Is the fasting blood glucose reference range applicable in acute emergency room settings?

Reference Ranges in Emergency Department Settings

No, the ER was not correct to use a fasting blood glucose reference range in the acute care setting—fasting status is irrelevant for glucose management in emergency and acute care environments, where treatment thresholds and target ranges are based on absolute glucose values regardless of fasting state. 1, 2

Why Fasting Reference Ranges Don't Apply in Acute Care

The fundamental issue is that acute care glucose management operates on entirely different principles than outpatient diabetes screening:

• Emergency departments and hospitals use absolute glucose thresholds for treatment decisions, not fasting-dependent reference ranges. The American Diabetes Association recommends initiating insulin therapy when glucose levels are persistently ≥180 mg/dL, with target ranges of 140-180 mg/dL for most hospitalized patients, regardless of whether the patient is fasting or fed. 1, 2

• Fasting status does not change the treatment threshold of 180 mg/dL. Whether a patient last ate 30 minutes ago or 12 hours ago, the same glucose targets apply in acute care settings. 1, 3

• For critically ill patients requiring invasive monitoring, blood glucose should be maintained between 140-180 mg/dL once IV insulin is started, with no distinction made for fasting versus non-fasting states. 1

The Acute Care Treatment Algorithm

The approach in emergency and hospital settings follows this structure:

For patients requiring emergency evaluation:

• Blood glucose ≥180 mg/dL with symptoms (vomiting, dehydration, altered mental status) requires immediate ED evaluation. 2
• Persistent glucose >250 mg/dL over 2 consecutive days warrants urgent medical attention regardless of symptoms. 2
• Any symptomatic hyperglycemia or glucose too high to measure requires immediate evaluation. 2

For hospitalized patients:

• Insulin therapy begins at glucose ≥180 mg/dL persistently. 1, 2
• Target range is 140-180 mg/dL for most patients. 1, 3
• More stringent goals of 110-140 mg/dL may be appropriate for select patients (such as cardiac surgery patients) if achievable without significant hypoglycemia. 1
• Targets <110 mg/dL should be avoided due to increased hypoglycemia risk and associated mortality. 1

For critically ill patients:

• IV insulin infusion starts at glucose >180 mg/dL. 1
• Maintain glucose between 140-180 mg/dL. 1
• Use validated written or computerized protocols for IV insulin administration. 1

Why This Matters Clinically

The distinction between fasting and non-fasting glucose is diagnostically relevant for diabetes screening in outpatient settings, but therapeutically irrelevant in acute care. 2, 3

• In acute illness, stress hyperglycemia, infection, medications (especially corticosteroids), and critical illness all elevate glucose independent of fasting status. 4, 5
• Newly discovered hyperglycemia in hospitalized patients (without prior diabetes diagnosis) is associated with 16% in-hospital mortality compared to 3% in known diabetics and 1.7% in normoglycemic patients—this risk exists regardless of fasting state. 5
• The physiologic stress of acute illness overrides normal fasting/fed glucose regulation, making fasting reference ranges meaningless. 5

Measurement Considerations in Acute Settings

The consensus guidelines focus on measurement accuracy and site of sampling, not fasting status:

• For critically ill patients with arterial or central venous catheters, blood samples should be drawn from the arterial line first, or venous line second, and analyzed via blood gas analyzer or central laboratory. 4
• Capillary (fingerstick) samples are only acceptable for patients whose severity of illness does not justify invasive vascular monitoring. 4
• Point-of-care glucometers must meet accuracy standards of 98% of readings within 12.5% of reference standard for critically ill patients. 4

Common Pitfalls to Avoid

• Never delay treatment waiting to determine fasting status. The 180 mg/dL threshold applies immediately regardless of when the patient last ate. 1, 2
• Don't use outpatient diagnostic criteria (fasting glucose ≥126 mg/dL for diabetes diagnosis) as treatment thresholds in acute care. These are screening tools, not treatment targets. 2
• 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—it is strongly discouraged and associated with poor outcomes. 1

The ER's use of a fasting reference range represents a fundamental misunderstanding of acute care glucose management principles, where absolute glucose values drive treatment decisions independent of nutritional state.