If your blood sugar is too high, the most important first steps are to hydrate with water, check for ketones if you can, and use your prescribed correction insulin if you have one. A reading that stays at or above 300 mg/dL, especially with symptoms like nausea, fruity-smelling breath, or vomiting, is a medical emergency.
What counts as “too high” and what you should do about it depends on how high the number is, how long it’s been elevated, and whether you’re showing additional symptoms. Here’s how to work through it.
Immediate Steps for a High Reading
Drink water. This is the simplest and most universally helpful response to high blood sugar. When glucose builds up in your blood, your kidneys try to flush it out through urine, which dehydrates you. Dehydration then concentrates your blood sugar further, creating a cycle. Steady sips of plain water help your kidneys do their job and can meaningfully bring levels down over a few hours.
If you take rapid-acting insulin and your doctor has given you a correction dose formula, use it. The general principle is that one unit of rapid-acting insulin lowers blood sugar by roughly 50 mg/dL, but this varies widely from person to person, anywhere from 15 to 100 mg/dL per unit. Your own correction factor should come from your diabetes care team, not guesswork. If you don’t already have a correction plan, a persistent high reading is a good reason to ask for one at your next appointment.
Avoid stacking corrections. If you took insulin and your number hasn’t budged in 30 minutes, resist the urge to take more right away. Rapid-acting insulin can take up to two hours to fully work. Taking additional doses too soon is one of the most common causes of a dangerous low-sugar crash afterward.
Check for Ketones
When your body can’t use glucose properly, it starts burning fat for energy instead. That process produces ketones, acidic byproducts that build up in your blood. High ketones are an early warning sign of diabetic ketoacidosis (DKA), a life-threatening condition that can develop within hours.
If your blood sugar is above 250 mg/dL, test your urine or blood for ketones using an over-the-counter test strip. If ketones are moderate or high, don’t try to manage it at home. Call 911 or go to the emergency room.
One critical detail: do not exercise when ketones are present. While physical activity normally helps lower blood sugar, it can actually trigger ketoacidosis when ketone levels are already elevated. The Mayo Clinic advises that blood sugar over 270 mg/dL is a caution zone where you should test for ketones before any physical activity.
Know the Emergency Thresholds
Not every high reading is an emergency, but certain combinations of numbers and symptoms are. Go to the emergency room or call 911 if:
- Your blood sugar stays at 300 mg/dL or above and isn’t coming down with your usual correction plan.
- Your breath smells fruity. This is a hallmark sign that ketones are building up in your blood.
- You’re vomiting and can’t keep food or fluids down. This makes it impossible to rehydrate or take oral medication, and the situation can spiral quickly.
- You’re having trouble breathing or notice fast, deep breaths you can’t control.
DKA symptoms also include dry skin and mouth, flushed face, headache, muscle stiffness, stomach pain, and extreme fatigue. Multiple symptoms appearing together raise the urgency significantly.
A separate emergency called hyperosmolar hyperglycemic state (HHS) occurs primarily in people with type 2 diabetes when blood sugar climbs above 600 mg/dL. HHS develops more slowly than DKA, often over days, but is equally dangerous. It causes severe dehydration, confusion, and can lead to seizures or coma. Blood sugar over 600 mg/dL requires emergency care regardless of how you feel.
Why Your Blood Sugar Spiked
The obvious culprits are food-related: a high-carb meal, miscounted carbohydrates, or a missed insulin dose. But several less obvious triggers cause spikes that catch people off guard.
Illness and infection are among the most powerful. When your body fights off a cold, flu, urinary tract infection, or any other illness, it releases stress hormones that raise blood sugar. People with diabetes often need higher insulin doses when they’re sick, even if they’re eating less than usual.
Stress works through the same mechanism. Physical stress (like a sunburn or an injury) and emotional stress (a difficult week at work, poor sleep) both trigger your body to release cortisol and adrenaline. These hormones tell your liver to dump stored glucose into your bloodstream, a survival response that becomes a problem when you can’t process that glucose efficiently.
The dawn phenomenon is another common cause of unexplained morning highs. In the early morning hours, your body naturally releases a surge of hormones that raise blood sugar to help you wake up. Everyone experiences this, but people with diabetes often can’t compensate for the spike. If your fasting numbers are consistently high despite eating well the night before, this is likely why.
Other triggers include dehydration, certain medications (steroids are a major one), skipped or spoiled insulin, and even changes in your menstrual cycle. Identifying your personal pattern of triggers makes it much easier to prevent spikes rather than chase them after the fact.
Using Activity to Lower Blood Sugar
Physical activity is one of the fastest non-medication tools for bringing blood sugar down. When your muscles contract, they pull glucose out of your blood for fuel, with or without insulin. A 15-to-30-minute walk after a meal can noticeably blunt a post-meal spike.
But there are important guardrails. If your blood sugar is over 270 mg/dL, test for ketones before exercising. If ketones are present, exercise will make things worse, not better. And if your blood sugar drops to 70 mg/dL or below during activity, stop immediately and treat the low.
For moderate highs (say, 180 to 250 mg/dL with no ketones), a brisk walk, light cycling, or even housework can help bring numbers down within 30 to 60 minutes. You don’t need intense exercise. Gentle, sustained movement works well.
Preventing Repeated Highs
A single high reading is a data point. Repeated highs are a pattern that needs attention. If you’re seeing numbers above 180 mg/dL regularly, particularly two hours after meals or first thing in the morning, your current management plan likely needs adjustment.
Start by logging your readings alongside what you ate, your activity level, stress, sleep, and any illness. Patterns usually emerge within a week or two. You might discover that certain meals spike you more than expected, or that your morning readings climb on nights when you sleep poorly.
Bring this log to your diabetes care team. Adjustments might include changing the timing of your medication, updating your correction factor, shifting your meal composition, or adding a new tool like a continuous glucose monitor. Your insulin sensitivity changes over time due to weight changes, aging, activity level, and other medications, so a plan that worked six months ago may not be the right fit now.
Carbohydrate awareness matters more than strict restriction for most people. Pairing carbs with protein, fat, or fiber slows digestion and flattens the blood sugar curve. Eating the same number of carbs as a piece of grilled chicken with rice versus a bowl of plain rice can produce very different glucose responses.