Not medically reviewed
Glucose
Fasting plasma glucose (FPG)
Not medically reviewed · Content last updated · 1 min read ·
This is the date the draft was written, not a medical review date.
Fasting plasma glucose is used to screen for and diagnose diabetes mellitus and intermediate hyperglycaemia (prediabetes).
Reference interval
| Conventional (mg/dL) | SI (mmol/L) | |
|---|---|---|
| Adults | 70–99 mg/dL | 3.9–5.5 mmol/L |
Specimen: Plasma (fluoride-oxalate tube) after at least 8 h fast · Conventional × 0.0555 = SI
Causes of high values
Diabetes mellitus (fasting 126 mg/dL / 7.0 mmol/L or above on repeated testing, per ADA and WHO), impaired fasting glucose (100-125 mg/dL by ADA; WHO uses 110-125), pancreatitis, Cushing syndrome, acromegaly, corticosteroids and acute stress.
Causes of low values
Hypoglycaemia (below about 70 mg/dL, 3.9 mmol/L): insulin or sulfonylurea excess, prolonged fasting, adrenal insufficiency, liver failure, insulinoma, alcohol and sepsis.
Pre-analytical and method notes
Unglycolysed samples lose about 5-7 % of glucose per hour at room temperature; use a fluoride tube or separate promptly. Diagnostic thresholds (7.0 mmol/L, 6.1 or 5.6 mmol/L lower cut-offs) differ between WHO and ADA and diagnosis requires confirmation in the absence of symptoms; follow local guidelines. Capillary meter values differ from laboratory plasma glucose.
References
- Standards of Care in Diabetes (annual publication in Diabetes Care). American Diabetes Association — Tier 2 (guidelines / primary literature)
- Definition and diagnosis of diabetes mellitus and intermediate hyperglycaemia: report of a WHO/IDF consultation. World Health Organization (2006) — Tier 1 (standards / international bodies)
- Rifai N, Horvath AR, Wittwer CT. Tietz Textbook of Clinical Chemistry and Molecular Diagnostics. Elsevier, 6th edition (2018) — Tier 3 (textbook)
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