Normal Fasting Blood Sugar

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A normal fasting blood sugar is a fasting plasma glucose below 100 mg/dL, the reference figure published by the American Diabetes Association and reproduced by the US National Institute of Diabetes and Digestive and Kidney Diseases (NIDDK). Fasting glucose is one of the commonly ordered blood sugar tests, and it is also a test where published guidelines visibly differ from one another. This page sets out what fasting means for the test, what the figures are, where the ADA and WHO part company, and why one result on its own settles nothing.

What fasting means for this test

Fasting means a set gap with no food and no calorie-containing drinks before the sample is taken. The NIDDK states that for the most reliable results the test is given in the morning after you have fasted for at least 8 hours. MedlinePlus describes the same preparation before a glucose tolerance test: nothing to eat or drink for at least 8 hours.

Two practical points follow. The overnight gap is what makes the result comparable to the published figures, so a sample taken a few hours after breakfast is a different test rather than a poor fasting test. And your laboratory may give its own instructions about water, timing and medicines. Follow the instructions your laboratory and your doctor give you, not a general rule from a web page.

If you take regular medicines, ask your doctor before changing anything in order to fast. Skipping or delaying a dose is a decision for the prescriber, never something to do on your own.

The published fasting figures

These are the fasting plasma glucose figures published by the American Diabetes Association and reproduced by the NIDDK, stated in mg/dL, the unit most Indian reports use.

• Reference range for adults who are not pregnant: less than 100 mg/dL. The ADA wording is normal less than 100 mg/dL; the NIDDK table expresses the same boundary as 99 mg/dL or below.
• Prediabetes, also called impaired fasting glucose: 100 to 125 mg/dL.
• Diabetes: 126 mg/dL or above.

These are diagnostic decision rules for clinicians, not personal targets, and they say nothing about how well or unwell any individual is. For how this test sits alongside the after-food and random tests, see normal blood sugar levels.

The ADA and WHO do not draw the same line

This is a real, published disagreement, and it is better to know about it than to meet it by accident.

• WHO, diabetes cut-off: a fasting value of 7.0 mmol/L (126 mg/dl) or above. This matches the ADA figure.
• WHO and IDF, impaired fasting glucose: 6.1 to 6.9 mmol/l inclusive, that is 110 to 125 mg/dl, with a two-hour plasma glucose, if measured, below 7.8 mmol/l (140 mg/dl).
• ADA, prediabetes: 100 to 125 mg/dL.
• NICE, United Kingdom: a fasting value of 5.5 to 6.9 mmol/l is treated as high risk of type 2 diabetes, below 5.5 mmol/l as moderate risk, and 7.0 mmol/l or above as possible type 2 diabetes requiring a second test.

So the three bodies agree on where diabetes begins and disagree on where the intermediate zone begins. A fasting result from 100 mg/dL up to just under 110 mg/dL falls inside the ADA prediabetes band but below the lower boundary WHO uses for impaired fasting glucose, while NICE would place it in a risk category rather than a diagnostic one. None of that changes the person. It changes the label, and which label appears depends on which guideline your laboratory and doctor follow.

mg/dL and mmol/L on the same report

Indian laboratory reports usually print glucose in mg/dL. WHO documents and UK guidance use mmol/L. They describe the same measurement in different units.

Rather than converting numbers in your head, use the paired values the guidelines themselves print. WHO gives its fasting diabetes cut-off as 7.0 mmol/L (126 mg/dl), and impaired fasting glucose as 6.1 to 6.9 mmol/l (110 to 125 mg/dl). If your report is in one unit and the guidance you are reading is in the other, ask the laboratory or your doctor to confirm rather than relying on arithmetic you are unsure of.

Why a second test matters

The NIDDK states that usually a doctor will use a second test to confirm diabetes. NICE takes the same approach, describing a fasting value of 7.0 mmol/l or above as indicating possible type 2 diabetes and requiring a second test.

Confirmation may repeat the same test or use a different one. HbA1c is often used alongside glucose testing, and for it the ADA gives a reference figure of below 5.7%, with 5.7% to 6.4% as prediabetes and 6.5% or higher as diabetes; WHO gives the same diabetes cut-off, written as 6.5% or 48 mmol/mol. If your doctor has asked for that test, it can be arranged as HbA1c testing at home in Bangalore.

Confirmation is not paperwork. Glucose genuinely varies from day to day, fasting is sometimes incomplete, an infection or a sleepless night can shift a value, and a diagnosis carries long-term consequences. It is worth being right.

What moves a fasting result, and reading your own report

• An incomplete fast, or a much longer fast than the laboratory expected
• Illness, infection, injury or severe stress
• Poor sleep, night-shift work, or hard exercise the day before
• Other medicines taken for other conditions
• Pregnancy, which is assessed with its own tests and thresholds
• Whether the sample was venous blood run in a laboratory or a finger-prick reading on a home meter. The WHO criteria are defined on venous plasma glucose

Reference ranges also vary by laboratory and by method, and with age, sex, pregnancy and the clinical situation. MedlinePlus states that normal value ranges may vary slightly among different labs. The range that applies to you is the one printed next to your result on your own report, and if it differs from the figures on this page, that printed range is what your doctor works from. This guide explains the test; your treating doctor interprets the result alongside your history and symptoms.

If getting to a laboratory early in the morning is hard, blood sugar testing at home in Bangalore can collect a fasting sample at home. For the other half of the picture, read blood sugar after eating.

A fasting number on its own is not an emergency reading, but some symptoms are. Call 108 or go to the nearest hospital straight away if someone is unresponsive or cannot be woken, is having a seizure, is confused and cannot swallow safely, or is vomiting repeatedly and breathing rapidly.

Frequently asked questions

Sources

NIDDK, NIH - Diabetes Tests and Diagnosis · American Diabetes Association - Diabetes Diagnosis and Tests · WHO - Classification of diabetes mellitus (2019) · WHO and IDF - Definition and diagnosis of diabetes mellitus and intermediate hyperglycaemia (2006) · NICE - Type 2 diabetes: prevention in people at high risk (PH38) · MedlinePlus, NIH - Glucose tolerance test (non-pregnant)

Last checked 2 September 2026. How we write and check these pages: editorial policy.