What is the reference range for glucose levels in an adult patient with diabetes in the Emergency Room (ER) setting?

Emergency Room Glucose Reference Ranges

In the Emergency Room, there is no single "reference range" used for glucose levels in the traditional sense—instead, clinical decision-making is based on absolute treatment thresholds that apply regardless of fasting status, with critical values at <70 mg/dL for hypoglycemia and ≥180 mg/dL for initiating treatment of hyperglycemia. 1, 2

Understanding ER Glucose Interpretation

The ER does not use the same "normal reference ranges" that apply to outpatient screening or diagnosis. Instead, emergency physicians use action thresholds that trigger immediate clinical interventions:

Critical Low Threshold (Hypoglycemia)

• Glucose <70 mg/dL (3.9 mmol/L) is considered clinically important hypoglycemia requiring immediate treatment with 15-20 g of glucose 3
• Glucose <54 mg/dL (3.0 mmol/L) represents Level 2 hypoglycemia where neuroglycopenic symptoms begin and requires urgent action 3
• Level 3 hypoglycemia involves altered mental or physical status requiring assistance for treatment 3

Critical High Threshold (Hyperglycemia)

• Glucose ≥180 mg/dL persistently triggers initiation of insulin therapy in the ER and hospital setting 1, 2
• For hospitalized patients (including those admitted from the ER), the target glucose range is 140-180 mg/dL for most patients 1, 4, 2
• For non-critically ill hospitalized patients, premeal glucose target is <140 mg/dL and random glucose <180 mg/dL 3, 1

Why ERs Don't Use Traditional Reference Ranges

The key distinction is that ER glucose management is based on absolute values that apply immediately, regardless of when the patient last ate. 2 This differs fundamentally from outpatient screening criteria:

• Traditional "normal fasting glucose" of 70-110 mg/dL 5 or <100 mg/dL 6, 7 applies only to screening and diagnosis, not acute treatment decisions
• The ER cannot wait to determine fasting status before treating dangerous glucose levels 2
• Treatment thresholds of 180 mg/dL apply whether the patient is fasting or fed 2

Context-Specific Glucose Targets in the ER

For Critically Ill Patients

• Start IV insulin when glucose exceeds 180 mg/dL 1, 2
• Maintain glucose between 140-180 mg/dL once insulin is started 3, 1, 8
• More stringent targets of 110-140 mg/dL may be appropriate for select patients (e.g., cardiac surgery) if achievable without significant hypoglycemia 1, 2
• Avoid targets <110 mg/dL due to increased hypoglycemia risk and associated mortality 1, 2

For Non-Critically Ill Patients

• Premeal glucose target <140 mg/dL 3, 1
• Random glucose <180 mg/dL 3, 1

Common Pitfalls to Avoid

• Never delay treatment waiting to determine fasting status—the 180 mg/dL threshold applies immediately regardless of meal timing 2
• Don't confuse diagnostic criteria with treatment thresholds—outpatient screening values (fasting glucose 100-125 mg/dL for prediabetes) are not relevant to acute ER management 2, 6, 7
• Avoid overaggressive glucose lowering targeting <110 mg/dL, which increases hypoglycemia risk and mortality 1, 2
• Don't use sliding-scale insulin as sole therapy in the ER or hospital setting, as it is strongly discouraged and associated with poor outcomes 1, 2