📊 Blood Sugar Levels: What’s Normal, What’s Prediabetes, What’s Diabetes?

You’ve pricked your finger, the glucometer beeps, and a number appears. Is it good, bad, or somewhere in between? Understanding blood sugar ranges — for fasting, after meals, and random checks — is essential for anyone concerned about diabetes. Dr. Ravi Sishir Reddy explains the official cutoffs for normal, prediabetes, and diabetes, as well as the targets people with diabetes should aim for.

1. The Three Main Types of Blood Sugar Tests

• Fasting blood sugar (FBS): Measured after no caloric intake for at least 8 hours. It reflects how well the body maintains glucose overnight.
• Postprandial blood sugar (PPBS): Measured 2 hours after the start of a meal. It shows how the body handles a glucose load.
• Random blood sugar (RBS): Measured at any time of day, regardless of when you last ate. A very high random sugar with symptoms can diagnose diabetes, but it’s less precise for routine monitoring.

The HbA1c test, which reflects average glucose over 2‑3 months, is covered in a separate article.

👉 Read more: HbA1c Test Explained →

2. Blood Sugar Ranges: Normal, Prediabetes, and Diabetes

The table below summarises the diagnostic criteria used by the American Diabetes Association (ADA) and World Health Organization (WHO). Values are in mg/dL (multiply by 0.0555 to convert to mmol/L).

Test	Normal	Prediabetes	Diabetes
Fasting (FBS)	Below 100 mg/dL	100 – 125 mg/dL	126 mg/dL or higher
2‑Hour Postprandial (PPBS/OGTT)	Below 140 mg/dL	140 – 199 mg/dL	200 mg/dL or higher
Random (RBS)	Below 140 mg/dL (usually)	N/A (not diagnostic)	200 mg/dL + symptoms
HbA1c	Below 5.7%	5.7% – 6.4%	6.5% or higher

A single abnormal test should be confirmed on a second occasion, unless symptoms are unequivocal.

3. What Should Your Blood Sugar Be If You Already Have Diabetes?

Once diabetes is diagnosed, the goals shift from diagnosis to management. Dr. Reddy explains the commonly recommended targets, though these may be individualised based on age, duration of diabetes, and other health conditions:

• Fasting blood sugar: 80 – 130 mg/dL (4.4 – 7.2 mmol/L).
• Postprandial (2 hours after meal): Less than 180 mg/dL (10.0 mmol/L).
• HbA1c: Less than 7.0% for most adults; some guidelines suggest < 6.5% for younger, healthier patients, and < 8.0% for older, frail patients.

These are general targets. For example, pregnant women with diabetes have much stricter goals (fasting < 95 mg/dL, 1‑hour post‑meal < 140 mg/dL). Your doctor will set personalised targets.

4. Why Your Blood Sugar Fluctuates

Blood sugar is not a static number. It’s influenced by:

• Food: Carbohydrates have the most direct impact.
• Physical activity: Exercise lowers glucose by increasing muscle uptake.
• Stress and illness: Cortisol and adrenaline raise glucose.
• Medications: Insulin and sulfonylureas lower glucose; steroids raise it.
• Sleep: Poor sleep impairs insulin sensitivity.
• Dawn phenomenon: A natural rise in glucose in the early morning due to hormonal changes.

If you see an unexpected high or low reading, consider these factors before panicking. Consistent patterns are more important than a single outlier.

5. When Should You Check Your Blood Sugar?

For people without diabetes, an annual fasting glucose check (or as recommended by your doctor) is sufficient if you have risk factors. For those with prediabetes, every 3‑6 months may be needed to track progress. For people with diabetes, the frequency depends on treatment:

• On insulin: At least 2‑4 times daily (before meals and at bedtime), sometimes more.
• On oral medications: At least once daily, varying the time (fasting some days, post‑meal others) to get a full picture.
• On diet alone: A few times a week, or as directed by your doctor.

Continuous glucose monitors (CGMs) provide a more comprehensive view for those who need intensive monitoring.