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Glucose & Diabetes

Glucose, Fasting

Normal range 70–99 mg/dL (3.9–5.5 mmol/L SI). Specimen: Serum or plasma (fasting).

Also known as: FBS, fasting blood sugar, FPG.

70–99 mg/dLCritical: read below

Reference range

Conventionalmg/dL
7099
SImmol/L
3.95.5
SpecimenSerum or plasma (fasting)
Conventional range70–99 mg/dL
SI range3.9–5.5 mmol/L
Conversion factor×0.0555 (conventional → SI)
Critical value< 50 or > 400 mg/dL
PanelGlucose & Diabetes

Convert any Glucose, Fasting result between units on the unit converter.

What is the normal range for Glucose, Fasting?

The standard teaching reference range for Glucose, Fasting is 70–99 mg/dL in conventional units, or 3.9–5.5 mmol/L in SI units. This value is measured in serum or plasma (fasting).

A commonly taught critical (panic) value is < 50 or > 400 mg/dL. Critical results are reported to the provider immediately under your facility's policy.

Source: Adult reference values compiled from Pagana & Pagana, Mosby's Diagnostic and Laboratory Test Reference, and Fischbach & Dunning, A Manual of Laboratory and Diagnostic Tests. Reference ranges vary by laboratory, method, age, sex, and population — always use the range printed on the actual result.

Above the range

Common causes of a high Glucose, Fasting

  • Diabetes mellitus
  • Stress or illness
  • Corticosteroids
  • Pancreatitis

Below the range

Common causes of a low Glucose, Fasting

  • Excess insulin or sulfonylureas
  • Prolonged fasting
  • Adrenal insufficiency
  • Insulinoma

At the bedside

Nursing considerations

  • ≥ 126 mg/dL fasting on two occasions supports a diabetes diagnosis.
  • Treat symptomatic hypoglycemia immediately, then recheck.

Study aid

Your notes on Glucose, Fasting

Same panel

More Glucose & Diabetes tests

C-Peptide0.8–3.1 ng/mLGlucose, Random< 140 (non-fasting) mg/dLHemoglobin A1c (HbA1c)4–5.6 %Oral Glucose Tolerance Test (2-hour)< 140 (normal) mg/dL