Why does the emergency department use a reference interval of 60–100 mg/dL for plasma glucose, and is a value of 100 mg/dL considered normal?

Why the ER Used a 60-100 mg/dL Reference Range

The emergency department used the 60-100 mg/dL reference range because this is the established pediatric reference interval for fasting plasma glucose, and many laboratories apply this same range universally or may have used it if you were younger, though the adult reference interval is actually 74-110 mg/dL. 1

Understanding Reference Intervals vs. Diagnostic Criteria

Reference intervals are NOT the same as diagnostic criteria for diabetes, and this is a critical distinction that causes confusion. 1

• Reference intervals represent the range of glucose values found in 95% of healthy individuals in a reference population 1
• The pediatric reference interval is 60-100 mg/dL (3.3-5.6 mmol/L) 1
• The adult reference interval is 74-110 mg/dL (4.1-6.1 mmol/L) 1
• However, diagnostic criteria for diabetes use completely different thresholds: normal fasting glucose is defined as <100 mg/dL by the American Diabetes Association 2, 3

Your Result of 100 mg/dL

Your value of 100 mg/dL sits at the upper limit of the pediatric reference range but is considered the threshold between normal and impaired fasting glucose by current diagnostic standards. 2, 3

• According to the American Diabetes Association, fasting plasma glucose <100 mg/dL is normal 2, 3
• Values of 100-125 mg/dL define impaired fasting glucose (prediabetes) 1, 2
• Values ≥126 mg/dL on two separate occasions indicate diabetes 1, 2

Your result of exactly 100 mg/dL technically falls into the impaired fasting glucose category, though it's at the very lowest end of this range. 2, 3

Why This Matters Clinically

The narrow gap between the reference interval upper limit and diagnostic thresholds creates potential for misinterpretation. 1

• The 97.5th percentile of fasting glucose in healthy populations is approximately 6.4 mmol/L (115 mg/dL), which is well above the 100 mg/dL threshold used for diagnosis 4
• Biological variation in fasting glucose ranges from 4.8-6.1% within the same person on different days 1
• For a true fasting glucose of 100 mg/dL, normal biological variation means repeat values could range from 87-113 mg/dL 1, 3

Important Caveats

Several factors could affect whether your 100 mg/dL result represents your true fasting glucose: 3

• Was the sample truly fasting (at least 8 hours without caloric intake)? 2, 3
• Stress and acute illness in the ER setting can elevate glucose levels 3
• Point-of-care glucose meters are less accurate than laboratory analyzers 1, 3
• Any abnormal result should be confirmed with repeat testing on a different day before making clinical decisions 1, 3

What You Should Know

Even values in the "high-normal" range (87-99 mg/dL) carry increased risk for future diabetes compared to lower values. 5, 6, 7

• Men with fasting glucose 87-99 mg/dL have progressively increased risk of developing type 2 diabetes compared to those with levels <81 mg/dL 5
• The risk of future diabetes increases in a non-linear fashion starting around 84 mg/dL 6
• If you have additional risk factors (obesity, family history, elevated triglycerides), your risk is substantially higher even at 100 mg/dL 5

The laboratory likely used the 60-100 mg/dL range as a general reference interval, but for clinical decision-making about diabetes risk, the American Diabetes Association criteria (<100 mg/dL = normal) are what matter most. 2, 3