BloodGlucoseValueUnderstand every reading

Blood glucose 4 — mmol/L or mg/dL?

72mg/dL4.0 mmol/L

Most meters outside the US show mmol/L. A reading of 4 is far more likely to be 4 mmol/L than 4 mg/dL.

If it is 4 mmol/L

= 72 mg/dL. Fasting without diabetes: Normal · With diabetes before a meal: Below target

Full explanation for 72 mg/dL →

If it really is 4 mg/dL

That is 0.2 mmol/L — severely low. Most meters show "LO" below 20 mg/dL. If the person is shaky, sweaty, confused or drowsy, treat it as a severe low: 15–20 g of fast sugar if they can swallow safely; if not, glucagon if available, recovery position and call 911 (US) or your local emergency number.

No immediate action needed

  • Note the time and whether you had eaten — the same number means different things fasting and after a meal.
  • Looking at the pattern over days (or a CGM report) tells you more than one reading.

If you don't have diabetes — reading 4 mmol/L (72 mg/dL)

72 mg/dL is a normal blood sugar both fasting and after a meal. Nothing to do.

Fasting (8+ hours without food)

NormalScale with 72 mg/dL marked5510012672 mg/dL

2 hours after eating (or glucose tolerance test)

NormalScale with 72 mg/dL marked5514020072 mg/dL

If you have diabetes — reading 4 mmol/L (72 mg/dL)

72 mg/dL is not a low, but it is below the usual pre-meal target of 80–130 mg/dL. If you use insulin or a sulfonylurea and are about to drive or exercise, have a small snack first.

Before a meal / fasting

Below targetScale with 72 mg/dL marked548013118124130072 mg/dL

1–2 hours after a meal

In targetScale with 72 mg/dL marked5418024130072 mg/dL

Targets for most non-pregnant adults (American Diabetes Association (ADA) Standards of Care). Your own targets may be different — for example in pregnancy, for children, older adults or people prone to lows. See pregnancy targets.

72 mg/dL as an average: HbA1c 4.1%

If 72 mg/dL were your average glucose over two to three months, it would match an HbA1c of about 4.1% (normal range). A single reading says little about your HbA1c — it is the long-term average that counts. Learn more in how to measure blood sugar.

Make sure the number is right

  • Wash and dry your hands before a finger-stick: fruit juice or sugar on the skin can raise the result a lot.
  • Home meters may differ from a lab value by up to about 15%. At 72 mg/dL that means roughly 61–83 mg/dL.
  • CGM sensors measure tissue fluid and lag 5–15 minutes behind blood when glucose changes quickly — confirm lows with a finger-stick.

Check another reading

Nearby values

This page explains one reading in general terms. It is not a diagnosis or a treatment instruction. Follow the plan agreed with your doctor or diabetes team.