What bloodwork is recommended for dementia screening?

Recommended Bloodwork for Dementia Screening

Blood tests are not used as primary screening tools for dementia but are essential for ruling out reversible causes of cognitive impairment after cognitive testing suggests impairment. 1, 2

Standard Laboratory Tests for Dementia Evaluation

When cognitive assessment indicates potential impairment, the following blood tests should be ordered:

First-Line Laboratory Tests (Essential)

• Complete blood count (CBC)
• Comprehensive metabolic panel
• Thyroid function tests (TSH, free T4)
• Vitamin B12 level
• Folate level
• Glucose level 2

Rationale for These Tests

These tests target the most common reversible causes of cognitive impairment:

• Thyroid dysfunction (prevalence 2.6% in dementia patients) 3
• Vitamin B12 deficiency (prevalence 1.7% in dementia patients) 3
• Folate deficiency (prevalence 0.4% in dementia patients) 3
• Metabolic abnormalities (sodium, calcium, glucose disturbances) 4

Additional Tests to Consider in Specific Situations

Based on clinical suspicion and risk factors, consider:

• Syphilis serology (VDRL/RPR) - if risk factors present 3
• HIV testing - if risk factors present
• Liver function tests - if history of alcohol use or liver disease
• Parathyroid hormone - if calcium abnormalities detected 4

Important Clinical Context

1. Blood tests alone cannot diagnose dementia

   • Cognitive testing remains the cornerstone for objectively assessing memory impairment 2
   • Blood tests primarily rule out reversible causes 1

2. Truly reversible dementias are rare

   • Only 1.7% of dementia cases show clinical improvement after treating metabolic causes 3
   • Most improvement occurs in cases of depression, normal pressure hydrocephalus, or subdural hematoma 3

3. Diagnostic efficiency

   • A selective approach using screening blood tests based on history and examination can reduce diagnostic costs by 66-75% compared to extensive testing 4

Emerging Blood-Based Biomarkers

For specialized memory clinics only (not recommended for primary care or routine screening):

• Plasma p-tau (particularly p-tau181)
• Plasma Aβ42/Aβ40 ratio
• Neurofilament light chain (NfL)
• Glial Fibrillary Acidic Protein (GFAP) 1, 2

These newer biomarkers should currently only be used in symptomatic patients at specialist clinics, and results should be confirmed with CSF or PET imaging whenever possible. Additional data are needed before using these as stand-alone diagnostic markers 1.

Clinical Approach Algorithm

1. First perform cognitive screening using validated tools (Mini-Cog, MMSE, MoCA) 2
2. If cognitive impairment is detected, order the standard laboratory panel
3. Interpret results in context of clinical presentation
4. Consider neuroimaging (MRI preferred, or non-contrast CT) if indicated 2
5. Refer to specialty care if diagnosis remains unclear after initial evaluation

Common Pitfalls to Avoid

• Relying solely on blood tests for dementia diagnosis
• Failing to order thyroid and B12 testing, which can detect clinically non-apparent but potentially treatable causes 3
• Ordering extensive testing without clinical indication
• Not following up on abnormal results with appropriate interventions
• Assuming all cognitive impairment with metabolic abnormalities will reverse with treatment

Remember that while blood tests are important for identifying potentially reversible causes, they are just one component of a comprehensive dementia evaluation that should include cognitive assessment, clinical history, and appropriate neuroimaging.