What blood tests are recommended for someone with a history of alcohol (ethanol) use presenting with worsening cognition?

Blood Tests for Worsening Cognition in Patients with Alcohol Use History

In patients with a history of alcohol use presenting with worsening cognition, a comprehensive Tier 1 laboratory panel should be obtained, including complete blood count, comprehensive metabolic panel, thyroid function, vitamin B12 levels, homocysteine, and inflammatory markers (CRP and ESR). 1

Primary Laboratory Panel

The Alzheimer's Association clinical practice guidelines recommend a multi-tiered approach to laboratory testing for cognitive impairment, with the following Tier 1 tests being essential:

• Complete blood count (CBC) with differential
• Comprehensive metabolic panel including:
  • Renal function (BUN, creatinine)
  • Hepatic panel
  • Electrolytes
  • Glucose
  • Calcium, magnesium, phosphate
• Thyroid-stimulating hormone (TSH)
• Vitamin B12 level
• Homocysteine level
• C-reactive protein (CRP)
• Erythrocyte sedimentation rate (ESR) 1

Alcohol-Specific Biomarkers

For patients with alcohol use history, additional alcohol-specific biomarkers should be included:

• Phosphatidylethanol (PEth) - highly sensitive and specific biomarker that can detect alcohol use for up to 6 weeks 1, 2
• Gamma-glutamyltransferase (GGT) - sensitive but less specific marker 2
• AST/ALT ratio - typically >2 in alcohol-related liver disease 2
• Carbohydrate-deficient transferrin (CDT) - specific for chronic alcohol use 2

Thiamine Assessment

Given the strong association between alcohol use and thiamine deficiency:

• Thiamine level assessment is crucial as deficiency can cause cognitive impairment and Wernicke-Korsakoff syndrome 3, 4
• Parenteral thiamine supplementation (250-500mg/day) should be considered in patients at high risk of deficiency 3

Additional Considerations

For patients with suspected hepatic encephalopathy (common in alcohol-related liver disease):

• Ammonia levels may be helpful, though hyperammonemia can occur without encephalopathy 1
• Liver function tests should be carefully evaluated, as an AST/ALT ratio >2 is highly suggestive of alcohol-related liver disease 2

Diagnostic Algorithm

1. Initial assessment:

   • Obtain comprehensive Tier 1 laboratory panel
   • Add alcohol-specific biomarkers (PEth, GGT, AST/ALT ratio)
   • Assess thiamine status

2. If liver dysfunction is present:

   • Evaluate for hepatic encephalopathy with ammonia levels
   • Consider additional liver function tests

3. If vitamin deficiencies are suspected:

   • Add folate, vitamin D, and other B vitamin assessments
   • Consider nutritional consultation

4. If cognitive symptoms persist despite normal initial workup:

   • Consider structural brain imaging (MRI preferred, CT if MRI contraindicated) 1
   • Consider referral to neurology or neuropsychology for further evaluation

Important Caveats

• Normal laboratory values do not exclude alcohol-related cognitive impairment
• Cognitive testing should be integrated with laboratory findings for comprehensive assessment
• Alcohol withdrawal can cause cognitive symptoms and should be considered in the differential diagnosis 1
• Patients with alcohol use history may have multiple contributing factors to cognitive decline, including direct neurotoxicity, nutritional deficiencies, and liver disease 5

Remember that early detection of reversible causes of cognitive impairment in patients with alcohol use history can prevent progression to more severe and potentially irreversible conditions.