If your blood sugar is high, the most important first steps are drinking water, checking for ketones if you’re above 240 mg/dL, and taking your prescribed insulin if you have a correction dose. How urgently you need to act depends on how high the number is and what symptoms you’re experiencing. A reading above 180 mg/dL two hours after eating is considered high, while anything above 300 mg/dL that won’t come down is a medical emergency.
Know Your Numbers and Thresholds
Normal blood sugar targets for most adults with diabetes are 80 to 130 mg/dL before a meal and under 180 mg/dL two hours after eating. When your reading climbs above those ranges, you’re in hyperglycemia territory. An occasional spike into the 200s can usually be managed at home. But certain thresholds call for specific actions:
- Above 240 mg/dL: Check your urine or blood for ketones using an over-the-counter test kit, especially if you feel sick.
- Above 270 mg/dL: Do not exercise. Physical activity at this level can push blood sugar higher rather than lower it.
- Above 300 mg/dL that stays elevated: This is emergency territory. Call 911 or go to the ER.
- Above 600 mg/dL: This signals a life-threatening condition called hyperosmolar hyperglycemic state, which can cause confusion, hallucinations, loss of consciousness, and weakness or paralysis on one side of the body.
Immediate Steps to Lower a Spike
Start drinking water. Dehydration makes high blood sugar worse because your kidneys need fluid to flush excess glucose through urine. Aim for a glass every 15 to 30 minutes until your reading starts dropping. Avoid sugary drinks, juice, and regular soda, which will push your levels higher.
If you take rapid-acting insulin and your doctor has given you a correction factor or sliding scale, use it. Your correction factor tells you how much one unit of insulin will lower your blood sugar, and it’s different for everyone. Don’t stack doses on top of each other. After taking a correction dose, wait at least two to three hours before retesting and taking more insulin, since rapid-acting insulin needs that time to reach its full effect.
If you don’t use insulin, or you’ve already taken your medication and your sugar is still climbing, focus on hydration and avoid eating anything with carbohydrates until your numbers start to come down.
Why Exercise Helps, and When It Doesn’t
Light physical activity like a 15-minute walk can help lower blood sugar by making your muscles pull glucose out of your bloodstream for energy. For a moderate spike in the 180 to 250 range, a short walk is one of the most effective things you can do.
But if your blood sugar is above 270 mg/dL, exercise becomes risky. At that level, your body may not have enough insulin circulating to let your muscles use glucose properly. Instead of burning sugar for fuel, your body starts breaking down fat, which produces ketones. Exercise in this state can accelerate ketone production and trigger a dangerous condition called diabetic ketoacidosis (DKA). Before exercising with a reading above 270, test your urine for ketones. If ketones are present, skip the workout entirely and focus on bringing your sugar down first.
What to Eat (and Avoid) During a Spike
If you’re hungry during a high blood sugar episode, choose foods that won’t add to the problem. High-fiber, low-carb options are your best bet. Soluble fiber dissolves in water and forms a gel-like substance in your stomach that slows digestion and prevents further blood sugar spikes. Good choices include vegetables, nuts, seeds, and small portions of beans or lentils.
Avoid white bread, rice, pasta, cereal, fruit juice, and anything with added sugar. Even foods that seem healthy, like a banana or a bowl of oatmeal, deliver a significant carbohydrate load that your body can’t handle well when it’s already running high. Most adults should aim for 22 to 34 grams of fiber per day as a general habit, which helps smooth out blood sugar over time.
Non-Food Triggers That Raise Blood Sugar
High blood sugar doesn’t always come from what you ate. Stress is one of the most common hidden triggers. When you’re under physical or emotional stress, your body releases adrenaline and cortisol, which signal your liver to dump stored glucose into your bloodstream. At the same time, those hormones make your cells less responsive to insulin. The result is a blood sugar spike that can seem to come out of nowhere.
Illness and infection work through the same mechanism, which is why blood sugar is notoriously hard to control when you’re sick. Dehydration, poor sleep, skipped medications, and even the “dawn phenomenon” (a natural hormone surge in the early morning hours) can all push your numbers up. If you’re seeing unexplained highs repeatedly, tracking patterns alongside your meals, sleep, stress levels, and medication timing can help you and your care team identify what’s going on.
When High Blood Sugar Is an Emergency
Two dangerous complications can develop from sustained high blood sugar: diabetic ketoacidosis and hyperosmolar hyperglycemic state. DKA is more common in type 1 diabetes but can happen in type 2. It develops when your body has so little usable insulin that it starts breaking down fat for energy at a dangerous rate, flooding your blood with acidic ketones.
The CDC recommends calling 911 or going to the emergency room if any of the following apply:
- Your blood sugar stays at 300 mg/dL or above despite correction efforts
- Your breath smells fruity
- You are vomiting and cannot keep food or fluids down
- You are having trouble breathing
- A ketone test shows high ketones
Hyperosmolar hyperglycemic state typically develops more slowly, over days to weeks, and is more common in older adults with type 2 diabetes. Blood sugar climbs above 600 mg/dL, and severe dehydration leads to confusion, delirium, or loss of consciousness. Both conditions are treated in the hospital with IV fluids and insulin, and both can be fatal without treatment.
Preventing the Next Spike
Repeated high readings are a signal that something in your management plan needs adjusting. A few strategies that consistently help:
- Pair carbs with fiber, fat, or protein. Eating a piece of bread alone spikes blood sugar faster than eating it with avocado or cheese, because the fat and fiber slow digestion.
- Move after meals. Even a 10-minute walk after eating can blunt a post-meal spike significantly.
- Stay hydrated throughout the day. Chronic mild dehydration concentrates glucose in your blood.
- Check your sugar more often, not less. If you’re only testing fasting glucose, you’re missing post-meal spikes that could be driving your A1C up.
- Manage stress deliberately. Deep breathing, short walks, and consistent sleep aren’t just lifestyle advice. They directly reduce the hormones that raise blood sugar.
If you’re doing everything right and still seeing frequent highs, your medication or insulin dose may need adjustment. Blood sugar management is not static. It shifts with weight changes, aging, activity levels, and even seasons.