What is the most appropriate immediate investigation for a 29-year-old woman with known alcohol use disorder who presents with drowsiness, slurred speech, odor of alcohol, and stable vital signs?

Clinical Observation with Bedside Glucose Testing

The best next step is clinical observation with immediate bedside glucose measurement, not routine laboratory tests, urine drug screen, or neuroimaging. In this alert, cooperative patient with stable vital signs and a clinical presentation consistent with alcohol intoxication, extensive diagnostic testing provides minimal value and does not alter acute management 1.

Immediate Management Priority

Bedside capillary glucose must be checked immediately to exclude hypoglycemia, which is the most frequently missed life-threatening metabolic abnormality that mimics alcohol intoxication 1. This is the only mandatory test in this clinical scenario.

Why Routine Testing Is Not Indicated

Urine Drug Screen (Option A) - Not Recommended

• Routine urine toxicology screening does not change management in alert, cooperative patients with normal vital signs and a presentation consistent with alcohol intoxication 2
• Studies show that urine drug screens have only 20% sensitivity for detecting organic etiologies in psychiatric patients and do not influence disposition decisions 2
• Detection of marijuana metabolites (given her reported occasional cravings) can persist for weeks and would not alter acute management 1
• The American College of Emergency Physicians guidelines explicitly state that routine toxicologic screening is not supported by evidence in this population 2

Liver Function Tests (Option B) - Not Indicated Acutely

• LFTs are not indicated for acute evaluation of hemodynamically stable patients with isolated alcohol intoxication 1
• These tests are reserved for outpatient follow-up when signs of hepatic decompensation (jaundice, ascites, coagulopathy) are present 1
• While chronic alcohol use disorder increases risk of liver disease, LFTs do not address the acute presentation of slurred speech and drowsiness 1

TSH (Option C) - Not Indicated Acutely

• Thyroid function testing does not address the acute presentation and should be deferred to outpatient workup 1
• There is no clinical indication in this acute scenario that suggests thyroid dysfunction as the cause of her symptoms

Head CT (Option D) - Not Indicated Without Red Flags

• Non-contrast head CT is only warranted when focal neurologic deficits, trauma, markedly altered mental status beyond expected intoxication, or suspicion for structural brain lesions exist 1
• This patient has no focal deficits, no reported trauma, and her presentation is consistent with alcohol intoxication
• Routine neuroimaging in alert patients with normal vital signs and non-contributory examination has very low diagnostic yield 1

Appropriate Clinical Approach

After confirming normal glucose, the patient should be placed under clinical observation until she returns to baseline neurologic status 1. The key management principles include:

• Cognitive abilities, rather than a specific blood alcohol level, should guide psychiatric assessment 2
• Reassessment must verify that symptoms resolve in line with the expected timeline for alcohol metabolism 1
• An elevated blood alcohol concentration alone does not preclude psychiatric evaluation in alert, cooperative patients, but evaluation should await sufficient mental clarity 1

Triggers for Additional Workup

Further diagnostic testing should only be initiated if 1:

• Symptoms persist beyond the expected clearance period for alcohol
• New or worsening symptoms develop (focal deficits, seizures)
• Vital signs become abnormal
• Neurologic examination reveals unexpected findings

Disposition Planning

Given her known depression and alcohol use disorder, she should be referred for outpatient addiction treatment and mental health services as part of comprehensive care once medically stable 1. However, this addresses the underlying chronic conditions rather than the acute presentation.

The reflexive ordering of comprehensive "medical clearance" panels is discouraged; a focused assessment based on history, examination, and targeted testing (glucose only) is superior in stable intoxicated patients 1.