What laboratory tests are recommended for diagnosing dementia?

Laboratory Tests for Diagnosing Dementia

For patients with suspected dementia, a standard laboratory workup should include complete blood count, comprehensive metabolic panel, thyroid function tests, and vitamin B12 levels to rule out reversible causes of cognitive impairment. 1, 2

Core Laboratory Tests

The following laboratory tests are recommended as part of the initial evaluation:

• Complete Blood Count (CBC) with differential 1, 3
• Comprehensive Metabolic Panel including:
  • Electrolytes (particularly sodium)
  • Glucose
  • Calcium
  • Renal function tests 1, 4
• Thyroid Function Tests (TSH) 1, 5, 3
• Vitamin B12 level 1, 5, 3

These core tests are supported by the Alzheimer's Association and American Academy of Neurology guidelines and are effective in diagnosing treatable illnesses that can cause cognitive impairment 1, 5.

Additional Tests Based on Clinical Presentation

Beyond the core tests, additional laboratory evaluations should be ordered selectively based on clinical suspicion:

• Syphilis serology (when clinically indicated) 4
• Folate level (especially in malnourished patients) 6
• Parathyroid hormone (if hypercalcemia is present) 5
• Toxicology screen (if medication or substance use is suspected) 2

Importance of Laboratory Testing in Dementia Evaluation

Laboratory tests play a critical role in identifying potentially reversible causes of dementia:

• Studies show that 1.5-3.5% of patients with cognitive impairment have abnormal metabolic values that, when corrected, lead to clinical improvement 6
• The most common reversible causes identified through laboratory testing include:
  • Hypothyroidism
  • Metabolic encephalopathies due to hyponatremia
  • Hyperparathyroidism
  • Hypoglycemia
  • Vitamin B12 deficiency 5, 6

Beyond Laboratory Tests: Comprehensive Evaluation

While laboratory tests are essential, they should be part of a comprehensive diagnostic approach that includes:

• Neuroimaging: Brain MRI or non-contrast CT to evaluate structural causes, vascular disease, and patterns of atrophy 1, 3
• Cognitive Assessment: Using validated tools such as the Mini-Mental State Examination (MMSE), Montreal Cognitive Assessment (MoCA), or Mini-Cog 7, 1
• Functional Assessment: Using tools like the Functional Activities Questionnaire (FAQ) or Disability Assessment for Dementia (DAD) 7, 1

Clinical Pearls and Pitfalls

• Pearl: A selective approach to laboratory testing based on history and physical examination findings can reduce diagnostic costs by 25-34% compared to routine comprehensive testing 5
• Pitfall: Relying solely on laboratory tests without proper cognitive assessment and neuroimaging may miss the underlying cause of dementia
• Pearl: The majority (62.5%) of metabolic abnormalities causing cognitive impairment are previously unknown to patients and their physicians, highlighting the importance of laboratory screening 6
• Pitfall: Normal laboratory values do not exclude dementia; Alzheimer's disease and vascular dementia, the most common causes, are not diagnosed through laboratory testing 2

By following this structured approach to laboratory testing, clinicians can effectively identify potentially reversible causes of cognitive impairment while avoiding unnecessary tests.