Hypoglycaemia

Video overview

This video walks through the key concepts covered on this page.

What glucose level counts as a hypo?

Physiologically, hypoglycaemia is a glucose level below 3.3 mmol/L (60 mg/dL). People without diabetes typically sit between 3.3 and 6.7 mmol/L (60 and 120 mg/dL) throughout the day.

In practice, 4.0 mmol/L (70 mg/dL) is the standard treatment threshold, and there is a good reason for this. In modern CGM accuracy studies, a reading in the low range is considered accurate if it falls within 0.8 mmol/L (15 mg/dL) of true blood glucose measured with lab-grade comparators such as YSI.

The mechanism: if true blood glucose is 3.2 mmol/L (58 mg/dL), a CGM can read up to approximately 0.8 mmol/L higher and still be labelled accurate. That puts the CGM display near 4.0 mmol/L (70 mg/dL). Setting the low alert and treatment threshold at 4.0 mmol/L therefore tends to catch almost all true hypos before they become physiologically dangerous.

If the alert were set at 3.3 mmol/L (60 mg/dL), a “safe” CGM error could mask a true glucose level of around 2.6 mmol/L (47 mg/dL) with no alarm. Many people find this is too narrow a margin.

Why pure glucose is the fastest treatment

Pure glucose starts raising blood glucose in about 10 minutes and has largely done its job by approximately 20 minutes. That is why the standard recheck point is 20 minutes, not 5 or 10.

Why body weight matters for dosing

Body weight is a rough proxy for blood volume and muscle mass. Larger bodies have more blood to fill with glucose and more tissue pulling glucose from the blood, especially after heavy bolus insulin or exercise. Treatment therefore tends to scale with weight.

This chart shows a simple weight-based guide:

Why cap treatment at approximately 18 to 20 grams? The intestine absorbs glucose at about 1 gram per minute. Taking more than roughly 20 grams and rechecking at 20 minutes tends to stack unabsorbed glucose in the gut, which often causes a delayed spike and sometimes gastrointestinal discomfort. A sensible first dose followed by a repeat if still low tends to produce cleaner results.

Why glucose tablets tend to work best

• Cheap, portable, and stable (they do not go off).
• Small, consistent doses (usually 3 to 4 grams per tablet), easy to split for precision.
• Treating a hypo is medicine, not a snack. “Tasty treats” tend to blur that line and can drive overeating loops.
• Liquid “glucose” drinks (Lucozade, Gatorade, and similar) are messy: formulations change, some use mixed sugars, they are bulky, hard to measure precisely, and often expensive.
• For faster swallowing, many people find that taking glucose tablets with water works well.

Using trend arrows for prevention

Treatment can differ depending on whether a hypo is already happening or is being prevented, and whether the CGM arrow is flat, single-down, or double-down. The full decision table lives in Dynamic Glucose Management, specifically the MATCH section of GAME-SET-MATCH.

Why sugar tends to overshoot

Sugar is slow. A sugar-based treatment can take up to an hour to fully correct a hypo. Many people re-treat too early, stack carbohydrate in the gut, then spike later.

The mechanism: sugar is glucose plus fructose. The glucose half helps quickly; the fructose half does not. It goes to the liver and can trigger hunger and overeating cascades (sometimes called the “overeating switch”). That is one reason sugar treatments so often end in rebound highs.

Are temporary basal reductions useful for hypos?

Temporary basal changes are the slowest mover of glucose. They tend to be too delayed to prevent or treat an imminent hypo. This is explored in more depth on the basal insulin page.