If your blood sugar is too high, the most important first steps are to drink water, check whether you have a correction dose of insulin available (if you use insulin), and monitor your levels closely. For most people with diabetes, “too high” means a reading above 180 mg/dL after a meal or above 130 mg/dL before eating. What you do next depends on how high the number is and what symptoms you’re experiencing.
Drink Water First
Water is the simplest and most immediately helpful thing you can reach for. When blood sugar climbs above roughly 180 mg/dL, your kidneys start dumping the excess glucose into your urine. That process pulls water and electrolytes along with it, which is why high blood sugar makes you urinate frequently and feel dehydrated. Drinking water supports your kidneys in flushing out that extra glucose and replaces the fluid you’re losing.
There’s no precise amount that works for everyone, but steady sipping over the next hour or two is more effective than gulping a large amount at once. Stick to plain water or unsweetened drinks. Dehydration actually makes hyperglycemia worse because reduced urine output means your kidneys can no longer clear the excess sugar efficiently, trapping more glucose in your bloodstream.
Use Your Correction Insulin If You Have One
If you take rapid-acting insulin and your doctor has given you a correction factor, this is when to use it. A correction dose works by calculating how far your current reading is above your target and dividing that gap by your personal insulin sensitivity factor. For example, if your target is 120 mg/dL, your reading is 280 mg/dL, and your correction factor is 40, you’d take 4 units (160 รท 40). This formula, sometimes called the Rule of 1800, is individualized to you. If you don’t already have a correction plan, this is worth discussing with your care team so you’re prepared next time.
After taking a correction dose, wait at least two hours before rechecking. Rapid-acting insulin takes time to work, and stacking doses too quickly is one of the most common causes of a dangerous low later on.
Be Careful With Exercise
Light physical activity like a 15-minute walk can help lower blood sugar by increasing how much glucose your muscles absorb. But there’s an important cutoff. If your reading is above 270 mg/dL, exercise can actually backfire. At that level, your body may be producing ketones, and physical activity can push those levels higher. The Mayo Clinic recommends testing your urine for ketones before working out if you’re above 270. If ketones are present, skip the exercise and focus on hydration and insulin instead.
Know Your Target Numbers
It helps to understand what “too high” actually means in specific terms. The American Diabetes Association recommends these targets for most non-pregnant adults with diabetes:
- Before meals: 80 to 130 mg/dL
- One to two hours after starting a meal: below 180 mg/dL
A reading of 200 mg/dL after a heavy meal that comes back down within a couple hours is a different situation than a fasting reading of 300 mg/dL. Occasional spikes happen. The concern is when levels stay elevated for hours, climb very high (above 300), or come with symptoms that suggest something more serious is happening.
Check for Ketones When Levels Stay High
If your blood sugar remains above 250 to 300 mg/dL despite correction efforts, test your urine for ketones using an over-the-counter test strip. Ketones are acids your body produces when it starts burning fat instead of glucose for fuel, which happens when there isn’t enough insulin available. A small amount of ketones can be managed at home with fluids and insulin, but moderate to large ketones require a call to your doctor right away.
This is especially important if you have type 1 diabetes, where ketone buildup can escalate into diabetic ketoacidosis (DKA) within hours.
Symptoms That Need Emergency Care
Most high blood sugar episodes can be managed at home. But certain symptoms signal that your body is in a dangerous state and you need emergency help immediately:
- Fruity-smelling breath: a hallmark sign of DKA, meaning ketone levels are dangerously high
- Fast, deep breathing: your body’s attempt to compensate for the acid buildup in your blood
- Nausea and vomiting that won’t stop: especially dangerous because you can’t keep fluids or medication down
- Confusion or difficulty staying awake: may indicate severely high blood sugar, sometimes above 600 mg/dL
- Dry skin and mouth with a flushed face: signs of significant dehydration
If you or someone around you notices these symptoms, call 911 or go to the emergency room. DKA and its counterpart in type 2 diabetes (hyperosmolar hyperglycemic state) are both life-threatening without IV fluids and medical-grade insulin management.
What to Do on Sick Days
Illness is one of the most common triggers for unexpectedly high blood sugar. Infections, fevers, and even the common cold cause your body to release stress hormones that raise glucose levels, sometimes dramatically. The CDC recommends checking your blood sugar every four hours when you’re sick and testing your urine for ketones if levels climb. If ketones show up, contact your doctor immediately.
Even if you’re not eating much, don’t skip your diabetes medication or insulin. Many people assume that eating less means they need less insulin, but illness-driven blood sugar spikes happen independently of food. Stay hydrated with water or sugar-free beverages, and keep a log of your readings so you can share them with your care team if the situation doesn’t improve.
Preventing Repeated Spikes
If high blood sugar is becoming a pattern rather than an occasional event, it’s worth looking at the bigger picture. A low-carbohydrate diet, generally in the range of 60 to 130 grams of carbs per day, is one of the most consistently effective strategies for reducing glucose spikes. Regular physical activity improves your body’s sensitivity to insulin over time, meaning the same amount of insulin does more work.
Tracking your blood sugar after meals, not just before them, can reveal which specific foods or portions are causing the biggest jumps. Post-meal readings are often the earliest indicator that glucose control is slipping, and catching that pattern early gives you the chance to adjust before your overall levels drift upward. If lifestyle changes aren’t enough to keep your numbers in range, your doctor may adjust your medication or add a second one to cover the gaps.