When your blood sugar is too high, the most effective immediate steps are drinking water, checking for ketones if you’re above 240 mg/dL, and using your prescribed correction dose of insulin if you have one. Hyperglycemia is clinically defined as blood glucose above 140 mg/dL, but most people searching for what to do are dealing with readings well above that, often 200 mg/dL or higher. What you should do depends on how high the number is and whether ketones are present.
Drink Water First
Water is one of the simplest and most underrated tools for bringing blood sugar down. When you’re dehydrated, your body releases a hormone called vasopressin that signals your kidneys to hold on to water. That same hormone has a side effect: it triggers your liver to dump stored sugar into the bloodstream and ramps up cortisol, which pushes blood sugar even higher. Dehydration also activates a second system that interferes with insulin signaling, making it harder for your cells to pull glucose out of your blood.
Drinking water reverses this cycle. It reduces the concentration of glucose in your blood, helps your kidneys flush out excess sugar through urine, and dials back the hormonal signals that were making things worse. There’s no single magic number for how much to drink, but steady sipping over the next hour or two is more effective than gulping a large amount at once. Stick to water or unsweetened beverages.
Take Your Correction Dose If You Use Insulin
If you’re on insulin and your doctor has given you a correction factor, this is when to use it. A correction dose is calculated by taking the difference between your current blood sugar and your target, then dividing by your insulin sensitivity factor. For example, if your sensitivity factor is 45 (meaning one unit of rapid-acting insulin lowers your blood sugar by about 45 mg/dL) and you’re 180 points above target, you’d take 4 units.
Your sensitivity factor is typically calculated using the “Rule of 1800,” which divides 1,800 by your total daily insulin dose. If you don’t already know your correction factor, this is a conversation to have with your care team before your next high reading, so you’re prepared. The key mistake to avoid is “stacking” corrections. Rapid-acting insulin takes time to work. Taking a second correction dose too soon because you’re impatient can send you crashing into low blood sugar a few hours later.
Check for Ketones Above 240 mg/dL
When blood sugar climbs above 240 mg/dL, your body may start breaking down fat for energy instead of glucose, producing acidic byproducts called ketones. This is especially relevant for people with type 1 diabetes, but it can happen in type 2 as well. Urine ketone strips or a blood ketone meter can tell you within seconds whether ketones are building up.
The presence of ketones changes everything about how you handle a high reading, particularly when it comes to exercise. The American Diabetes Association advises avoiding physical activity if your fasting blood sugar is above 250 mg/dL and ketones are present. Even without ketones, use caution if you’re above 300 mg/dL. The reason is counterintuitive: when insulin levels are too low, exercise can actually trigger your body to release even more sugar and ketones into the bloodstream, making the situation worse instead of better.
When Exercise Helps and When It Doesn’t
For moderate highs (under 250 mg/dL with no ketones), light to moderate exercise like a brisk walk can genuinely help. Movement makes your muscles take up glucose from the blood even without insulin, and this effect can last for hours after you stop. A 15 to 30 minute walk after a meal is one of the most practical tools for managing post-meal blood sugar spikes.
But exercise is not a universal fix. If ketones are present, or if your blood sugar is very high and you feel unwell, exercise becomes dangerous. The hormonal stress response from vigorous activity can pour more glucose into your bloodstream faster than your muscles can absorb it. When in doubt, stick to water and insulin and recheck in an hour.
Use Fiber to Blunt Future Spikes
While fiber won’t rescue a blood sugar that’s already high, it’s one of the most effective strategies for preventing the next spike. In a clinical trial involving people with type 2 diabetes, meals containing about 5 grams of soluble fiber produced significantly lower blood sugar responses compared to meals with less than 1 gram. The source of the fiber didn’t matter much. Fiber from whole foods like oats, beans, and fruits worked just as well as a fiber supplement.
Soluble fiber slows the rate at which sugar enters your bloodstream after eating. If you notice your blood sugar consistently spikes after certain meals, adding a fiber-rich food to that meal (a handful of berries, a side of lentils, or oatmeal at breakfast) can meaningfully flatten the curve. This is a long-game strategy, not an emergency intervention, but it reduces how often you find yourself searching for what to do about a high reading.
Set Up Better Alerts If You Use a CGM
If you wear a continuous glucose monitor, your alert settings play a bigger role than most people realize. Research on CGM users with type 1 diabetes found that setting the high-glucose alarm at or below 205 mg/dL was associated with 42% less time spent above 250 mg/dL and 61% less time above 320 mg/dL, compared to those with higher thresholds. The optimal threshold for keeping hyperglycemia under 5% of the day while maintaining an A1c at or below 7% was around 170 mg/dL.
The trade-off is more frequent alerts, which can cause alarm fatigue. But the data showed that tighter high alerts did not increase time spent in low blood sugar, making this a relatively low-risk adjustment. If your current high alert is set at the factory default (often 250 mg/dL or higher), lowering it to 180 or 170 mg/dL gives you an earlier warning and more time to act before things climb further.
Recognize When It’s an Emergency
Most hyperglycemia episodes are manageable at home. But a small percentage escalate into diabetic ketoacidosis (DKA), which is a medical emergency. DKA typically involves blood sugar above 250 mg/dL combined with high ketone levels and a shift in your blood’s acid-base balance.
The symptoms that should prompt a call to emergency services or an immediate trip to the ER include confusion or disorientation, rapid or labored breathing (sometimes described as “air hunger,” where breaths become deep and gasping), persistent vomiting that prevents you from keeping fluids down, and a fruity or acetone-like smell on the breath. DKA can progress from manageable to dangerous within hours, especially in people with type 1 diabetes. If you’re testing positive for moderate to large ketones and can’t get your blood sugar to respond to correction insulin, don’t wait to see if it improves on its own.
Building a Repeatable Action Plan
The best thing you can do for hyperglycemia is have a plan before it happens. That plan should include your target blood sugar range, your correction factor if you use insulin, a supply of ketone test strips that aren’t expired, and a clear threshold for when you’ll call your care team versus handle it yourself. Many people find it helpful to write this out on a card or note in their phone so they’re not trying to do math while feeling lousy.
Track what triggered the high. Common culprits include missed or mistimed medication, underestimating carbs at a meal, illness or infection, stress, and disrupted sleep. Over time, patterns emerge. You might discover that you always spike after rice but not after pasta, or that your blood sugar runs 30 points higher on days you sleep poorly. Those patterns are where lasting control comes from, turning reactive “what do I do right now” moments into proactive prevention.