If your blood sugar is high, the most important first steps are drinking water, checking for ketones if your reading is above 240 mg/dL, and avoiding exercise until you know it’s safe. What counts as “high” depends on timing: the American Diabetes Association recommends blood sugar stay between 80 and 130 mg/dL before meals and below 180 mg/dL one to two hours after eating. Anything consistently above those targets is hyperglycemia.
Start With Water
Dehydration and high blood sugar feed off each other. When your blood sugar is elevated, your kidneys work harder to filter out excess glucose, pulling water from your body in the process. Drinking water helps your kidneys flush that extra sugar through urine and prevents you from getting more dehydrated.
If you have type 2 diabetes, drink fluids steadily throughout the day. If you’re having trouble keeping water down, take small sips every 15 minutes. For type 1 diabetes, aim for a glass of sugar-free liquid every hour, especially if you’re vomiting or have diarrhea. Avoid sugary drinks, juice, and regular soda, which will push your blood sugar even higher.
Check for Ketones Above 240 mg/dL
When your body can’t use glucose properly, it starts burning fat for energy instead. That process creates ketones, acidic byproducts that can build up in your blood to dangerous levels. If your blood sugar is 240 mg/dL or above, use an over-the-counter urine ketone test strip to check. These are available at most pharmacies without a prescription.
The test strip will show results as a specific number or a general reading of “small,” “moderate,” or “large.” A positive result at any level means your body has started shifting toward a dangerous state called diabetic ketoacidosis (DKA), and you should contact your doctor about how to bring your blood sugar down safely. Large amounts of ketones are life-threatening.
Ketone testing is especially critical for people with type 1 diabetes. If your blood sugar is above 300 mg/dL, check your urine for ketones every three hours until the results are negative for at least six hours. You should also test immediately if you notice any of these symptoms: nausea or vomiting, rapid breathing, fruity-smelling breath or urine, extreme thirst, stomach pain, or unusual sleepiness and confusion.
Don’t Exercise Until You Check
Light physical activity can help lower blood sugar in many situations, but there’s an important exception. If your blood sugar is over 270 mg/dL, exercise can actually make things worse. At that level, your body may already be producing ketones, and physical activity increases ketone production. That raises your risk of ketoacidosis.
Before exercising with a reading above 270, test your urine for ketones first. If ketones are present, skip the workout entirely. Take steps to lower your blood sugar (hydration, medication if prescribed), then wait until a follow-up ketone test shows a negative result before you exercise. If your blood sugar is elevated but below 270 and you have no ketones, a walk or other light activity can help bring your levels down.
Take Your Medication as Prescribed
A high reading is often a sign that something in your routine shifted. You may have missed a dose of medication, eaten more carbohydrates than usual, been less active, or experienced stress or illness. If you take insulin, follow the correction dose your doctor has given you. Don’t take extra medication beyond what’s been prescribed, since overcorrecting can cause a dangerous low blood sugar crash.
If you’re getting frequent high readings, that’s worth a conversation with your doctor. It often means the dosage or timing of your medication needs adjusting, not that you’re doing something wrong.
Warning Signs That Need Emergency Care
Most episodes of high blood sugar can be managed at home with fluids, ketone monitoring, and medication adjustments. But certain combinations of symptoms signal a medical emergency. The CDC recommends going to the emergency room or calling 911 if:
- Your blood sugar stays at 300 mg/dL or above and isn’t coming down
- Your breath smells fruity, which signals ketone buildup
- You’re vomiting and can’t keep food or drinks down
- You’re having trouble breathing or breathing very rapidly
- You have ketones in your urine, even if your blood sugar has come back to normal
These are signs of diabetic ketoacidosis, which is most common in type 1 diabetes but can occur in type 2 as well. DKA develops when ketone levels get high enough to make your blood acidic. It requires IV treatment in a hospital and can be fatal if untreated.
A Rarer Emergency in Type 2 Diabetes
People with type 2 diabetes face a different kind of crisis when blood sugar climbs extremely high, typically above 600 mg/dL. At that level, the body becomes severely dehydrated, and neurological symptoms appear: extreme drowsiness, confusion, weakness, and sometimes seizures (which occur in up to 25% of cases). This condition progresses over days or weeks rather than hours, so it often develops gradually in people who haven’t been monitoring their blood sugar closely. It requires emergency treatment and is most common in older adults.
Preventing the Next Spike
Once your blood sugar is back in range, it helps to figure out what caused the spike so you can avoid it next time. The most common triggers are straightforward: a missed or mistimed medication dose, a higher-carb meal than expected, physical or emotional stress, an illness or infection, or dehydration. Even a common cold can raise blood sugar significantly because your body releases stress hormones to fight the infection.
Keeping a simple log of your blood sugar readings alongside what you ate and any unusual circumstances can reveal patterns that aren’t obvious in the moment. Many people discover, for example, that certain meals they assumed were moderate in carbohydrates consistently cause spikes, or that their blood sugar runs higher on days they sleep poorly. These patterns give you and your doctor concrete information to work with when adjusting your plan.
If you’re regularly seeing readings above 180 mg/dL after meals or above 130 mg/dL before meals, that’s a sign your overall management plan may need updating, whether that means a medication change, a shift in meal timing, or more consistent physical activity.