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Blood sugar explained

What fasting, one-hour, two-hour and HbA1c values mean, the WHO and ADA ranges in mmol/L and mg/dL, the signs of a hypo, and what a continuous monitor adds.

The readings

The shape, not just the points

Glucose is a curve. After a meal it rises for 45-75 minutes and falls back over the next two to three hours; the fasting value is the flat line between meals. What matters for how you feel is the shape — a tall spike that crashes to a hypo feels worse than a flat modest bump from the same calories, which is why protein, fibre and fat change a meal's effect without changing its energy.

Different readings answer different questions: the fasting value shows the overnight baseline, the two-hour value shows how well the body clears a meal, and HbA1c shows the three-month average. They can disagree — a normal fasting value with a diabetic two-hour value happens — which is why clinicians look at more than one.

Reference only, not a diagnosis: these are population-level WHO and ADA thresholds. Your own numbers get interpreted by a clinician against your history, medicines and other tests. Symptoms always outrank a number — a value that does not look alarming on a chart but comes with symptoms still deserves a phone call.

About the figures

Diagnostic thresholds follow the WHO definition and diagnosis of diabetes mellitus; treatment targets follow the ADA Standards of Care. Values are given in both mmol/L and mg/dL (conversion factor 18.018).

Sources: WHO — diabetes fact sheet · WHO — definition and diagnosis of diabetes mellitus and intermediate hyperglycaemia · ADA — Standards of Care in Diabetes · International Diabetes Federation — facts and figures · checked 2026-09-07