What labs should be checked in a patient with a family history of Alzheimer's disease?

Laboratory Tests for Patients with Family History of Alzheimer's Disease

For patients with a family history of Alzheimer's disease, a multi-tiered laboratory approach is recommended, starting with Tier 1 laboratory tests including CBC with differential, comprehensive metabolic panel, thyroid function, vitamin B12, homocysteine, and inflammatory markers. 1

Tier 1 Laboratory Tests (Recommended for All Patients)

The Alzheimer's Association Clinical Practice Guidelines recommend the following basic laboratory panel for cognitive evaluation:

• Complete blood count (CBC) with differential
• Comprehensive metabolic panel (including renal and hepatic panels, electrolytes, glucose, calcium, magnesium, and phosphate)
• Thyroid-stimulating hormone (TSH)
• Vitamin B12 level
• Homocysteine level
• Inflammatory markers (C-reactive protein and erythrocyte sedimentation rate) 1

Neuroimaging

In addition to laboratory tests, structural brain imaging is strongly recommended:

• MRI (preferred) or CT (if MRI is contraindicated) 1
• Structural imaging helps exclude non-Alzheimer's conditions and may show evidence of regional brain atrophy consistent with neurodegenerative disease 1

Advanced Testing (When Indicated)

For patients with concerning symptoms or strong family history, additional testing may be considered:

• Amyloid biomarkers (PET or CSF) 1
• Tau biomarkers (CSF phosphorylated tau species) 1
• Blood-based biomarkers for Alzheimer's disease (emerging option) 1
• Metabolic testing (particularly if metabolic disorders are suspected) 2

Risk Assessment Considerations

When evaluating patients with family history of Alzheimer's disease, consider:

• Age (increased risk with advancing age)
• Education level (lower education associated with increased risk)
• Cerebrovascular risk factors (hypertension, diabetes, dyslipidemia)
• Medication review (especially anticholinergics or sedatives)
• Psychiatric conditions (particularly depression) 3

Common Pitfalls to Avoid

1. Not performing basic metabolic screening - Metabolic disorders can contribute to cognitive decline and may be modifiable risk factors 2, 4
2. Focusing only on Alzheimer's biomarkers - Other treatable conditions may cause or contribute to cognitive symptoms
3. Overlooking thyroid dysfunction - Thyroid disorders can present with cognitive symptoms that mimic dementia
4. Neglecting vitamin B12 deficiency - A reversible cause of cognitive impairment that should always be assessed

Testing Algorithm

1. Start with Tier 1 laboratory tests and structural brain imaging for all patients with family history of Alzheimer's disease
2. If cognitive symptoms are present, add validated cognitive assessment tools
3. If initial tests are normal but concerns persist, consider referral to a specialist for advanced biomarker testing
4. For patients with strong genetic risk (multiple affected first-degree relatives with early-onset disease), consider genetic counseling and testing 1, 3

The laboratory evaluation should be tailored based on the patient's age, symptom presentation, and specific family history pattern, with more comprehensive testing for those with multiple affected relatives or early-onset disease in the family.