What blood tests are recommended for a confusion screen?

Blood Tests for Confusion Screen

The standard blood tests for a confusion screen should include complete blood count (CBC), comprehensive metabolic panel (CMP), thyroid function tests, vitamin B12 level, and inflammatory markers. 1

Core Laboratory Tests for Confusion Workup

First-Line Testing

• Complete Blood Count (CBC)

  • Evaluates for anemia, infection, or hematologic malignancies
  • Includes hemoglobin, hematocrit, white blood cell count with differential, and platelet count

• Comprehensive Metabolic Panel (CMP)

  • Assesses electrolyte abnormalities, renal function, liver function, and glucose levels
  • Includes sodium, potassium, calcium, glucose, BUN, creatinine, and liver enzymes

• Thyroid Function Tests

  • TSH and free T4 to evaluate for hypo/hyperthyroidism

• Vitamin B12 Level

  • Critical for neurologic function; deficiency can cause cognitive impairment

• Inflammatory Markers

  • Erythrocyte sedimentation rate (ESR)
  • C-reactive protein (CRP)

Second-Line Testing (Based on Clinical Suspicion)

• Serum Tryptase and Vitamin B12 Levels

  • May be elevated in certain myeloproliferative disorders 1

• Autoimmune Panel

  • Antinuclear antibodies (ANA)
  • Extractable nuclear antigen antibodies
  • Antiphospholipid antibodies
  • Antineutrophil cytoplasmic antibodies (ANCA) 1

• Infectious Disease Testing

  • HIV
  • Syphilis serology (RPR/VDRL)
  • Lyme disease serology (when geographically relevant)

Special Considerations for Autoimmune Encephalitis

When autoimmune encephalitis is suspected, additional testing should include:

• Autoimmune Encephalopathy/Encephalitis Panel

  • Tests for neural autoantibodies (NAAs) in serum
  • Should be performed even if CSF is normal when clinical suspicion is high 1

• Additional Blood Tests

  • Antithyroid antibodies
  • Immunoglobulin levels
  • Metabolic and hormonal panels 1

Approach Based on Clinical Presentation

For Acute Confusion

1. Prioritize metabolic causes:

   • Glucose, electrolytes, renal function, liver function
   • Arterial blood gas if respiratory distress is present

2. Rule out infection:

   • CBC with differential
   • Blood cultures if febrile

3. Consider toxicology screen for medication effects or substance use

For Subacute or Chronic Confusion

1. Focus on nutritional and endocrine causes:

   • Vitamin B12, folate
   • Thyroid function tests
   • Consider homocysteine and methylmalonic acid if B12 deficiency suspected

2. Evaluate for inflammatory or autoimmune conditions:

   • ESR, CRP
   • Autoimmune panels as indicated

Monitoring Considerations

For patients in long-term care facilities with confusion, the American Thoracic Society recommends:

• Alert providers immediately for glucose values <70 mg/dL
• Notify providers for glucose values 70-100 mg/dL or >250 mg/dL within 24 hours 1

Common Pitfalls to Avoid

1. Not checking for medication effects - Always review complete medication list including over-the-counter preparations 2

2. Missing subclinical thyroid disease - Ensure proper thyroid function testing in all confused patients

3. Overlooking vitamin deficiencies - B12 deficiency can present with neuropsychiatric symptoms before hematologic abnormalities

4. Failing to repeat abnormal results - Confirm abnormal findings, especially when values are near diagnostic thresholds 1

5. Not considering age-specific normal ranges - Laboratory values may have different significance in older adults

By following this structured approach to blood testing in confused patients, clinicians can efficiently identify common reversible causes of confusion while appropriately escalating to more specialized testing when indicated.