When your blood sugar is too high, the most important steps are to hydrate with water, check for ketones if you’re above 240 mg/dL, and take your prescribed insulin or medication if you have one. A blood sugar reading above 180 mg/dL after meals or above 130 mg/dL when fasting is generally considered too high for people with diabetes, though your personal target range may differ. 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 immediate tool you have. When blood sugar runs high, your kidneys work to flush excess glucose out through urine, and staying well hydrated supports that process. High blood sugar also causes dehydration on its own, since frequent urination pulls fluid from your body, creating a cycle that makes things worse.
Start with a full glass of water and continue drinking steadily. The American Diabetes Association recommends drinking water first thing in the morning, before meals, and during exercise, with extra intake when it’s hot or humid. A quick way to gauge your hydration: check the color of your urine. Clear or light yellow means you’re on track. Dark urine means you need more fluids right away. Stick to plain water. Caffeine and alcohol can worsen dehydration.
Take Your Medication if Prescribed
If you use insulin or other glucose-lowering medication, follow your prescribed plan for correcting a high reading. Many people on insulin have a correction dose, which is a small extra amount of fast-acting insulin designed to bring a spike back down. The size of that dose is personalized to you, based on how sensitive your body is to insulin and what your target blood sugar is. If you don’t already know your correction factor, this is something to discuss with your provider at your next visit so you’re prepared.
One important rule: don’t stack correction doses too close together. Fast-acting insulin takes time to work, and taking a second dose before the first has peaked can send your blood sugar crashing in the other direction. If you’ve already taken a correction dose and your numbers aren’t budging after a couple of hours, contact your healthcare provider rather than dosing again on your own.
Check for Ketones Above 240 mg/dL
If your blood sugar reads 240 mg/dL (13.3 mmol/L) or higher, test your urine for ketones using an over-the-counter test kit available at most pharmacies. Ketones are acids your body produces when it starts burning fat instead of glucose for energy, and they can build up to dangerous levels.
A positive ketone test means your body may be moving toward diabetic ketoacidosis (DKA), a serious complication that requires medical attention. Warning signs of DKA include:
- Nausea or vomiting
- Belly pain
- Fruity-smelling breath
- Fast, deep breathing
- Unusual tiredness or weakness
- Confusion
DKA is most common in people with type 1 diabetes but can happen with type 2 as well. If you test positive for ketones and have any of these symptoms, seek emergency care. Don’t try to exercise or “sweat it out,” as physical activity with ketones present can make the situation worse.
Skip Exercise When Blood Sugar Is Very High
Light physical activity like a walk can help lower a moderate blood sugar spike because working muscles pull glucose from the bloodstream. But there’s a ceiling. If your blood sugar is above 270 mg/dL (15 mmol/L), exercise may actually push it higher rather than lower it.
At that level, test for ketones before doing anything physical. If ketones are present, skip the workout entirely and focus on lowering your blood sugar through hydration and medication. Wait until a follow-up ketone test comes back negative before returning to exercise.
For readings between 180 and 270 mg/dL with no ketones, a 15 to 30 minute walk is one of the most effective non-medication strategies to bring levels down. Even gentle movement helps your cells absorb glucose more efficiently.
Adjust What You Eat Next
When your blood sugar is already elevated, what you eat in the next few hours matters. Avoid foods that will add more glucose quickly: bread, pasta, rice, sweetened drinks, fruit juice, and candy are all fast sources of sugar that will compound the spike.
If you need to eat, pair carbohydrates with protein and healthy fat. Protein from sources like eggs, cheese, nuts, fish, or tofu slows the rate at which sugar enters your bloodstream. Fats do the same thing, acting as a brake on digestion. A practical rule of thumb: aim for the protein grams in a meal to be within 10 grams of the net carbohydrate grams. That balance helps prevent another surge on top of the one you’re already managing.
Fiber also helps. Whole grains, vegetables, and legumes contain fiber that acts as a physical barrier around carbohydrates, forcing your digestive system to break them down more slowly. This creates a gentler, more gradual release of glucose compared to refined carbs like white bread or sugary snacks.
Know the Danger Zones
There’s no single universally agreed-upon number that defines a blood sugar emergency. Studies and clinical guidelines have used thresholds ranging from 300 to 400 mg/dL and above to define “severe hyperglycemia,” so context matters more than a single cutoff.
For people managing diabetes day to day, the goal is to spend most of the day with glucose between 70 and 180 mg/dL. Time spent above 250 mg/dL should account for less than five percent of the day. If you’re consistently spending more time above that range, your treatment plan likely needs adjustment.
At the extreme end, readings above 600 mg/dL can signal hyperosmolar hyperglycemic state, a life-threatening condition most common in people with type 2 diabetes. It develops more slowly than DKA, sometimes over days, and causes severe dehydration, confusion, and even loss of consciousness. This always requires emergency care.
Patterns Matter More Than Single Spikes
A single high reading after a big meal isn’t unusual, even for people with well-managed diabetes. What matters more is how often it happens and how long it lasts. If you’re seeing frequent spikes, especially ones that stay elevated for hours, that pattern signals your current medication, diet, or activity level may need to change.
Keep a record of your high readings along with what you ate, when you last took medication, and how active you were that day. This information is far more useful to your provider than a single alarming number. It helps them see whether the issue is a dosage problem, a timing problem, or a dietary pattern, and adjust your plan accordingly.