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

Laboratory Evaluation for Altered Mental Status

For patients presenting with altered mental status, a comprehensive laboratory workup should include complete blood count, basic metabolic panel, liver function tests, urinalysis, thyroid function tests, and toxicology screening as the core diagnostic tests.

Initial Laboratory Assessment

Core Laboratory Tests

• Complete Blood Count (CBC) - To evaluate for infection, anemia, or other hematologic abnormalities 1
• Basic Metabolic Panel (BMP) - To assess electrolyte disturbances, renal function, and glucose levels 1
• Liver Function Tests (LFTs) - To evaluate for hepatic encephalopathy or other liver-related causes 1
• Urinalysis - Particularly high-yield in elderly patients to detect urinary tract infections, which are common causes of altered mental status 1
• Thyroid Function Tests (TSH) - To rule out thyroid disorders that can present with mental status changes 2, 1
• Toxicology Screen - To identify substance use or medication effects 2, 1

Additional Tests Based on Clinical Suspicion

• Blood Alcohol Level - When intoxication is suspected 1
• Ammonia Level - For patients with known cirrhosis or suspected hepatic encephalopathy 1
• Vitamin B12 Level - Particularly in elderly patients or those with malnutrition 2, 1
• Blood Cultures - If fever is present or infection is suspected 1
• HIV Testing - In patients with risk factors or unexplained neurological symptoms 1
• Erythrocyte Sedimentation Rate (ESR) and C-Reactive Protein (CRP) - To evaluate for inflammatory conditions 2

Imaging Studies

• Brain MRI (or CT if MRI is unavailable or contraindicated) - Indicated when no clear cause is identified from laboratory tests, when focal neurologic deficits are present, or when there is a history of trauma 2, 1
• EEG - Consider when seizures or nonconvulsive status epilepticus is suspected 1

Etiology-Specific Considerations

Medical Conditions

Multiple medical conditions can present with altered mental status, including:

• Neurological causes (28% of cases) - Stroke, seizures, CNS infections 3, 4
• Toxicological causes (21-23% of cases) - Medication effects, substance use 3, 4
• Infectious causes (9-10% of cases) - UTIs, pneumonia, sepsis, meningitis 3, 4
• Metabolic/Endocrine causes (5-8% of cases) - Electrolyte abnormalities, thyroid disorders, hypoglycemia 3, 4

Psychiatric vs. Organic Causes

While psychiatric conditions can present with altered mental status, it's crucial to rule out organic causes first:

• The American Academy of Child and Adolescent Psychiatry emphasizes that all patients with psychotic symptoms should receive thorough medical evaluation 2
• Laboratory tests should be justified based on clinical presentation and significant findings in history or physical examination 2

Common Pitfalls to Avoid

• Premature attribution to psychiatric causes without adequate medical workup 1
• Overreliance on neuroimaging before basic laboratory testing 1
• Missing atypical presentations of common infections in elderly patients 1
• Failure to recognize medication side effects or interactions 1

Evidence-Based Approach

Multiple studies have questioned the utility of routine extensive laboratory testing in all patients with psychiatric symptoms. However, for true altered mental status:

• A systematic approach focusing on potentially life-threatening reversible causes is essential 5
• The patient history and physical examination have been found to be most useful diagnostically, with laboratory investigations providing critical information in specific scenarios 4
• Selective testing guided by clinical evaluation is more efficient than extensive routine testing 2

Laboratory Testing Algorithm

1. For all patients with altered mental status:

   • CBC, BMP, LFTs, urinalysis, TSH
   • Consider toxicology screen based on clinical suspicion

2. Add based on specific clinical features:

   • Fever → Blood cultures, CSF analysis if meningeal signs present
   • History of liver disease → Ammonia level
   • Suspected vitamin deficiency → B12, folate levels
   • Risk factors for HIV → HIV testing
   • Suspected inflammatory condition → ESR, CRP

3. Proceed to imaging if:

   • Laboratory tests don't reveal a clear cause
   • Focal neurological deficits are present
   • History of trauma
   • Persistent unexplained altered mental status

By following this systematic approach to laboratory evaluation, clinicians can efficiently identify the underlying cause of altered mental status and initiate appropriate treatment to improve outcomes related to morbidity, mortality, and quality of life.