What labs should be ordered for a patient presenting with global altered mental status?

Laboratory Evaluation for Global Altered Mental Status

For patients presenting with global altered mental status, diagnostic evaluation should be directed by the history and physical examination rather than routine laboratory testing of all patients, as this approach has very low yield. 1

Initial Laboratory Workup

First-Tier Tests (Obtain in all patients)

• Complete blood count (CBC) - to evaluate for infection and anemia
• Basic metabolic panel (BMP) - to assess electrolyte abnormalities, renal function
• Liver function tests - to evaluate for hepatic encephalopathy
• Thyroid stimulating hormone (TSH) - to rule out thyroid disorders
• Vitamin B12 levels - to assess for deficiency
• Urinalysis - to evaluate for urinary tract infection
• Toxicology screen - for substance-related causes
• Glucose measurement - to rule out hypoglycemia or hyperglycemia

Second-Tier Tests (Based on clinical suspicion)

• Blood cultures - if fever or signs of infection are present
• Ammonia levels - if hepatic encephalopathy is suspected
• Arterial blood gas - if hypoxia or acid-base disturbance is suspected
• C-reactive protein or ESR - to evaluate for inflammatory conditions
• HIV testing - particularly in at-risk populations
• RPR/VDRL - to evaluate for neurosyphilis
• Lyme antibody - in endemic areas or with relevant history

Neuroimaging

• Brain MRI (or CT if MRI is unavailable or contraindicated) should be performed when:
  • Focal neurological deficits are present
  • New or worsening headaches
  • History of head trauma
  • First-episode altered mental status without clear cause
  • Atypical presentation or age of onset 2

Additional Testing Based on Clinical Presentation

Lumbar Puncture

Indicated when:

• Infectious encephalitis/meningitis is suspected
• Autoimmune encephalitis is considered
• Subarachnoid hemorrhage is suspected but neuroimaging is negative
• CSF analysis should include cell count, glucose, protein, and culture 2

Electroencephalogram (EEG)

Indicated when:

• Seizures or non-convulsive status epilepticus are suspected
• Unexplained persistent altered mental status despite initial workup 2

Common Causes by Category

The most common causes of altered mental status include:

1. Neurological (35%) - stroke, seizures, CNS infections
2. Toxicological (23%) - medication effects, substance intoxication/withdrawal
3. Systemic/organic (14.5%) - organ failure, hypoxia
4. Infectious (9.1%) - sepsis, meningitis, encephalitis
5. Endocrine/metabolic (7.9%) - electrolyte disorders, thyroid dysfunction
6. Psychiatric (3.9%) - severe depression, psychosis
7. Traumatic (2.1%) - traumatic brain injury
8. Gynecologic/obstetric (1.9%) - eclampsia, postpartum conditions 3

Special Considerations

Elderly Patients

• More likely to have abnormal brain imaging
• Consider delirium workup with additional focus on:
  • Medication review (polypharmacy)
  • Evaluation for occult infection (UTI, pneumonia)
  • Assessment for metabolic derangements 2

Patients with Substance Use History

• More extensive toxicology screening
• Evaluation for withdrawal syndromes
• Assessment for complications of substance use (endocarditis, abscesses) 1

Common Pitfalls to Avoid

1. Attributing altered mental status to psychiatric causes without adequate medical workup - always rule out organic causes first 2
2. Failing to recognize non-convulsive status epilepticus - consider EEG in unexplained altered mental status
3. Missing subtle metabolic derangements - check electrolytes, glucose, renal and liver function
4. Overlooking medication effects - review all medications, particularly anticholinergics, sedatives, and opioids
5. Relying on routine laboratory testing without clinical correlation - false positive results are 8 times more common than true positives in undirected testing 1

By following this structured approach to laboratory evaluation, clinicians can efficiently identify the underlying cause of altered mental status and initiate appropriate treatment to improve patient outcomes.