What blood tests are recommended for evaluating memory issues?

Blood Tests for Memory Issues

When evaluating memory complaints, obtain basic laboratory screening tests including complete blood count, comprehensive metabolic panel, thyroid function tests (TSH), vitamin B12, and consider inflammatory markers (ESR, CRP) to exclude reversible causes of cognitive impairment. 1, 2

Essential Laboratory Screening Panel

The following blood tests should be ordered as part of the initial workup for memory concerns:

Core Laboratory Tests

• Complete blood count (CBC) with differential to rule out anemia and infection 2
• Comprehensive metabolic panel including electrolytes, calcium, magnesium, glucose, and liver function tests 2
• Thyroid-stimulating hormone (TSH) to exclude hypothyroidism 1, 2
• Vitamin B12 levels (with homocysteine and folate if B12 is low-normal) 1, 2, 3
• Inflammatory markers (erythrocyte sedimentation rate and C-reactive protein) 2, 3

Clinical Context

These basic blood tests serve to identify reversible or treatable causes of cognitive impairment rather than diagnosing specific neurodegenerative diseases like Alzheimer's disease. 1 Low vitamin B12 and hypothyroidism are found in approximately 26% and 17% of patients with memory complaints, respectively, making these screening tests particularly important. 4

Advanced Blood-Based Biomarkers for Alzheimer's Disease

Current Limitations and Appropriate Use

Blood-based biomarkers (BBMs) for Alzheimer's disease, particularly plasma phosphorylated tau (p-tau), should currently only be used in symptomatic patients at specialist memory clinics, and results should be confirmed with CSF analysis or amyloid PET imaging whenever possible. 1

Key Restrictions on Blood Biomarker Use

• Not ready for primary care: No studies have extensively validated BBMs for neurodegenerative diseases in primary care settings, and results from specialized memory clinics cannot be directly translated to primary care populations. 1
• Specialist setting only: BBMs with established thresholds should currently only be used in symptomatic patients at specialist clinics. 1
• Requires confirmation: Additional data are needed before use of BBMs as stand-alone diagnostic markers; they should be confirmed with CSF or PET. 1
• Not for screening: BBMs are not appropriate for asymptomatic individuals or general population screening. 1

When Advanced Biomarkers May Be Considered

Advanced biomarkers (including blood-based markers, CSF analysis for Aβ42, tau, and p-tau, or amyloid/tau PET imaging) may be considered in specialist settings for: 2, 3

• Clinically uncertain cases or atypical presentations 1, 3
• Rapid progression of symptoms 3
• Complex behavioral symptoms 3
• Predicting conversion from mild cognitive impairment to Alzheimer's dementia 1, 3

Complete Diagnostic Workup Beyond Blood Tests

Clinical Assessment Components

Blood tests are only one component of a comprehensive evaluation. The workup should also include: 1, 2

• Detailed history from patient and reliable informant using structured tools (AD8, Alzheimer's Questionnaire) 1, 2
• Cognitive testing with validated instruments (MoCA, MMSE, or Modified MMSE) 1, 3
• Functional assessment using FAQ or DAD scales 1, 3
• Neuropsychiatric evaluation including screening for depression and anxiety 2, 3
• Structural brain imaging (MRI preferred, or CT if contraindicated) 1, 2, 3

Medication Review

Evaluate for medications that can contribute to cognitive symptoms, particularly anticholinergics and sedative-hypnotics. 2, 3 This is a frequently overlooked reversible cause of cognitive impairment.

Common Pitfalls to Avoid

• Failing to obtain informant history: Corroborative history from a reliable informant is essential, as patients often lack insight into their cognitive decline. 1, 2
• Ordering advanced biomarkers prematurely: Blood-based Alzheimer's biomarkers should not be ordered in primary care or without specialist consultation. 1
• Missing reversible causes: Hypothyroidism, B12 deficiency, medication effects, depression, and sleep apnea are common and treatable. 2, 3, 4
• Overlooking comorbidities: Conditions like obesity, chronic kidney disease, diabetes, and cardiovascular disease can influence both cognitive function and biomarker interpretation. 1, 3

Referral Considerations

Refer to a neurologist, geriatrician, geriatric psychiatrist, or dementia subspecialist when: 2, 3

• Atypical presentations or rapid progression
• Age of onset under 65 years
• Complex behavioral symptoms
• Diagnostic uncertainty after initial workup
• Consideration of advanced biomarker testing