From the Guidelines
When evaluating a patient with dementia, the indicated laboratory tests include thyroid function tests, vitamin B12, homocysteine, complete blood count with differential, complete metabolic panel, erythrocyte sedimentation rate, and C-reactive protein, as recommended by the most recent and highest quality study 1. These tests are essential to rule out potentially reversible causes of cognitive decline and identify comorbidities that may be contributing to the patient's dementia. The study published in the Journal of Internal Medicine in 2021 1 provides practical recommendations for the diagnosis of symptomatic Alzheimer's disease and dementia in primary care, emphasizing the importance of a comprehensive diagnostic assessment.
Key laboratory tests to consider include:
- Thyroid function tests to rule out hypothyroidism, a potentially reversible cause of cognitive impairment
- Vitamin B12 and homocysteine levels to identify vitamin deficiencies that may be contributing to cognitive decline
- Complete blood count with differential to assess for anemia, infection, or other hematologic abnormalities
- Complete metabolic panel to evaluate liver and kidney function, as well as electrolyte imbalances
- Erythrocyte sedimentation rate and C-reactive protein to assess for inflammation or infection The study also recommends conducting a neurologic physical examination, assessing risk factors for cognitive decline, and evaluating for psychiatric conditions 1. Additionally, structural brain imaging with MRI (or head CT if MRI is contraindicated) is recommended to rule out other potential causes of cognitive impairment.
By ordering these laboratory tests and conducting a comprehensive diagnostic assessment, healthcare providers can identify potentially reversible causes of cognitive decline and develop an effective treatment plan to improve the patient's quality of life and reduce morbidity and mortality.
From the Research
Laboratory Tests for Dementia
The following laboratory tests are indicated in a patient with dementia:
- Thyroid-stimulating hormone (TSH) levels 2, 3, 4
- Vitamin B12 levels 2, 5, 3
- Complete blood cell count (CBC) 3
- Blood chemistry battery, including sodium, calcium, and glucose concentrations 3
- Structural neuroimaging with noncontrast computed tomography (CT) or magnetic resonance imaging (MRI) 2, 6, 4
- Electroencephalography (EEG) as clinically indicated 4
Rationale for Laboratory Tests
These laboratory tests are recommended to:
- Rule out treatable causes of dementia, such as hypothyroidism, vitamin B12 deficiency, and metabolic encephalopathies 2, 6, 3
- Identify underlying medical conditions that may be contributing to cognitive impairment 5, 3
- Provide a baseline measurement of cognitive function and monitor disease progression 2
Selective Use of Laboratory Tests
The use of laboratory tests should be guided by the patient's clinical history, physical examination, and brief cognitive testing 6, 4. Other diagnostic tests, such as functional neuroimaging, neuropsychologic testing, and measurement of biomarkers, may be useful in selected cases but are not recommended for routine use 6.