Plasma)

• What it is: The Aβ42/40 ratio; lower values suggest amyloid plaque presence.
• Why it matters: Combining the amyloid beta 42/40 ratio test with p‑tau217 increases diagnostic confidence.
• Order: Quest AD‑Detect™ Aβ42/40 Ratio, Plasma 

p‑tau181 (Plasma)

• What it is: Blood test for phosphorylated tau 181.
• Why it matters: Another Alzheimer’s‑related tau signal; may be used when p‑tau217 is unavailable or as complementary data.
• Order: Quest AD‑Detect™ p‑tau181, Plasma

APOE Testing (Isoform / Genotype)

• What it is: APOE influences lipid transport; ε4 increases risk and is associated with ARIA risk discussions for some therapies.
• Purpose: Not diagnostic, but supports risk counseling and treatment planning.
• Order: AD‑Detect™ APOE Isoform, Plasma 
  Cardio IQ™ APOE Genotype
  ADmark® APOE Genotype Analysis

NfL and GFAP (Supportive Markers)

• Neurofilament Light (NfL): Marker of axonal injury; helpful for monitoring neurodegeneration but not Alzheimer’s‑specific. Availability may vary; check our Alzheimer’s category. 
• Glial Fibrillary Acidic Protein (GFAP): Marker of astrocyte activation; often elevated in amyloid‑positiveindividuals and can help differentiate dementia causes. Availability may vary; check our Alzheimer’s category.

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What to Expect From Your Results

• Report style: Many labs report positive / negative / indeterminate relative to validated cutoffs.
• Positive (or high‑probability) results: Increase the likelihood that symptoms are due to Alzheimer’s pathology; your clinician may order PET or CSF for confirmation, per the Alzheimer’s Association blood test guideline.
• Negative results: Make Alzheimer’s pathology less likely; clinicians often pursue other causes or monitor over time.
• Indeterminate: May reflect early disease, biological variability, or comorbidities (e.g., CKD); your clinician may repeat or confirm with PET/CSF.
• Limitations: No blood test is perfect; false positives/negatives occur. The FDA‑cleared test is for adults ≥55 with symptoms and is not a population screen. 

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Blood Tests vs PET or Spinal Tap: How They Fit Together

• Blood tests (p‑tau217, Aβ42/40) are first‑line in specialty care to triage and inform next steps.
• PET or CSF is often used to confirm positive or uncertain blood results, guide treatment eligibility, or clarify atypical cases.
• This stepwise approach improves access and lowers cost without sacrificing diagnostic rigor.

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Living Well: Strategies to Manage and Maintain a Healthy Life

Whether Alzheimer’s blood tests are positive or negative, these steps support brain health and day‑to‑day function:

1. Treat the treatable (rule‑out labs for memory loss)
   • Thyroid: TSH Test, Thyroid Panel with TSH
   • B‑vitamins: Vitamin B12, Folate, RBC
   • Vitamin D: 25‑OH Vitamin D
   • General health: CBC with Differential — Order your CBC test here.
     Comprehensive Metabolic Panel (CMP)
   • Heart‑brain risk: Lipid Panel with Ratios, Hemoglobin A1c, hs‑CRP, Homocysteine
2. Protect your heart to protect your brain
   Aim for 150 minutes/week of moderate aerobic activity plus strength and balance work; keep BP, LDL, and A1con target.
3. Nutrition (MIND‑style)
   Emphasize leafy greens, berries, legumes, whole grains, fish, nuts; moderate sodium and added sugars.
4. Sleep, hearing, mood
   Treat sleep apnea, use hearing aids if indicated, address depression/anxiety.
5. Stay mentally & socially active
   Cognitive stimulation, purpose, and relationships matter.
6. Discuss treatment options
   If Alzheimer’s biomarkers are positive, ask about disease‑modifying therapies, APOE testing for Alzheimer’srisk counseling, and safety monitoring plans.

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Are These Tests Available to the Public?

Yes. Ulta Lab Tests offers multiple Quest AD‑Detect™ blood tests you can order online with convenient patient service centers near you (think “Alzheimer’s blood test near me”). Other commercial options exist—such as PrecivityAD2™ by C2N (LC‑MS/MS algorithm using %p‑tau217 and Aβ42/40) and platform assays from Quanterix (Simoa®)—mostly accessed through specialty clinics or research settings. Diadem’s AlzoSure® Predict (prognostic U‑p53AZ) is CE‑IVD marked in the EU and has U.S. collaborations; availability varies. Always discuss which test best fits your situation with your clinician.

