If your blood sugar is high, the first steps are to drink water, check for ketones if your reading is above 250 mg/dL, and take your prescribed medication if you have one. How urgently you need to act depends on how high the number is and what symptoms you’re experiencing. A reading in the 200s calls for calm, deliberate action. A reading above 400 with symptoms like vomiting or confusion is an emergency.
First Steps When Your Reading Is High
Start drinking water immediately. When blood sugar is elevated, your kidneys work harder to filter out the excess glucose through urine, which pulls water from your body. Staying hydrated supports that process and helps prevent dehydration, which can make hyperglycemia worse. Aim for steady sips rather than chugging a large amount at once.
If you take insulin or another glucose-lowering medication, follow the instructions your provider has given you for correction doses. For people on rapid-acting insulin, a general rule of thumb is that one unit lowers blood sugar by about 50 mg/dL, though your personal sensitivity could range anywhere from 15 to 100 mg/dL per unit. Your provider should have given you a specific correction factor. If you don’t have clear instructions for what to do when your sugar runs high, that’s a conversation worth having at your next appointment.
One important caution: don’t overcorrect. Bringing blood sugar down too aggressively can swing it too far in the other direction, causing low blood sugar, which creates a new set of problems. Lowering glucose takes time, and stacking corrections before the first one has fully kicked in is a common mistake.
When Exercise Helps and When It Doesn’t
Light movement, like a 15- to 20-minute walk after a meal, is one of the most effective ways to bring down a post-meal blood sugar spike. Your muscles pull glucose from the bloodstream for energy when they’re active, which lowers your levels without medication. Even something as simple as parking farther away from a restaurant and walking after eating can make a noticeable difference.
There’s a hard limit, though. 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 available to move glucose into your cells. Instead of burning sugar for fuel, your body starts breaking down fat, producing waste products called ketones. Exercising in that state raises your risk of a dangerous condition called ketoacidosis. Before working out with a reading that high, test your urine for ketones first. If ketones are present, skip the exercise and focus on hydration and medication instead.
Know Your Ketone Testing Threshold
The American Diabetes Association recommends checking for ketones any time your blood sugar is above 200 mg/dL. You can test with urine strips available at most pharmacies. Ketones in your urine mean your body is running low on insulin and is burning fat for energy in a way that produces acid. Small amounts of ketones can usually be managed at home with fluids and insulin (if prescribed), but moderate to large amounts need medical attention right away.
This is especially important for people with type 1 diabetes, who are more prone to ketoacidosis. But anyone with diabetes who sees persistently high readings should keep ketone strips on hand.
Emergency Warning Signs
Most high blood sugar episodes are uncomfortable but manageable. Some are genuinely dangerous. Call 911 or go to the emergency room if you notice any of these:
- Fruity-smelling breath: a hallmark sign that ketone levels are dangerously high
- Persistent vomiting: especially if you can’t keep food or liquids down
- Confusion or difficulty speaking: signs that your brain isn’t getting what it needs
- A reading above 600 mg/dL: the threshold for a life-threatening condition that can lead to seizures or coma
For people with type 1 diabetes, the main emergency risk is diabetic ketoacidosis, where acid builds up in the blood. For people with type 2 diabetes, extremely high readings (above 600 mg/dL) can trigger a different emergency called hyperosmolar hyperglycemic syndrome. This tends to develop more slowly, often over days or weeks, and is more common in older adults, people who are bedbound, or those who’ve run out of medication. Early symptoms include extreme thirst, dry mouth, weakness, and frequent urination. Left untreated, it can progress to confusion, seizures, and coma.
Triggers for both emergencies include infections, heart attacks, strokes, recent surgery, and stopping diabetes medications. An illness you might otherwise shrug off can send blood sugar spiraling when you have diabetes.
Why Your Blood Sugar Might Be High
A single high reading doesn’t always mean something is wrong with your treatment plan. Common, fixable causes include eating more carbohydrates than usual, skipping or mistiming medication, being less active than normal, illness or infection, stress, and poor sleep. Dehydration alone can concentrate glucose in your blood and push readings up.
If you’re seeing high numbers regularly, the pattern matters more than any single reading. Two or three days of readings above your target range is worth a call to your provider. Persistent highs suggest your medication dose, timing, or overall plan may need adjusting. The CDC recommends checking in with your provider every three months if you’re having trouble meeting your blood sugar goals, and your provider may order an A1C test to see how your average levels have been trending.
Preventing the Next Spike
The most reliable way to avoid high blood sugar is to build habits that keep it from climbing in the first place. Walking after meals is the simplest intervention with the most consistent payoff. Even 10 minutes of movement after eating blunts the post-meal spike significantly.
Paying attention to portion sizes with carbohydrate-heavy foods helps too. You don’t need to eliminate carbs, but pairing them with protein, fat, or fiber slows down how quickly glucose enters your bloodstream. A plate of pasta on its own will spike your sugar faster than the same pasta eaten alongside grilled chicken and a salad.
Consistent medication timing matters as much as taking the medication at all. If you’re prescribed something to take before meals and you regularly take it after, or skip doses when you feel fine, your readings will reflect that. Setting a daily alarm or using a pill organizer can help close that gap. Staying hydrated throughout the day, not just when your sugar is already high, gives your kidneys a head start on keeping glucose levels in check.