Metabolic . Patient guide
Fasting Glucose
Also known as: Fasting Plasma Glucose, FPG
What is Fasting Glucose
Fasting glucose is the blood sugar level measured after an overnight fast. It is one of three accepted UK tests for diabetes diagnosis (alongside HbA1c and oral glucose tolerance test) and pairs naturally with HbA1c for a full metabolic snapshot.
This biomarker entry is being clinically reviewed by our team. The factual content draws on UK guidance (NICE, NHS, Royal Colleges and the relevant speciality society where cited).
Reference range
Reported in mmol/L (also seen as mg/dL (multiply mmol/L by 18)). Final reports always carry the issuing laboratory's range, which is what your clinician will interpret against.
| Group | Range | Note |
|---|---|---|
| Normal | under 5.6 | mmol/L |
| Impaired fasting glucose / non-diabetic hyperglycaemia | 5.6 to 6.9 | NICE PH38 uses 5.5 to 6.9 as the at-risk band |
| Diabetes range (confirmation required) | 7.0 and over |
What it is
Blood glucose rises after meals and falls between them, with insulin and counter-regulatory hormones holding it within a narrow range. After an 8 to 12 hour overnight fast the glucose level reflects the body's baseline regulation. Persistently raised fasting glucose indicates that insulin is no longer holding the baseline at normal level, the earliest measurable signal of type 2 diabetes.
Why a clinician would order it
Fasting glucose is checked in diabetes screening, pre-diabetes work-up, metabolic risk assessment, investigation of fatigue or unexplained weight gain, PCOS / PMOS work-up (where insulin resistance is common), and in patients with a family history of type 2 diabetes. Paired with HbA1c and fasting insulin it gives the most complete short-term + long-term picture of glucose handling.
If your level is outside the range
Symptoms of low Fasting Glucose
- Hypoglycaemic symptoms attributable to fasting glucose are rare in non-diabetic patients on a normal diet
- Mild light-headedness or hunger if fast is prolonged
What low can indicate. Excellent insulin sensitivity (typical in athletes), prolonged fasting, recent vigorous exercise, certain medications, or rarely insulinoma if extremely low without explanation.
Symptoms of high Fasting Glucose
- Often none in pre-diabetes (the silent stage)
- Excessive thirst (polydipsia)
- Frequent urination (polyuria)
- Fatigue
- Blurred vision
- Unexplained weight loss (later)
- Recurrent infections
What high can indicate. Pre-diabetes (commonest UK finding in the 5.6 to 6.9 range), type 2 diabetes (7.0+ requires confirmation), Cushing's syndrome, steroid use, acute stress response (recent illness or surgery raises glucose transiently), or rarely type 1 diabetes if very high in a younger patient.
Testing tips
Strict overnight fast (8 to 12 hours, water only). No coffee, no smoking, no exercise in the morning before the draw. Hold metformin and other glucose-lowering medications only on clinician advice. Always interpret alongside HbA1c (which reflects the previous 8 to 12 weeks rather than the moment of the draw) and fasting insulin (which catches insulin resistance years before glucose rises). A single raised fasting glucose needs a confirmatory repeat draw before a diabetes diagnosis is made.
Where you can get this tested
Fasting Glucose is included in the following WMG Health panels. Same-day appointments at our Harley Street clinic, with results clinician-reviewed.
Want a specific combination of markers we do not have a panel for? Build a custom panel and our clinicians will design one for you.
Symptoms often investigated with Fasting Glucose
Fasting Glucose is commonly tested when patients present with the following symptoms. If any of these resonate with you, the linked guides explain what to look for and which test pathway is appropriate.
Read this marker alongside another
Fasting Glucose is most useful when interpreted together with the markers below. Each guide walks through the 4-quadrant matrix our clinicians use when both come back at once.
Related markers
Sources
UK guidance our clinicians use when interpreting this marker.
This page is general patient information, not personal medical advice. A GMC-registered clinician will review your results and tailor any interpretation to you. See our Editorial Policy for how we write and review content.
Common questions about Fasting Glucose
What is a normal Fasting Glucose range?
Normal: under 5.6 (mmol/L). Impaired fasting glucose / non-diabetic hyperglycaemia: 5.6 to 6.9 (NICE PH38 uses 5.5 to 6.9 as the at-risk band). Diabetes range (confirmation required): 7.0 and over. Always interpret your own results against the laboratory range printed on your report, since assay-specific reference ranges vary.
What does a low Fasting Glucose result mean?
Excellent insulin sensitivity (typical in athletes), prolonged fasting, recent vigorous exercise, certain medications, or rarely insulinoma if extremely low without explanation.
What does a high Fasting Glucose result mean?
Pre-diabetes (commonest UK finding in the 5.6 to 6.9 range), type 2 diabetes (7.0+ requires confirmation), Cushing's syndrome, steroid use, acute stress response (recent illness or surgery raises glucose transiently), or rarely type 1 diabetes if very high in a younger patient.
Do I need to fast or prepare for the Fasting Glucose blood test?
Strict overnight fast (8 to 12 hours, water only). No coffee, no smoking, no exercise in the morning before the draw. Hold metformin and other glucose-lowering medications only on clinician advice. Always interpret alongside HbA1c (which reflects the previous 8 to 12 weeks rather than the moment of the draw) and fasting insulin (which catches insulin resistance years before glucose rises). A single raised fasting glucose needs a confirmatory repeat draw before a diabetes diagnosis is made.
Can I order a Fasting Glucose blood test privately in London?
Yes. WMG Health offers Fasting Glucose as part of bespoke panels and several pre-built panels at our 134 Harley Street clinic. Results are clinician-reviewed by a GMC-registered doctor within 4 hours for the most common assays. Bespoke panels from £180; bookings via /contact/ or 020 3239 3378.