What labs should be ordered for an elderly patient presenting with confusion?

Laboratory Workup for Confusion in Elderly Patients

Order a finger-stick blood glucose immediately upon patient contact, followed by a comprehensive metabolic panel, complete blood count with differential, urinalysis, thyroid function tests, and vitamin B12 level as your core first-line laboratory evaluation. 1, 2

Immediate Priority Testing

• Check blood glucose first before any other testing, as hypoglycemia is rapidly reversible, can be fatal if missed, and frequently mimics intoxication or other causes of confusion 2, 3
• If glucose is low, administer 30-50 g IV glucose urgently 2

Core First-Line Laboratory Panel (Tier 1)

Complete Blood Count (CBC) with Differential 1, 2, 3

• Identifies infection, anemia, and hematologic abnormalities that commonly contribute to altered mental status
• Infection is a predominant cause in elderly patients admitted with confusion 4

Comprehensive Metabolic Panel 1, 2, 3

• Include electrolytes, renal function (BUN, creatinine), hepatic panel (AST, ALT, bilirubin, albumin), glucose, calcium, magnesium, and phosphate
• Metabolic disturbances are frequently reversible causes of confusion 5

Urinalysis 1, 2, 3

• Screen for urinary tract infections, which are especially common causes of confusion in elderly patients
• Urinary tract infections are among the most frequent precipitants of delirium in this population 3

Thyroid Function Tests (TSH, free T4) 1, 2, 3

• Thyroid dysfunction is a reversible cause of confusion
• Essential to rule out as part of standard dementia workup 6

Vitamin B12 Level 1, 2, 3

• Nutritional deficiencies can cause cognitive impairment
• B12 deficiency is a potentially reversible cause of dementia 5

Context-Specific Additional Testing

Toxicology Screen and Blood Alcohol Level 1, 2, 3

• Order if substance use is suspected based on history
• Medication review is crucial, as iatrogenic causes are more common in patients who develop confusion after hospitalization 4

Arterial Blood Gas 1, 2

• Order if respiratory concerns are present or hypoxemia is suspected
• Hypoxia from pulmonary embolism can present as acute confusion in elderly patients 7

Cardiac Enzymes and 12-Lead ECG 2, 3

• Order if myocardial ischemia is suspected
• Congestive heart failure is a predominant cause in elderly patients admitted with confusion 4

Inflammatory Markers (ESR, CRP) 1, 3

• Screen for inflammatory or infectious processes
• In patients over 50 with headache, scalp tenderness, or jaw claudication, order emergently to evaluate for giant cell arteritis 3

Pregnancy Test 2

• In women of childbearing age presenting with confusion

Selective Advanced Testing (Only When Clinically Indicated)

Lumbar Puncture with CSF Analysis 1, 2, 3

• Perform when fever is present without clear source, meningeal signs are present, or patient is immunocompromised
• Include opening pressure, cell count and differential, protein, glucose

Autoimmune Panels 1, 3

• Order ANA, ANCA if vasculitic process is suspected
• Consider antiphospholipid antibodies in younger patients or when no clear etiology is identified

HIV and RPR Testing 1

• Order if risk factors are present
• HIV infection is an irreversible cause of dementia 5

Thyroid Antibodies (TPO, Thyroglobulin) 1

• Consider for Hashimoto's encephalopathy when other causes excluded

What NOT to Order Routinely

Ammonia Levels 1, 2

• Do NOT routinely order in cirrhotic patients, as they are variable, unreliable, and elevated in non-hepatic encephalopathy conditions
• However, a low ammonia level in a confused patient points away from hepatic encephalopathy

Extensive "Shotgun" Panels 2

• Avoid reflexive extensive testing, as history and physical examination predict 83-98% of clinically significant abnormalities
• Routine broad testing yields only 1.4-1.8% clinically meaningful results not detected by history and physical

Brain Imaging Indications

Order CT or MRI Brain Selectively 1, 2, 3

• First episode of altered mental status
• Focal neurological deficits present
• Recent head trauma
• New-onset seizures
• Signs of increased intracranial pressure
• Unsatisfactory response to treatment of identified precipitating factors
• Do NOT order routinely for recurrent, non-focal presentations similar to prior episodes 2

Critical Pitfalls to Avoid

• Never assume intoxication without first ruling out hypoglycemia, as clinical presentations overlap significantly and hypoglycemia can cause permanent brain damage 2
• Do not delay glucose testing to obtain neuroimaging first 2
• Do not attribute symptoms to dementia without investigating for acute causes such as infections, medications, metabolic disturbances 1, 5
• Do not overlook medication-related causes, particularly in elderly patients where iatrogenic disease is common 1, 4
• Recognize that confusion is a diagnosis of exclusion and always investigate for reversible causes 2, 5
• Obtain collateral history from a knowledgeable informant to determine baseline cognitive function and characterize acute changes, as this is foundational to distinguishing delirium from dementia 3, 8

Clinical Context

The timing and collateral history are key to diagnosis 8. In elderly patients admitted with confusion, infection and congestive heart failure predominate, while iatrogenic disease is more common in those who develop confusion after hospitalization 4. A diagnosis of the cause can be made in the vast majority of cases with appropriate evaluation 4. All but the rarest causes of confusion can be identified based on complete history, medication review, physical examination, and the laboratory evaluation outlined above 5.