What blood tests are recommended for diagnosing Alzheimer's disease?

Blood Tests for Alzheimer's Disease Diagnosis

Blood tests alone are not currently recommended as stand-alone diagnostic tests for Alzheimer's disease and should be used as part of a multi-tiered laboratory approach, with confirmation by cerebrospinal fluid (CSF) or positron emission tomography (PET) whenever possible. 1, 2

Tier 1 Laboratory Tests (Recommended for All Patients)

• A basic "cognitive lab panel" should be obtained in all patients with suspected cognitive or behavioral symptoms, including: 1
  • Complete blood count (CBC) with differential
  • Comprehensive metabolic panel (electrolytes, glucose, calcium, magnesium, phosphate)
  • Renal and hepatic function tests
  • Thyroid-stimulating hormone (TSH)
  • Vitamin B12 level
  • Homocysteine level
  • Inflammatory markers (C-reactive protein, erythrocyte sedimentation rate)

Structural Brain Imaging (Essential Component)

• Structural brain imaging should be obtained in almost all patients as part of Tier 1 testing: 1
  • MRI without contrast is preferred when available
  • CT scan should be considered when MRI is contraindicated

Emerging Blood-Based Biomarkers

• Plasma biomarkers for Alzheimer's disease are promising but not currently recommended for routine clinical use without confirmation by CSF or PET: 1, 2
  • Plasma phosphorylated tau (p-tau) variants (p-tau181, p-tau217, p-tau231) show high diagnostic accuracy but require further validation 2
  • Amyloid-β (Aβ) markers in blood are being developed but need standardization 1

Appropriate Use of Blood-Based Biomarkers

• Blood-based biomarkers may be cautiously used in specialized memory clinics as part of the diagnostic workup, but not as stand-alone tests 1, 2
• Results should be confirmed whenever possible with CSF or PET 1, 2
• The sensitivity and specificity of blood biomarker tests should be approximately 90% for amyloid PET status to be considered acceptable 1

Common Pitfalls to Avoid

• Relying solely on blood tests without comprehensive clinical assessment 2, 3
• Failing to confirm blood test results with CSF or PET when possible 1, 2
• Overlooking medical conditions that can influence biomarker interpretation 4, 3

Future Directions

• Plasma biomarkers show promise for pre-screening in clinical trials and may eventually be used in primary care settings 1, 5
• Recent research shows high diagnostic accuracy (88-92%) for plasma p-tau217 and amyloid markers in both primary and secondary care settings 5
• Standardized protocols for blood sample collection, processing, and storage are being developed 1, 2

Clinical Implementation Considerations

• Blood-based biomarkers could potentially improve diagnostic accuracy compared to clinical examination alone (91% vs 61-73% in recent studies) 5
• The prevalence of reversible causes of dementia is likely lower than previously believed, supporting a selective approach to investigations 6
• A careful history and physical examination accompanied by the recommended Tier 1 laboratory tests would be effective in diagnosing most treatable illnesses causing cognitive impairment 7, 6