Dementia Screening Blood Test
No, a blood test alone is not sufficient for diagnosing dementia—blood tests serve only to exclude reversible causes of cognitive impairment, not to diagnose dementia itself. 1, 2
Role of Blood Tests in Dementia Evaluation
Blood tests are not screening tools for dementia but rather part of the diagnostic workup after cognitive impairment is detected through clinical assessment. 1, 3
Core laboratory tests recommended include:
- Complete blood count 4, 3
- Comprehensive metabolic panel (specifically sodium, calcium, glucose) 4, 3
- Thyroid function tests (TSH) 4, 3
- Vitamin B12 level 3
These tests identify treatable causes of cognitive impairment such as hypothyroidism, metabolic encephalopathies (hyponatremia, hyperparathyroidism, hypoglycemia), and B12 deficiency—not dementia itself. 4, 3
Actual Dementia Diagnosis Requires
Dementia diagnosis is fundamentally clinical, requiring: 5, 2
- History from patient AND informant documenting cognitive decline affecting daily function 5, 2
- Mental status examination by clinician assessing memory, language, attention, visuospatial function, executive function 5, 2
- Brief cognitive screening tools (Mini-Cog preferred: 2-4 minutes, 76% sensitivity, 89% specificity) 6, 7
- Physical and neurological examination to identify focal deficits suggesting stroke or other pathology 5, 3
- Structural brain imaging (CT or MRI) in selected cases to rule out treatable causes like tumor or identify cerebrovascular disease 2, 3
Critical Diagnostic Pitfall
The most common error is relying on any single test—blood or cognitive—to diagnose dementia. 7, 8 Screening scores alone are not diagnostic and must be interpreted within comprehensive clinical context including functional assessment and corroborated history. 6, 7
When to Pursue Evaluation
Evaluate patients with: 6
- Self-reported cognitive concerns
- Family-reported concerns about memory or function
- Observed difficulties with appointments, medication adherence, or decision-making
- Advanced age (prevalence 5% ages 71-79, rising to 37% over age 90) 6
Screening asymptomatic older adults is not recommended as no trials demonstrate that routine screening improves mortality, quality of life, or functional outcomes. 6