What laboratory tests can be ordered for an elderly patient presenting with confusion?

Laboratory Testing for Elderly Patients with Confusion

Order a comprehensive cognitive lab panel immediately, including point-of-care glucose, complete metabolic panel, complete blood count, TSH, vitamin B12, and urinalysis—these tests identify the most common reversible causes of confusion in elderly patients and should be obtained in virtually all cases. 1, 2, 3

Immediate Point-of-Care Testing

• Finger-stick blood glucose must be checked first upon patient contact, as hypoglycemia is rapidly reversible and can be fatal if missed, with signs frequently mimicking intoxication or other conditions 2, 3
• If glucose is low, administer 30-50 g IV glucose urgently 3
• Pulse oximetry should be obtained immediately to assess for hypoxia, which is a common precipitant of confusion 2

Core Laboratory Panel (Tier 1 - Order on All Patients)

Complete Metabolic Panel (Chem-20)

• Includes electrolytes (sodium, potassium, chloride, bicarbonate), renal function (BUN, creatinine), hepatic panel (AST, ALT, bilirubin, alkaline phosphatase), glucose, calcium, magnesium, and phosphate 1, 2, 3
• Hyponatremia, hypernatremia, and hypercalcemia are among the most common reversible metabolic causes of altered consciousness 2
• Renal and hepatic dysfunction can precipitate or worsen confusion 1

Complete Blood Count with Differential

• Identifies infection (elevated WBC), anemia (which commonly contributes to confusion), and hematologic abnormalities 1, 2, 3
• Anemia from gastrointestinal bleeding is a frequent cause of confusion in elderly patients 4

Thyroid Function

• TSH level is mandatory as thyroid dysfunction (both hypothyroidism and thyrotoxicosis) is a reversible cause of confusion and can present with new psychiatric symptoms in the elderly 1, 2, 3, 5

Vitamin B12 and Homocysteine

• Vitamin B12 deficiency causes neuropsychiatric symptoms and cognitive decompensation 1, 3
• Homocysteine should be included because hyperhomocysteinemia indicates functional B12 deficiency that may not be detected by B12 levels alone 1

Urinalysis

• Urinary tract infection is the most common infectious precipitant of confusion in elderly patients 1, 3
• Should be obtained routinely as part of the initial evaluation 1, 3

Context-Specific Additional Testing

When Infection is Suspected

• Chest X-ray if pulmonary infection is suspected (pneumonia is a common cause) 2, 3
• Blood cultures if sepsis is a concern 1

When Cardiac Etiology is Suspected

• 12-lead ECG in geriatric patients to evaluate for arrhythmias or myocardial ischemia 1, 3
• Cardiac troponin if myocardial ischemia is suspected 3
• Consider evaluation for syncope/orthostatic hypotension with orthostatic blood pressure measurements 1

When Substance Use is Suspected

• Toxicology screen and blood alcohol level 3
• Medication levels for drugs with narrow therapeutic windows (digoxin, anticonvulsants) 1

When Respiratory Concerns are Present

• Arterial blood gas analysis—hypoxia from pulmonary embolism can present as acute confusion and is often diagnosed late 6

In Women of Childbearing Age

• Pregnancy test 3

What NOT to Order Routinely

• Do not reflexively order extensive panels—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 clinical assessment 3
• Do not routinely order ammonia levels in cirrhotic patients, as they are variable, unreliable, and elevated in non-hepatic conditions; however, a low ammonia level points away from hepatic encephalopathy 3

When to Add Neuroimaging

Brain imaging (CT or MRI) should be ordered selectively, not routinely, with specific indications including: 2, 3

• First episode of altered mental status
• Focal neurological deficits
• Recent head trauma (especially in patients on anticoagulation) 2
• New-onset seizures
• Signs of increased intracranial pressure
• Unsatisfactory response to treatment of precipitating factors
• History of malignancy (concern for brain metastases) 2

Routine brain imaging is not necessary for recurrent, non-focal presentations similar to prior episodes, as the diagnostic yield is low (5-6.4%) in the absence of focal deficits or trauma 2, 3

Critical Pitfalls to Avoid

• Never assume intoxication without first ruling out hypoglycemia—clinical presentations overlap significantly and hypoglycemia can cause permanent brain damage 3
• Do not delay glucose testing to obtain neuroimaging first 3
• Dehydration is a common precipitating factor and should be assessed clinically and with laboratory markers 1, 4
• Review all medications for anticholinergic burden and deliriogenic agents (sedatives, benzodiazepines, antihistamines, tricyclic antidepressants)—polypharmacy is a major contributor to delirium 2, 7, 8
• Do not overlook infection—acute infectious diseases (UTI, pneumonia) are the most frequent causes of confusion in hospitalized elderly 4, 9
• Confusion is a diagnosis of exclusion—always investigate for reversible causes including infections, medications, metabolic disturbances, and substance withdrawal 3, 5

Special Considerations in Frail Elderly

• Patients with cognitive impairment, functional dependence, clinical severity, and polypharmacy are at highest risk for acute confusional states 4
• Cognitive status influences accuracy of recall—cognitive impairment is present in 5% of 65-year-olds and 20% of 80-year-olds 1
• Multiple risk factors are common in frail elderly (median of five risk factors), making risk-factor stratification more complex 1
• A diagnosis of confusion can be made in the vast majority of cases (22 of 24 in one study) with appropriate investigation 9