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Ulta Lab Tests: Alzheimer’s Blood‑Test Portfolio (Quick Reference)

Test (Ulta link)	Purpose	Typical Use Case
AD‑Detect™ Aβ42/40 Ratio, Plasma	Detects amyloid plaque biology	Early triage; blood tests vs PET conversations
AD‑Detect™ p‑tau217, Plasma	Detects tau tangle biology	Confirmation of Alzheimer’s pathology likelihood; eligibility triage
AD‑Detect™ p‑tau181, Plasma	Complementary tau signal	When p‑tau217 is unavailable or as supportive data
AD‑Detect™ APOE Isoform, Plasma	Protein‑based APOE status	APOE testing for Alzheimer’s therapy counseling (e.g., ARIA risk)
Cardio IQ™ APOE Genotype	DNA‑based APOE genotype	Risk counseling; personalized prevention
ADmark® APOE Genotype Analysis	Genotype (symptomatic focus)	Specialty evaluation in symptomatic patients

Additional supportive markers (e.g., NfL, GFAP) may be available in select settings; check our Alzheimer’s category.

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When to Talk to Your Doctor

• New or worsening memory or thinking changes
• A positive or indeterminate Alzheimer’s blood test result
• Before starting medications that may impact cognition
• Considering disease‑modifying therapy or a clinical trial
• Difficulty with sleep, mood, pain, or lifestyle barriers to brain health

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Conclusion / Next Steps

Blood-based biomarkers are ushering in a new era for Alzheimer’s Disease diagnosis and cognitive health, offering faster, less invasive options that expand access and hope.

With advanced tools like the Alzheimer’s blood test measuring p-tau217, p-tau181, and the Aβ42/40 ratio, along with genetic insights from APOE genotype and supportive markers like Neurofilament Light Chain (NfL) and Glial Fibrillary Acidic Protein (GFAP), patients and providers now have powerful resources to evaluate memory loss, mild cognitive impairment (MCI), and ongoing cognitive decline.

The Alzheimer’s Association blood test guideline emphasizes using these tests within a stepwise clinical framework. This guidance helps answer important questions such as the p-tau217 blood test meaning, the role of the amyloid beta 42/40 ratio test, and how best to approach APOE testing for Alzheimer’s risk.

For families searching “how to diagnose Alzheimer’s without spinal tap” or comparing blood tests vs PET for Alzheimer’s, these innovations provide clarity and convenience. Many can now access affordable Alzheimer’s testing online, often through trusted providers like Ulta Lab Tests.

Whether you’re looking for the “Alzheimer’s blood test near me” or exploring the best labs for cognitive decline, today’s advances make it easier than ever to take charge of your health. These tests help patients and caregivers rule out reversible causes and move toward personalized, preventive care—paving the way for better brain health & preventionacross the field of neurology.

Ready to move forward?

• Explore our Alzheimer’s & Cognitive Health tests: https://www.ultalabtests.com/testing/categories/cognitive-health/alzheimers-disease
• Or order key tests directly:
  • p‑tau217 (Plasma): https://www.ultalabtests.com/test/quest-ad-detect-phosphorylated-tau217-p-tau217-plasma
  • Aβ42/40 Ratio (Plasma): https://www.ultalabtests.com/test/quest-ad-detect-beta-amyloid-42-40-ratio-plasma
  • p‑tau181 (Plasma): https://www.ultalabtests.com/test/quest-ad-detect-phosphorylated-tau181-p-tau181
  • APOE Isoform / Genotype: https://www.ultalabtests.com/test/quest-ad-detect-apolipoprotein-e-apoe-isoform-plasma • https://www.ultalabtests.com/test/cardio-iq-apoe-genotype-test

References

• FDA clearance (May 16, 2025) for first Alzheimer’s blood test (p‑tau217/β‑amyloid 1‑42 plasma ratio). U.S. Food and Drug Administration
• Alzheimer’s Association Clinical Practice Guideline on BBMs (released July 29, 2025). aaic.alz.orgAlzheimer's Journals
• Clinical performance of plasma p‑tau217 and Aβ42/40 combinations. PMC+1
• CKD/eGFR considerations for plasma p‑tau217 interpretation. PMC
• Transformative potential and accessibility of blood‑based biomarkers. Nature
• Supportive markers (NfL, GFAP) in Alzheimer’s and neurodegeneration. PMC+1
• Other commercial options: PrecivityAD2 (C2N), Simoa p‑tau217 (Quanterix), AlzoSure Predict(Diadem/Quest partnership). PMCC2N DiagnosticsQuanterix