What laboratory tests should be ordered for an adult or geriatric patient presenting with memory changes?

Laboratory Testing for Memory Changes

All patients presenting with memory changes should undergo a core "cognitive lab panel" including TSH, vitamin B12, homocysteine, complete blood count (CBC), and comprehensive metabolic panel (CMP), as these tests identify common comorbid conditions that can decompensate cognitive function and are potentially treatable. 1

Tier 1: Mandatory Laboratory Tests for All Patients

The following tests should be obtained in virtually all patients evaluated for memory changes due to their low cost, wide availability, and acceptable yield:

• Thyroid-Stimulating Hormone (TSH): Screens for hypothyroidism, a common and reversible cause of cognitive impairment in older adults 1, 2

• Vitamin B12: Identifies B12 deficiency, which can cause dementia that substantially improves with treatment 1, 2

• Homocysteine: Detects functional B12 deficiency that may not be captured by serum B12 levels alone, as hyperhomocysteinemia is associated with neuropsychiatric symptoms 1

• Complete Blood Count (CBC): Screens for anemia and infection as potentially reversible causes 2

• Comprehensive Metabolic Panel (CMP): Evaluates electrolyte disturbances, renal function, glucose abnormalities, and hepatic function—all potentially reversible causes 2

  • Liver function tests (ALT, AST) are particularly important as hepatic encephalopathy can present with attention deficits and forgetfulness 2

• Hemoglobin A1c: Evaluates diabetes control, as poor glycemic control contributes to cognitive impairment 2

Critical Accompanying Assessment

Laboratory testing alone is insufficient—you must pair it with validated cognitive testing (MoCA, Mini-Cog, or MMSE) to establish objective cognitive impairment. 2 Subjective memory complaints without objective testing can miss significant pathology, as diminished insight is common in cognitive disorders 2

Tier 1: Mandatory Neuroimaging

• Brain MRI without contrast is the preferred initial imaging modality to evaluate for structural causes including stroke, white matter disease, atrophy patterns, hydrocephalus, and space-occupying lesions 1, 2
  • MRI is superior to CT for detecting vascular lesions, hippocampal atrophy, and subtle structural abnormalities 2
  • If MRI is contraindicated or unavailable, non-contrast CT with coronal reformations is acceptable 1, 2

Tier 2-3: Specialized Testing (Selected Cases Only)

These tests should be reserved for specific clinical scenarios, not routine use:

• Cerebrospinal Fluid (CSF) Analysis: Consider in patients with early-onset dementia (<65 years), rapidly progressive dementia, or when autoimmune/infectious/paraneoplastic causes are suspected 1, 2, 3

  • CSF Alzheimer's biomarkers (Aβ42/Aβ40 ratio, p-tau181, t-tau) can identify or exclude AD as the underlying cause in diagnostically uncertain cases 2

• Blood Biomarkers for Amyloid Pathology: Emerging tools that may reduce need for CSF or PET imaging in appropriate clinical contexts (patients with objective cognitive impairment where AD is suspected after comprehensive workup) 2

• Advanced Imaging (FDG-PET, Amyloid PET): Reserved for diagnostically uncertain cases after specialist evaluation, not for initial primary care workup 1

Common Pitfalls to Avoid

• Do not dismiss subjective forgetfulness as "normal aging" without objective assessment, as changes common with advancing age are not always normal and warrant diagnostic evaluation 2

• Do not rely solely on patient self-report—obtain collateral information from a knowledgeable informant using standardized tools (AD8, IQCODE), as patients often lack insight into their cognitive decline 2

• Do not order extensive specialized testing routinely—additional testing beyond the core panel has little diagnostic impact in most cases and should be reserved for non-Alzheimer's presentations or diagnostically uncertain cases 4

Clinical Context Matters

The frequency of potentially reversible conditions is substantial: studies show low vitamin B12 in 26.4% and hypothyroidism in 16.5% of patients presenting with memory complaints 5. Concomitant conditions or risk factors with potential influence on cognitive function are identified in 61% of patients 6. This underscores why the core laboratory panel is essential for all patients—you are not just diagnosing dementia, you are identifying treatable contributors to cognitive decline.