If your blood sugar is high, the first steps are to hydrate with water, avoid eating more carbohydrates, and check whether your reading has crossed into a range that needs medical attention. A reading between 180 and 250 mg/dL is considered high, while anything above 250 mg/dL is very high and requires extra caution. What you do next depends on how high the number is and whether you’re experiencing symptoms.
Check Your Number and Know the Thresholds
Not all high readings carry the same urgency. A blood sugar of 200 mg/dL after a large meal may come down on its own within a couple of hours. A reading that stays above 250 mg/dL, especially if you feel unwell, is a different situation entirely.
At 240 mg/dL or above, you should test your urine for ketones using an over-the-counter test kit from any pharmacy. Ketones are acids your body produces when it starts burning fat for energy instead of glucose, and their presence signals that your body isn’t processing sugar correctly. A positive ketone test means you’re at risk for a dangerous condition called diabetic ketoacidosis, and you should contact your doctor right away.
If your blood sugar is at or above 300 mg/dL and won’t come down, that’s emergency territory, especially if you’re also vomiting, having trouble breathing, or notice a fruity smell on your breath.
Start Drinking Water Immediately
When blood sugar climbs too high, your kidneys try to flush the excess glucose out through urine. This pulls water and important minerals like sodium and potassium along with it, which is why high blood sugar makes you urinate frequently and feel intensely thirsty. The result is a cycle: high glucose causes fluid loss, and dehydration concentrates the sugar in your blood even further.
Drinking water is one of the simplest and most effective things you can do during a spike. It helps your kidneys clear glucose and counteracts the dehydration that makes everything worse. Stick to plain water. Avoid juice, soda, sweetened coffee drinks, and even flavored waters with added sugar.
Skip the Carbs for Now
While your blood sugar is elevated, avoid foods that will push it higher. The obvious culprits are bread, pasta, rice, and sweets, but some less obvious ones catch people off guard. Sugar-free baked goods still contain flour, which raises blood sugar. Sweetened nondairy milks add carbohydrates. Specialty coffee drinks with milk and flavored syrups can contain as much sugar as a dessert.
If you’re hungry, choose something with protein and healthy fat, like eggs, nuts, cheese, or avocado. These take longer to digest and won’t drive your glucose up further. When you do eat carbohydrates again, pairing them with protein or fat at the same meal helps slow the rise in blood sugar compared to eating carbs alone.
Move Your Body, but Only If It’s Safe
Physical activity pulls glucose out of your bloodstream and into your muscles, making it one of the fastest natural ways to bring a reading down. Even a 15- to 20-minute walk can make a noticeable difference.
There’s one important exception. If your blood sugar is above 270 mg/dL, test for ketones before exercising. If ketones are present, do not exercise. Working out with ketones in your system can actually make your blood sugar climb higher and push you toward ketoacidosis. Wait until your ketones clear and your glucose comes down before being active.
If You Take Insulin, Avoid Stacking Doses
If you use rapid-acting insulin, you may be tempted to take a correction dose and then take another one an hour later when the number hasn’t budged. This is called insulin stacking, and it’s one of the most common causes of dangerous low blood sugar in people who use insulin.
Rapid-acting insulin takes 10 to 30 minutes to start working, peaks around one to two hours later, and stays active in your body for about four hours total. If you take a second correction dose within three hours of the first, the two doses overlap and can drive your blood sugar far lower than intended. The Joslin Diabetes Center recommends waiting three to four hours before giving yourself another correction. It feels slow when you’re staring at a high number, but the insulin is working even when the reading hasn’t dropped yet.
What to Do When You’re Sick
Illness is one of the most common triggers for stubborn high blood sugar. Infections, colds, the flu, and even minor illnesses cause your body to release stress hormones that raise glucose levels. You may see numbers climb even if you’re eating less than usual.
When you’re sick, check your blood sugar every four hours and keep a written log. Test your urine for ketones at least once, and call your doctor if ketones are present. Continue taking your diabetes medication or insulin even if you’re not eating much. Dehydration during illness is a serious risk, so keep sipping water, broth, or electrolyte drinks throughout the day.
When High Blood Sugar Is an Emergency
Most high readings can be managed at home with hydration, food choices, movement, and patience. But certain combinations of symptoms mean you need emergency care immediately:
- Blood sugar above 300 mg/dL that won’t come down
- Fruity-smelling breath, which signals ketone buildup
- Vomiting that prevents you from keeping food or fluids down
- Difficulty breathing or fast, deep breaths
- Extreme fatigue, confusion, or muscle stiffness
These are warning signs of diabetic ketoacidosis, which can become life-threatening within hours if untreated. Don’t wait to see if it improves on its own. Call 911 or go to the emergency room.
Preventing the Next Spike
A single high reading is usually manageable. Repeated highs point to something that needs adjusting. Common causes include eating larger portions than planned, missed or mistimed medication, stress, poor sleep, and illness. Tracking your blood sugar alongside what you eat and how you feel can reveal patterns you wouldn’t notice otherwise.
If your blood sugar is frequently above 180 mg/dL after meals or above 130 mg/dL when fasting, your medication, meal plan, or both may need to change. Keeping a log for a week or two before your next appointment gives your doctor real data to work with rather than a single snapshot.