Laboratory Testing for Forgetfulness
Order a comprehensive cognitive lab panel including TSH, vitamin B12, homocysteine, complete blood count, comprehensive metabolic panel (including liver function tests), and hemoglobin A1c for all patients presenting with forgetfulness. 1, 2
Tier 1: Mandatory Laboratory Tests
The following tests should be obtained in all or nearly all patients evaluated for forgetfulness, based on their low cost, wide availability, and acceptable yield for detecting common comorbid conditions that can cause or worsen cognitive symptoms:
Core Metabolic and Hematologic Panel
- Complete Blood Count (CBC) to screen for anemia and infection, both potentially reversible causes of cognitive impairment 2, 3
- Comprehensive Metabolic Panel to evaluate electrolyte disturbances, renal function, glucose abnormalities, and hepatic function 2, 3
- Liver function tests (ALT, AST) are particularly important as hepatic encephalopathy can present with attention deficits and forgetfulness 2, 3
Endocrine and Vitamin Assessment
- Thyroid-Stimulating Hormone (TSH) with free T4 if abnormal, as hypothyroidism is a common reversible cause of cognitive impairment in older adults 1, 2, 3
- Vitamin B12 levels to identify deficiency, which can cause dementia that substantially improves with treatment 1, 2, 3
- Homocysteine because hyperhomocysteinemia is associated with functional B12 deficiency and may not always be readily detected by B12 levels alone 1
Metabolic Risk Assessment
- Hemoglobin A1c (HbA1c) to evaluate diabetes control, as poor glycemic control contributes to cognitive impairment 2, 3
- Lipid panel for vascular risk stratification 2, 3
Essential Accompanying Assessments
Laboratory testing alone is insufficient and must be paired with:
- Validated cognitive screening using instruments such as the Montreal Cognitive Assessment (MoCA), Mini-Cog, or Mini-Mental State Examination (MMSE) to establish objective cognitive impairment 2, 3, 4
- Brain MRI (non-contrast preferred) to evaluate for stroke, white matter disease, atrophy patterns, hydrocephalus, and space-occupying lesions; CT is acceptable if MRI is contraindicated 2, 3, 4
- Corroborative informant history using validated questionnaires such as the AD8 or IQCODE, as diminished insight is common in cognitive impairment 3, 4
Tier 2-3: Specialized Testing (Selected Cases Only)
Consider additional testing based on specific clinical presentations:
- Lumbar puncture with CSF analysis for early-onset dementia (<65 years), rapidly progressive dementia, or when autoimmune/infectious/paraneoplastic causes are suspected 2, 3
- CSF Alzheimer's biomarkers (Aβ42/Aβ40 ratio, p-tau181, t-tau) for patients with mild dementia to identify or exclude AD as the underlying cause 2, 4
- Blood biomarkers for amyloid pathology are emerging tools that may reduce the need for CSF or PET imaging in appropriate clinical contexts (patients with objective cognitive impairment where AD is suspected after comprehensive workup) 1, 2
Critical Clinical Considerations
Do not dismiss forgetfulness as "normal aging" without objective assessment, as changes that may be common with advancing age are not always normal and warrant diagnostic evaluation. 2, 4
Common Pitfalls to Avoid
- Relying solely on patient self-report without informant corroboration leads to missed diagnoses due to lack of insight 4
- Failing to recognize that forgetfulness is non-specific and can be related to anxiety, depression, and somatic symptoms rather than dementia alone 1, 2
- Overlooking medical conditions that can influence cognitive function, including sleep disorders (particularly sleep apnea), sensory deficits (hearing loss, vision loss), and recent episodes of delirium 3, 4
Screening for High-Risk Conditions
Assess for conditions associated with cognitive disorders including history of stroke or TIA, late-onset depressive disorder, untreated sleep apnea, unstable metabolic or cardiovascular morbidity, recent episode of delirium, and recent head injury. 3, 4