What is the first test to perform on a patient with altered mental status?

First Test for Altered Mental Status in the Emergency Department

Check the blood glucose level immediately—this is the single most critical first test for any patient presenting with altered mental status, as hypoglycemia is rapidly reversible and can be fatal if missed. 1

Why Glucose Testing Takes Priority

Immediate Life-Threatening and Reversible

• Hypoglycemia is one of the few causes of altered mental status that can cause irreversible brain injury or death within minutes if untreated, yet is completely reversible with immediate glucose administration. 1
• In septic patients with altered mental status, hypoglycemia has a specificity of 86% when altered mental state is present at admission and is independently associated with in-hospital mortality. 1
• Signs and symptoms of hypoglycemia—including altered mental status, agitation, combativeness, and diaphoresis—are frequently confused with intoxication or drug/alcohol withdrawal, making it easy to miss without testing. 1

Evidence from Multiple Guidelines

• The Intensive Care Medicine guidelines specifically recommend checking blood sugar levels in every patient with altered mental status, with particular emphasis on those with impaired mental state at admission. 1
• The American Academy of Pediatrics guidelines for correctional institutions mandate that individuals with diabetes exhibiting altered mental status, agitation, combativeness, and diaphoresis should have finger-stick blood glucose levels measured immediately. 1
• Multiple seizure and delirium guidelines identify hypoglycemia as one of the most frequently encountered metabolic abnormalities in altered mental status, though it is usually predicted by history and physical examination. 1

Clinical Context for This Patient

High-Risk Features Present

• This patient has multiple red flags for hypoglycemia: found down (suggesting possible collapse), diaphoretic, and disoriented. 1
• The disheveled appearance and being found in a ditch raise concern for malnutrition, alcoholism, or liver disease—all conditions associated with increased hypoglycemia risk. 1
• Diaphoresis is a classic autonomic symptom of hypoglycemia that should trigger immediate glucose testing. 1

Why Other Tests Are Secondary

• CT head without contrast is important for altered mental status but should follow glucose testing, as neuroimaging has a yield of only 7.4-11% in patients with AMS and no focal deficits, and cannot be performed as rapidly as a finger-stick glucose. 1
• ECG is reasonable but does not address immediately reversible causes with the same urgency as hypoglycemia. 2
• Serum alcohol level may explain the presentation but does not require immediate treatment in the same way hypoglycemia does, and alcohol intoxication can coexist with hypoglycemia. 1

Practical Algorithm

Step 1: Immediate Glucose Check (Within 1-2 Hours of Arrival)

• Perform finger-stick blood glucose immediately upon patient contact. 1
• If glucose <70 mg/dL (<4 mmol/L), administer 30-50 g of intravenous glucose urgently. 1
• If unable to check blood glucose and patient has impaired mental state, make a presumptive diagnosis of hypoglycemia and administer intravenous glucose empirically. 1

Step 2: Simultaneous Basic Assessment

• While obtaining glucose, perform rapid assessment for trauma, focal neurological deficits, and vital signs. 1
• The American College of Radiology notes that metabolic derangements including hypoglycemia, hyperglycemia, and hyponatremia are among the wide range of life-threatening precipitating factors for delirium. 1

Step 3: Subsequent Testing Based on Initial Results

• If glucose is normal and no obvious cause identified, proceed with CT head (especially given history of being found down, raising trauma concern). 1
• Laboratory testing including comprehensive metabolic panel, complete blood count, and urinalysis should be guided by clinical evaluation. 2

Critical Pitfalls to Avoid

• Never assume altered mental status is due to intoxication without first ruling out hypoglycemia—the clinical presentations overlap significantly. 1
• Do not delay glucose testing to obtain neuroimaging first—even brief periods of hypoglycemia can cause detrimental effects. 1
• In patients with suspected alcohol use (as suggested by being found in a ditch), remember that alcohol withdrawal seizures and hypoglycemia commonly coexist. 1
• The American College of Emergency Physicians found that in prospective studies of new-onset seizures with altered mental status, unsuspected hypoglycemia was discovered in 1-2 patients per 100-250 cases, emphasizing that history and physical examination alone are insufficient. 1