If your blood sugar is too high, the most important first steps are to drink water, check for ketones if you’re above 250 mg/dL, and avoid exercise until you know it’s safe. Most mild spikes come down on their own or with your usual medication plan, but readings above 300 mg/dL or symptoms like vomiting and fruity-smelling breath need emergency care.
What counts as “too high” and what you should do about it depends on how high the number is, how long it’s been elevated, and whether your body is showing warning signs of a dangerous shift. Here’s how to sort through it.
Know Your Numbers
Blood sugar typically doesn’t cause noticeable symptoms until it climbs above 180 to 200 mg/dL. Below that range, you might not feel anything at all, even though the level is above your target. Once you cross that threshold, you may start noticing increased thirst, frequent urination, blurry vision, headaches, or fatigue.
These are the key thresholds to keep in mind:
- Above 180 mg/dL: Symptoms may begin. Drink water and recheck in an hour or two.
- Above 250 mg/dL: Check your urine for ketones every four to six hours. Contact your diabetes care provider for guidance if ketones are present, even in small amounts.
- Above 300 mg/dL and staying there: Go to the emergency room or call 911.
- Above 600 mg/dL: This is a medical emergency called hyperosmolar hyperglycemic state, most common in people with type 2 diabetes. It involves extreme dehydration and can cause confusion or loss of consciousness.
What to Do Right Now
Start with water. Dehydration makes high blood sugar worse, and your kidneys need fluid to flush excess glucose through urine. Drink steadily, not all at once. Avoid sugary drinks, juice, and regular soda.
If you take rapid-acting insulin, you may already have a correction dose prescribed by your provider. The general principle is that one unit of rapid-acting insulin lowers blood sugar by roughly 50 mg/dL, but individual sensitivity varies widely, from 15 to over 100 mg/dL per unit. Never guess at a correction dose if you haven’t been given one. Stacking insulin (taking more before the first dose has finished working) is a common cause of dangerous low blood sugar.
If you take oral diabetes medication and your blood sugar is unusually high, don’t double your dose. Instead, focus on hydration, movement (if your level allows it), and contacting your provider if the number doesn’t come down within a few hours.
Why Exercise Needs Caution
Walking or light activity can help lower a mild spike by helping your muscles pull glucose out of your bloodstream. But there’s a ceiling. If your blood sugar is above 270 mg/dL, exercise can actually make things worse.
At that level, your body may not have enough insulin circulating to let glucose into your cells. When you exercise in that state, your liver releases even more glucose, and your body may start breaking down fat for fuel instead, producing ketones. That’s a recipe for ketoacidosis. The Mayo Clinic recommends testing your urine for ketones before exercising at readings above 270 mg/dL. If ketones are present, skip the workout entirely and focus on bringing your sugar down first.
How to Check for Ketones
Ketone urine test strips are available at most pharmacies without a prescription. You urinate on the strip and compare the color change to the chart on the bottle. Results fall into a few categories:
- Negative or trace: Generally not a concern for most people, though even small amounts increase your risk of ketoacidosis if you have diabetes. Contact your provider for next steps.
- Moderate or large: This puts you at serious risk for ketoacidosis. Go to the nearest emergency room.
If you don’t have strips on hand and your blood sugar is above 250 mg/dL, pay close attention to how you feel. Nausea, vomiting, stomach pain, fast deep breathing, extreme fatigue, or a fruity smell on your breath are all signs that ketones may be building up.
When It Becomes an Emergency
Two dangerous conditions can develop from sustained high blood sugar, and they require different awareness depending on your type of diabetes.
Diabetic ketoacidosis (DKA) is more common in type 1 diabetes but can happen in type 2. Your body, unable to use glucose for energy, starts breaking down fat rapidly, flooding your blood with acids called ketones. Early symptoms include nausea, stomach pain, and increased urination. As it progresses, you may develop fast deep breathing, a flushed face, dry mouth, muscle aches, and vomiting you can’t control. The CDC advises calling 911 or going to the ER if your blood sugar stays at or above 300 mg/dL, your breath smells fruity, you can’t keep food or fluids down, or you’re having trouble breathing.
Hyperosmolar hyperglycemic state (HHS) tends to affect people with type 2 diabetes, often older adults. Blood sugar can climb past 600 mg/dL, sometimes reaching ten times the normal level. The hallmark is extreme dehydration with confusion, dry mouth, and weakness, but often without the ketone buildup seen in DKA. HHS develops more slowly, sometimes over days or weeks, which makes it easy to miss until it becomes critical.
Food Choices That Help Bring Sugar Down
You don’t need to eat to lower blood sugar (in fact, not eating anything for a while is perfectly fine if your reading is high). But when you do eat next, what you choose matters. Soluble fiber slows the absorption of sugar from your digestive tract. Good sources include oats, beans, apples, citrus fruits, and nuts.
Some simple swaps make a real difference over time. Brown rice, barley, or farro in place of white rice. Beans or cauliflower rice instead of potatoes. Oatmeal with fruit instead of bagels or pastries. These aren’t just long-term dietary strategies. Choosing high-fiber, lower-glycemic foods for your next meal after a spike helps prevent the rebound effect where blood sugar crashes and then shoots back up again.
Pairing carbohydrates with protein or healthy fat also blunts the glucose response. A handful of almonds with an apple hits your bloodstream more gradually than the apple alone.
Patterns Matter More Than Single Readings
A one-time spike after a big meal or a stressful day is common and usually resolves on its own. What deserves more attention is a pattern: frequent readings above your target range, morning numbers that are consistently elevated, or spikes that take hours to come back down.
If you’re seeing high blood sugar episodes regularly, that’s a signal to talk with your diabetes care provider about adjusting your management plan. That conversation might lead to changes in your medication, your meal timing, your activity level, or some combination. Illness, stress, poor sleep, and certain medications (like steroids) can all push blood sugar higher than usual, so tracking what’s happening alongside your readings gives your provider much more to work with than the numbers alone.
Keep a simple log of your readings, what you ate, how active you were, and how you felt. Even a few days of this data can reveal patterns that are invisible when you’re just checking numbers in the moment.