What biomarkers are recommended for evaluating dementia in patients in the Philippines, particularly in older adults (≥65 years) or younger individuals with a compatible clinical picture?

Biomarkers for Dementia Evaluation in the Philippines

For dementia evaluation in the Philippines, blood-based biomarkers (particularly plasma p-tau217, p-tau181, and Aβ42/40 ratio) should be prioritized as the primary biomarker approach, given the country's limited healthcare resources and high out-of-pocket costs that make CSF and PET imaging largely inaccessible. 1, 2

Recommended Biomarker Strategy

Core Blood-Based Biomarkers (First-Line)

The most recent guidelines establish a clear hierarchy of biomarkers for Alzheimer's disease diagnosis 1, 3:

• Core 1 Biomarkers (sufficient to establish AD diagnosis):
  • Plasma p-tau217 (highest accuracy, commercially available)
  • Plasma p-tau181 (widely validated)
  • Plasma Aβ42/40 ratio (detects amyloid pathology)

These blood-based biomarkers can be ordered in primary care settings and are particularly suited for the Philippines where specialist-to-population ratios are extremely low and healthcare costs are prohibitive 4. Plasma p-tau217 demonstrates the strongest correlation with core AD pathology and can detect amyloid pathology even before clinical symptoms emerge 5, 6.

Prognostic Biomarkers (Second-Line)

When available and affordable, these provide additional prognostic information 1:

• Plasma neurofilament light chain (NfL) - tracks neurodegeneration and disease progression
• Plasma glial fibrillary acidic protein (GFAP) - reflects astrocytic activation
• Plasma total tau (t-tau) - indicates neuronal injury

Clinical Application Algorithm

For patients ≥65 years with amnestic presentation:

1. Order plasma p-tau217 or p-tau181 as initial biomarker test
2. If positive → high likelihood of AD pathology; consider referral for disease-modifying therapy eligibility assessment
3. If negative → evaluate for non-AD dementias (vascular, Lewy body, frontotemporal)

For younger patients (<65 years) or non-amnestic presentations:

1. Blood-based biomarkers remain first-line due to accessibility
2. Lower pretest probability requires careful interpretation of positive results (higher false-positive risk) 2
3. Positive results warrant referral to specialist for comprehensive evaluation

Context-Specific Considerations for the Philippines

Resource Limitations

The Philippines faces severe constraints in dementia care 4:

• High out-of-pocket healthcare costs
• Limited health insurance coverage for advanced diagnostics
• Low specialist availability
• Minimal access to PET imaging and CSF analysis

Blood-based biomarkers directly address these barriers by offering:

• Lower cost compared to PET ($3,000-5,000) or CSF analysis
• Point-of-care or regional laboratory testing capability
• No need for specialized imaging centers or lumbar puncture expertise

Structural Imaging Role

While blood biomarkers should be prioritized, brain MRI or CT remains essential to exclude:

• Vascular dementia (infarcts, white matter disease)
• Structural lesions (tumors, subdural hematomas)
• Normal pressure hydrocephalus

Order structural imaging concurrently with blood biomarkers when accessible 2. However, do not delay biomarker testing if imaging has long wait times.

Important Caveats

Interpretation Pitfalls

1. Kidney function affects biomarker levels: Impaired kidney function (eGFR <60) elevates p-tau181, p-tau217, NfL, and GFAP levels without necessarily indicating dementia 7. Check renal function when interpreting results.

2. Age-related considerations: AD pathology prevalence increases with age in asymptomatic individuals, reducing specificity of positive biomarkers in very elderly patients 8.

3. Mixed pathologies: Blood biomarkers primarily detect AD pathology but may not identify coexisting vascular or Lewy body pathology 5. Clinical correlation remains essential.

When Blood Biomarkers Are Insufficient

Refer to specialist when:

• Blood biomarkers conflict with clinical presentation
• Non-amnestic presentations suggesting frontotemporal dementia or primary progressive aphasia
• Rapid onset suggesting vascular or infectious etiology
• Features of Lewy body dementia (visual hallucinations, parkinsonism, REM sleep behavior disorder)

Biomarker Availability

Several assays are now commercially available for research and clinical use 5:

• ALZpath p-tau217 assay
• Fujirebio plasma p-tau217 assay
• Various p-tau181 platforms

Primary care physicians in the Philippines should advocate for local laboratory adoption of these platforms to improve accessibility and reduce costs through economies of scale.

Disease-Modifying Therapy Considerations

With anti-amyloid therapies now available, accurate biomarker diagnosis becomes critical for treatment eligibility 2. Blood-based biomarkers serve as effective triaging tools:

• Positive blood biomarker → consider referral for confirmatory testing (if DMT being considered)
• APOE genotyping should occur after confirmatory testing, not as initial screen 2

The practical reality in the Philippines is that most patients will not access disease-modifying therapies due to cost, but biomarkers still provide diagnostic clarity, prognostic information, and guide symptomatic management strategies 4.