What blood tests are recommended for a geriatric patient presenting with symptoms of dementia?

Blood Tests for Dementia Evaluation

Essential Laboratory Screening Panel

All geriatric patients presenting with cognitive symptoms should undergo a standardized laboratory workup to identify reversible causes of dementia, including complete blood count, comprehensive metabolic panel (with particular attention to sodium, calcium, and glucose), thyroid function tests (TSH), and vitamin B12 and folate levels. 1, 2, 3

Core Laboratory Tests (Order for All Patients)

• Complete blood count (CBC) with differential to detect anemia, infection, or hematologic disorders that may contribute to cognitive impairment 1, 2, 3
• Comprehensive metabolic panel including electrolytes (especially sodium), calcium, glucose, blood urea nitrogen, creatinine, and liver function tests to identify metabolic encephalopathies 1, 2, 3, 4
• Thyroid-stimulating hormone (TSH) to screen for hypothyroidism, which is a common reversible cause of dementia 1, 2, 3, 5
• Vitamin B12 level to detect deficiency that can cause or contribute to cognitive decline 1, 2, 3, 5
• Folate level to identify folate deficiency as a potential contributor 1, 2, 3
• Homocysteine level when B12 or folate deficiency is suspected, as it provides additional diagnostic information 2

Selective Laboratory Tests (Based on Clinical Suspicion)

• Syphilis serology (RPR or VDRL) if there is clinical suspicion based on history, risk factors, or atypical presentation 3
• HIV testing in patients with risk factors or atypical dementia presentation 6
• Erythrocyte sedimentation rate (ESR) or C-reactive protein (CRP) if inflammatory or vasculitic processes are suspected 3

Blood-Based Biomarkers for Alzheimer's Disease

For patients being evaluated for disease-modifying therapy eligibility, blood-based biomarkers (BBMs) for amyloid pathology can serve as a triaging tool before proceeding to confirmatory CSF or amyloid PET testing. 1

When to Consider Blood Biomarkers

• Primary care setting: Patients typically aged ≥55 years with cognitive symptoms where Alzheimer's disease is suspected and disease-modifying therapy is being considered 1
• After initial workup: BBM testing should only occur after completing medical history, cognitive screening, depression screening, and standard laboratory tests to rule out reversible causes 1
• Interpretation context: BBM results must be interpreted alongside all clinical data, as certain conditions (obesity, chronic kidney disease) and medications (secubitril/valsartan) can influence biomarker concentrations 1

Blood Biomarker Performance Standards

• Positive BBM result (indicating likely AD-related amyloid pathology) should prompt referral to a dementia specialist for confirmatory testing with CSF analysis or amyloid PET scan before initiating disease-modifying therapy 1
• Negative BBM result (indicating unlikely AD pathology) suggests alternative etiologies should be pursued 1

Critical Implementation Points

Timing and Sequence

The laboratory workup should occur simultaneously with cognitive screening and functional assessment, not as a sequential step, to expedite diagnosis 2, 7. The standard metabolic and hematologic tests take priority over specialized biomarkers, as they identify immediately treatable conditions 1, 4.

Cost-Effectiveness Considerations

A selective approach based on history and physical examination findings is more cost-effective than ordering all possible tests routinely. The core panel (CBC, metabolic panel, TSH, B12, folate) would have identified 100% of treatable metabolic causes in prospective studies, with estimated charges 25-34% lower than comprehensive "shotgun" testing 4.

Common Pitfalls to Avoid

• Do not skip the core laboratory panel even if cognitive testing strongly suggests Alzheimer's disease, as up to 9.5% of dementia cases are due to reversible causes like medication toxicity or metabolic derangements 4
• Do not order blood-based AD biomarkers without first completing the standard dementia workup, as this may miss treatable conditions 1
• Do not interpret isolated laboratory abnormalities without clinical correlation—mild TSH elevation or borderline B12 levels require assessment in the context of symptoms and other findings 2, 3
• Do not use blood biomarkers as standalone diagnostic tests for Alzheimer's disease; they require confirmatory CSF or PET testing before initiating disease-modifying therapies 1

Integration with Other Assessments

Laboratory testing represents only one component of the comprehensive dementia evaluation. It must be combined with detailed history from a reliable informant, validated cognitive screening (MoCA or MMSE), functional assessment (FAQ or Lawton-Brody IADL), behavioral screening (NPI-Q), and structural neuroimaging (preferably MRI) 1, 2, 7.