When should I go to the ER for high blood sugar?

Go to emergency care now

Any one of these alongside a high reading:

• Repeated vomiting, or being unable to keep fluids down
• Deep, rapid breathing — slow, laboured, sighing breaths (Kussmaul breathing)
• Breath that smells sweet or fruity, like acetone or pear drops
• Abdominal pain that will not settle
• Confusion, extreme drowsiness, or difficulty staying awake
• Moderate or large ketones on a urine or blood test
• Signs of severe dehydration — sunken eyes, no urine output for many hours, a racing pulse
• Any reading above 400 mg/dL (22.2 mmol/L)

These point to diabetic ketoacidosis or a hyperosmolar hyperglycemic state. Both are life-threatening and both are very treatable — the deciding factor is nearly always how quickly someone gets seen.

Call your care team today (not the ER, but not tomorrow)

• Above 240 mg/dL (13.3 mmol/L) with trace or small ketones
• Two consecutive readings above 300 mg/dL (16.7 mmol/L)
• Readings that will not come down despite a correction dose
• Any illness with vomiting or diarrhea while you have diabetes
• A high reading that you cannot explain and that has lasted more than a day

Do not wait to see if it settles

The most common reason people arrive at hospital seriously unwell with ketoacidosis is not that they ignored the numbers — it is that they were waiting for the correction to work while the underlying problem, usually an infection or a failed insulin supply, kept getting worse.

DKA develops over hours to a day. A hyperosmolar state develops over days and is more common in older adults with type 2 diabetes, where glucose can climb above 600 mg/dL with profound dehydration.

Two things not to do

Do not exercise if you are above 240 mg/dL with ketones present. Without enough insulin, working muscle cannot use glucose and the body produces more ketones instead — exercise makes it worse.

Do not stop taking insulin because you are not eating. During illness, insulin needs usually rise even when appetite falls. Stopping is one of the most common precipitants of DKA.

Worth doing before you need it

Ask your care team for your specific sick-day rules and thresholds, and write them down somewhere you will find them at 3am. Know whether you have ketone strips and whether they are in date.