What laboratory tests should be ordered for a patient presenting with confusion?

Laboratory Testing for Confusion

All patients presenting with confusion require immediate point-of-care glucose testing, followed by a comprehensive metabolic panel, complete blood count, and additional targeted tests based on clinical context. 1

Immediate First-Line Testing (Tier 1)

Critical Immediate Test

• Finger-stick blood glucose must be performed immediately upon patient contact—hypoglycemia is rapidly reversible and can be fatal if missed, with signs frequently confused with intoxication or withdrawal 1
• If glucose <70 mg/dL, administer 30-50 g IV glucose urgently 1
• If unable to check glucose and patient has impaired mental state, administer IV glucose empirically 1

Essential Laboratory Panel

The following tests should be obtained routinely in all patients with confusion:

Complete Blood Count (CBC) with differential 2

• Identifies infection, anemia, and hematologic abnormalities that commonly contribute to altered mental status 3

Complete Metabolic Panel (Chem-20) including: 2

• Electrolytes (sodium, potassium, chloride, bicarbonate)
• Renal function (creatinine, eGFR)
• Hepatic panel (AST, ALT, bilirubin, albumin)
• Glucose
• Calcium, magnesium, phosphate

Thyroid-Stimulating Hormone (TSH) 2

• Thyroid dysfunction is a reversible cause of confusion

Vitamin B12 level 2

• Deficiency can cause cognitive impairment

Additional Tier 1 Tests (per Alzheimer's Association 2025 guidelines):

• Homocysteine level 2
• C-reactive protein (CRP) 2
• Erythrocyte sedimentation rate (ESR) 2

Context-Specific Testing

For Stroke Evaluation

If acute stroke is suspected, add: 2

• Coagulation studies (aPTT, INR) 2
• Troponin 2
• 12-lead ECG 2

For Cirrhosis/Liver Disease

When hepatic encephalopathy is considered: 2

• Metabolic assessment for precipitating factors
• Drug and alcohol levels 2
• Note: Routine ammonia levels are NOT recommended—a low ammonia should prompt investigation of alternative causes, but elevated levels are non-specific 2

Additional Targeted Tests

Based on clinical presentation, consider: 2, 3

• Urinalysis for infection 3
• Toxicology screen and blood alcohol level if substance use suspected 2
• Arterial blood gas if respiratory concerns 2
• Cardiac enzymes if myocardial ischemia suspected 2, 3
• Pregnancy test in women of childbearing age 2

Diagnostic Imaging

Brain imaging (CT or MRI) should be obtained selectively, not routinely: 2, 3

Indications for neuroimaging include:

• First episode of altered mental status 2
• Focal neurological deficits 2, 3
• Recent head trauma 3
• New-onset seizures 2, 3
• Signs of increased intracranial pressure 3
• Unsatisfactory response to treatment of precipitating factors 2

Do NOT obtain routine brain imaging for recurrent, non-focal presentations similar to prior episodes 2

Critical Pitfalls to Avoid

• Never assume intoxication without first ruling out hypoglycemia—clinical presentations overlap significantly and hypoglycemia can cause permanent brain damage 1
• Do not delay glucose testing to obtain neuroimaging first 1
• Confusion is a diagnosis of exclusion—always investigate for reversible causes including infections, medications, metabolic disturbances, and substance withdrawal 2, 3
• Avoid extensive routine laboratory batteries—testing should be guided by clinical evaluation rather than performed indiscriminately 3
• Do not routinely measure ammonia levels in cirrhotic patients—they are non-specific and do not guide management 2

Additional Diagnostic Considerations

• Chest radiography to evaluate for pneumonia or pulmonary processes 3
• ECG monitoring for more than 24 hours if cardiac arrhythmia suspected 2
• Lumbar puncture only if subarachnoid hemorrhage suspected and CT is negative 2
• EEG if seizures are suspected as cause of neurological deficits 2