What laboratory tests are recommended for an elderly patient presenting with confusion?

Laboratory Testing for Confused Elderly Patients

Order a focused cognitive lab panel immediately: fingerstick glucose, complete blood count (CBC), comprehensive metabolic panel (CMP), thyroid-stimulating hormone (TSH), vitamin B12, and urinalysis with culture. 1, 2

Immediate Point-of-Care Testing

• Fingerstick glucose must be performed first upon patient contact, as hypoglycemia is rapidly reversible and can be fatal if missed, with signs frequently confused with intoxication or other causes of confusion. 1
• If glucose is low, administer 30-50 g IV glucose urgently. 1
• Never assume intoxication without first ruling out hypoglycemia, as clinical presentations overlap significantly and hypoglycemia can cause permanent brain damage. 1

Core Laboratory Panel (Tier 1)

The following tests should be obtained in all or almost all confused elderly patients due to their low cost, wide availability, and acceptable yield for detecting common reversible causes: 3

Complete Blood Count (CBC) with Differential

• Identifies infection, anemia, and hematologic abnormalities that commonly contribute to altered mental status in elderly patients. 1, 2
• Infection is a leading cause of delirium, with urinary tract infections and pneumonia being the most frequent precipitants. 3, 4

Comprehensive Metabolic Panel (CMP)

• Detects electrolyte disturbances (particularly sodium and calcium), renal failure, hepatic dysfunction, and glucose abnormalities. 1, 2
• Electrolyte abnormalities are found in 6% of elderly patients with mental status changes. 2
• Include assessment of BUN, creatinine, glucose, calcium, magnesium, and phosphate. 1

Thyroid-Stimulating Hormone (TSH)

• Screens for thyroid dysfunction, a common and reversible cause of confusion in older adults. 3, 1, 2
• Thyroid dysfunction is newly diagnosed in 3% and exacerbated in 6% of elderly patients with mental status changes. 2

Vitamin B12 Level

• Identifies B12 deficiency, which can cause neuropsychiatric symptoms and cognitive impairment. 3, 1, 2
• Consider adding homocysteine level, as hyperhomocysteinemia is associated with functional B12 deficiency that may not always be detected by B12 levels alone. 3

Urinalysis with Culture

• Detects urinary tract infection, the most frequent precipitating infection in elderly patients with delirium. 4, 2
• Bacteriuria is found in 13% of elderly patients presenting with mental status changes. 2

Context-Specific Additional Testing

When Substance Use is Suspected

• Urine toxicology screen and blood alcohol level should be obtained, as 30% of psychiatric presentations may have toxicologic etiologies. 1, 2

When Cardiac Ischemia is Suspected

• Order cardiac enzymes (troponin) and 12-lead ECG. 1

When Respiratory Concerns are Present

• Obtain arterial blood gas, as hypoxia from pulmonary embolism can present as acute confusion. 1, 5

For Women of Childbearing Age

• Pregnancy test should be obtained. 1

When Infection Without Clear Source is Present

• Consider chest X-ray if pulmonary infection is suspected. 1, 2

What NOT to Order Routinely

• Do not routinely order ammonia levels in cirrhotic patients, as they are variable, unreliable, and elevated in non-hepatic encephalopathy conditions. 1, 4
• Avoid reflexive extensive panels, as history and physical examination predict 83-98% of clinically significant abnormalities, and routine testing yields only 1.4-1.8% clinically meaningful results not detected by history and physical. 1
• History has 94% sensitivity for identifying medical conditions causing psychiatric symptoms, while laboratory studies alone have only 20% sensitivity. 2

When to Add Brain Imaging

Brain imaging (CT or MRI) should be ordered selectively, not routinely, with specific indications: 1, 6

• First episode of altered mental status
• Focal neurological deficits on examination (93% of positive CT findings had new neurological findings) 6
• Recent head trauma or history of fall
• New-onset seizures
• Signs of increased intracranial pressure
• Significantly elevated blood pressure
• Lower Glasgow Coma Scale
• Unsatisfactory response to treatment of precipitating factors 1, 4

Do not order routine brain imaging for recurrent, non-focal presentations similar to prior episodes. 1

Critical Clinical Approach

• Assume delirium until proven otherwise, as it is often reversible with treatment of the underlying disorder. 7
• Distinguish delirium from dementia by time course: delirium develops over hours to days with fluctuating symptoms, while dementia progresses over months to years. 4
• Use the Confusion Assessment Method (CAM) to objectively diagnose delirium, which requires: (1) acute onset with fluctuating course, (2) inattention, and either (3) disorganized thinking or (4) altered level of consciousness. 4
• Do not miss hypoactive delirium, which is frequently mistaken for depression or fatigue and presents with cognitive and motor slowing rather than agitation. 3

Common Pitfalls to Avoid

• Never attribute acute confusion to pre-existing dementia without investigating reversible causes, as delirium commonly occurs superimposed on dementia. 4
• Do not delay glucose testing to obtain neuroimaging first. 1
• Always perform medication reconciliation, as polypharmacy is a major contributor to delirium in elderly patients, with benzodiazepines, neuroleptics, and opioids being common precipitants. 4
• Confusion is a diagnosis of exclusion—always investigate for reversible causes including infections, medications, metabolic disturbances, and substance withdrawal. 1
• Approximately 20% of acute psychosis cases have medical etiologies, with elderly patients at particularly high risk for organic causes. 2