If your blood sugar is too high, the most effective immediate steps are drinking water, moving your body, and, if you use insulin, taking a correction dose. What counts as “too high” depends on your situation, but readings consistently above 180 mg/dL after meals or above 130 mg/dL fasting signal hyperglycemia that needs attention. Readings above 250 mg/dL require extra caution, and anything above 600 mg/dL is a medical emergency.
Drink Water First
Water is the simplest tool you have. When your blood sugar is elevated, your kidneys try to flush the excess glucose out through urine, and they need fluid to do it. Dehydration makes the problem worse in two ways: it concentrates the glucose already in your blood, and it triggers your liver to produce even more sugar. Drinking water reverses both of those effects by increasing blood volume (which dilutes glucose concentration) and reducing the hormonal signals that push your liver to release stored sugar.
There’s no precise prescription for how much to drink during a spike, but steady sipping of plain water over the next hour or two is a reasonable approach. Avoid juice, soda, or sweetened drinks, which will push your levels higher.
Move Your Body, With One Important Exception
Physical activity pulls glucose out of your bloodstream and into your muscles, where it gets burned for energy. Even a 15-minute walk after a meal can meaningfully lower a spike. Any movement helps: walking, cycling, housework, or stretching.
The exception: if your blood sugar is above 250 mg/dL, check for ketones before exercising. Ketones are acids your body produces when it starts burning fat instead of glucose, a sign that insulin levels are dangerously low. Exercising with elevated ketones can make blood sugar rise further and push you toward a serious complication called diabetic ketoacidosis. If you don’t have ketone test strips, it’s safer to skip the workout and focus on hydration and medication instead. If ketones are negative or trace, moderate activity is generally fine even at higher readings.
Take a Correction Dose if You Use Insulin
If you’re on rapid-acting insulin, a correction dose can bring your numbers down. The standard approach uses your insulin sensitivity factor, which is how many points one unit of insulin drops your blood sugar. For many people, one unit lowers blood sugar by about 50 mg/dL, but this varies widely, anywhere from 15 to over 100 mg/dL per unit. Your doctor or diabetes educator will have given you your personal number.
The formula is straightforward: subtract your target blood sugar from your current reading, then divide by your sensitivity factor. If your blood sugar is 300 mg/dL, your target is 100, and your factor is 50, you’d take (300 minus 100) divided by 50, which equals 4 units.
Rapid-acting insulin peaks in one to two hours and lasts three to four hours total. Check your blood sugar about two hours after the correction dose to see how it’s working. Resist the urge to take more insulin before that window passes. Stacking doses before the first one has fully kicked in is a common cause of dangerous low blood sugar later on.
If You Don’t Use Insulin
Many people with Type 2 diabetes manage with oral medications, lifestyle changes, or both. When a spike hits, your tools are hydration, movement, and time. Walk for 15 to 30 minutes if your reading is under 250 mg/dL. Drink water steadily. Skip any snacks or carb-heavy foods until your numbers come back down. If you take an oral diabetes medication and you’ve missed a dose, take it as directed.
Longer term, tracking what triggers your spikes gives you the best defense. Eating at regular times matters because skipping breakfast, for example, can raise blood sugar after both lunch and dinner. Choosing foods lower in refined carbs and sugar, using smaller portions, and staying consistent with meals all help prevent the spike from happening in the first place.
When to Check for Ketones
The Joslin Diabetes Center recommends testing for ketones any time your blood sugar is above 250 mg/dL on two consecutive readings. You should also test when you’re sick, since infections and illness commonly trigger sudden high blood sugar and make ketone buildup more likely. Urine ketone strips are inexpensive and available at most pharmacies. Blood ketone meters are more precise but cost more.
If you’re pregnant, test for ketones every morning before breakfast and whenever blood sugar goes above 250 mg/dL.
Know the Warning Signs of a Crisis
Two serious complications can develop from prolonged high blood sugar. Diabetic ketoacidosis, or DKA, happens when the body has too little insulin and begins breaking down fat rapidly, flooding the blood with acids. It can develop at blood sugar levels as low as 200 mg/dL if insulin is severely deficient. Hyperosmolar hyperglycemic state, or HHS, typically involves blood sugar above 600 mg/dL with extreme dehydration but without significant ketone buildup. Both are medical emergencies.
Symptoms of DKA include nausea, vomiting, abdominal pain, deep labored breathing, fruity-smelling breath, and confusion. HHS tends to come on more slowly with extreme fatigue, weakness, and neurological symptoms like confusion, seizures, or loss of consciousness. If you or someone you’re with shows these signs, call emergency services. Don’t try to manage it at home.
Surprising Triggers Worth Knowing
Some blood sugar spikes have obvious causes like a big meal, but others are sneakier. The CDC identifies several that catch people off guard:
- Poor sleep. Even one night of short sleep makes your body use insulin less effectively the next day.
- Caffeine. Black coffee with no sweetener still raises blood sugar in some people.
- Stress and pain. Anything that triggers a stress response, including sunburn, raises blood sugar through hormone release.
- The dawn phenomenon. Your body releases a surge of hormones in the early morning hours that can push fasting blood sugar up before you’ve eaten anything.
- Dehydration. Less water in your body means more concentrated blood sugar, creating a cycle where high glucose causes you to urinate more, dehydrating you further.
- Gum disease. Chronic inflammation in the gums both results from and worsens blood sugar control.
- Nasal decongestant sprays. Some contain chemicals that signal your liver to release more glucose.
Knowing your personal triggers lets you act before a spike becomes a problem. Keeping a simple log of your blood sugar alongside meals, sleep, stress, and activity for even a week or two often reveals patterns that are easy to address once you see them.