Is a blood sugar of 300 an emergency?

The number is not the deciding factor

Someone whose readings usually sit around 90 will feel dreadful at 300. Someone who has run high for years may feel unremarkable at the same number. The reading alone does not tell you how much trouble you are in.

What decides it is ketones and symptoms.

Go to emergency care now if any of these apply

• Vomiting, or being unable to keep fluids down
• Deep, rapid breathing, or breath that smells sweet or fruity, like acetone or pear drops
• Abdominal pain that will not settle
• Confusion, unusual drowsiness, or difficulty staying awake
• Moderate or large ketones on a urine or blood test
• Signs of severe dehydration — sunken eyes, no urine output, a racing pulse

These point to diabetic ketoacidosis or a hyperosmolar hyperglycemic state. Both are life-threatening and both are treatable; the deciding factor is usually how quickly someone gets help.

If none of those apply

Still treat 300 as urgent rather than routine:

1. Check ketones if you have the means and use insulin. This is the single most useful piece of information.
2. Drink water. Rehydration helps the kidneys clear excess glucose. Modest effect, no downside.
3. Take a correction dose only if one has been prescribed to you and you have been taught to use it. Follow your correction factor, and wait the full interval before re-dosing — stacking insulin is how people end up hypoglycemic hours later.
4. Do not exercise if ketones are present. Without enough insulin, working muscle cannot use glucose and the body produces more ketones instead.
5. Retest in one to two hours rather than intervening again.
6. Contact your care team today, even if it comes down.

Above 400

Above 400 mg/dL (22.2 mmol/L) usually warrants emergency assessment regardless of how you feel. At that level the risk of ketoacidosis or a hyperosmolar state is substantial, and dehydration is often more advanced than it feels.

The part people skip

Two consecutive readings above 300 is a pattern, not an incident. Even after it settles, that needs a conversation about why — illness, a missed or degraded dose, a new medication like a steroid, or a treatment plan that genuinely needs adjusting.