What labs should be included in the initial workup for a patient with acute altered mental status?

Initial Laboratory Workup for Acute Altered Mental Status

For patients with acute altered mental status, the initial laboratory workup should include blood glucose, complete blood count, basic metabolic panel, liver function tests, and urinalysis, with additional tests guided by clinical presentation rather than routine extensive testing. 1

Core Laboratory Tests

• Blood glucose measurement (immediate point-of-care testing)

  • Critical first step; if <70 mg/dL, administer IV glucose immediately 1

• Basic metabolic panel

  • Electrolyte abnormalities (sodium, potassium, calcium)
  • Renal function (BUN, creatinine)
  • Acid-base disturbances 1

• Complete blood count

  • Evaluate for infection, anemia, and other hematologic abnormalities 1

• Liver function tests

  • Rule out hepatic encephalopathy and liver dysfunction 1

• Urinalysis

  • Screen for urinary tract infection, a common cause of altered mental status especially in elderly patients 1

Additional Tests Based on Clinical Suspicion

• Blood cultures if fever present 1
• Thyroid function tests if thyroid disorder suspected 1
• Toxicology screen when substance use is suspected, though routine screening is not supported by evidence 2
  • Note: Urine drug screens have only 20% sensitivity for organic etiology of psychiatric complaints 2

Neuroimaging Considerations

• Head CT without contrast is usually the first-line neuroimaging test when indicated 2, 1

  • Particularly indicated for:
    • Patients on anticoagulants
    • Suspected intracranial bleeding
    • Hypertensive emergency
    • Suspicion for intracranial infection, mass, or elevated pressure 2

• Brain MRI may be preferred when:

  • Clinical picture is unclear
  • Presentation is atypical
  • Abnormal findings on examination 1

High-Risk Populations Requiring More Extensive Testing

Several studies have identified groups that may require more comprehensive evaluation:

• Elderly patients 2, 3
• Patients with substance abuse history 2
• Patients without prior psychiatric history presenting with new psychiatric symptoms 2
• Patients with new or preexisting medical complaints 2
• Those of lower socioeconomic status 2

Clinical Pearls and Pitfalls

• Avoid routine extensive laboratory testing in all patients with psychiatric symptoms, as it has very low yield 2
• Direct diagnostic evaluation by history and physical examination rather than ordering a standard battery of tests 2
• Remember that delirium is a medical emergency with mortality rates twice as high if undiagnosed 1
• Consider the high mortality rate (8.1%) associated with altered mental status, particularly in elderly patients 1, 3
• Be aware that false-positive laboratory results can be 8 times more frequent than true positives in routine testing 2

The approach to altered mental status should be systematic but targeted based on clinical presentation, avoiding unnecessary testing while ensuring potentially life-threatening causes are not missed.