If your blood sugar is high, the most effective immediate steps are drinking water, moving your body, and checking whether you need a correction dose of insulin (if you use it). What counts as “high” and how urgently you need to act depends on the number. A fasting blood sugar above 126 mg/dL meets the threshold for diabetes, readings above 250 mg/dL require ketone testing, and anything over 600 mg/dL is a medical emergency.
Know Your Number and What It Means
Not all high readings demand the same response. A reading of 180 mg/dL after a big meal is a different situation than a reading of 350 mg/dL with no clear cause. Here’s a rough framework:
- 130–180 mg/dL (fasting or pre-meal): Mildly elevated. Often manageable with hydration, movement, and dietary adjustments.
- 180–250 mg/dL: Moderately high. Take action with the steps below and recheck in a few hours.
- Above 250 mg/dL: Test for ketones if you have Type 1 diabetes or use insulin. If ketones are present, do not exercise and contact your care team.
- Above 600 mg/dL: Call 911. This level can trigger a dangerous condition called hyperosmolar hyperglycemic state (HHS), which causes severe dehydration, confusion, and loss of consciousness.
Drink Water Right Away
When blood sugar is elevated, your kidneys try to flush the excess glucose through urine. That’s why frequent urination and intense thirst are two of the earliest symptoms of high blood sugar. This cycle pulls fluid from your body quickly. Drinking water helps your kidneys do their job and prevents the dehydration that makes hyperglycemia worse. Aim for a full glass immediately and keep sipping steadily over the next few hours. Avoid juice, soda, or anything with added sugar.
Go for a Short Walk
Physical activity pulls glucose out of your bloodstream and into your muscles, where it gets burned for energy. You don’t need a gym session. Research from the Cleveland Clinic found that even two to five minutes of walking after eating produces a measurable drop in blood sugar. A 10 to 15 minute walk is better still. The key is light, steady movement: a walk around the block, some gentle stretching, or even pacing around the house.
There is one important exception. If your blood sugar is above 300 mg/dL, do not exercise. At that level, your body may not have enough insulin available to let your muscles use the glucose, and exercise can actually push blood sugar higher. If you have ketones in your urine or blood at any level, skip exercise entirely until they clear.
Use Your Insulin Correction Dose
If you take rapid-acting insulin, a correction dose is the standard tool for bringing down a high reading. The basic math works like this: subtract your target blood sugar from your current reading, then divide by your correction factor. Your correction factor (sometimes called insulin sensitivity factor) tells you how much one unit of insulin will lower your blood sugar. For many people, one unit drops glucose by about 50 mg/dL, but individual sensitivity ranges widely, from 15 to over 100 mg/dL per unit.
For example, if your blood sugar is 250 mg/dL, your target is 100, and your correction factor is 50, the math is: (250 minus 100) divided by 50 equals 3 units. Your doctor or diabetes educator should have given you a personalized correction factor. If you’ve never calculated a correction dose before, this isn’t something to figure out on your own for the first time during a spike. Call your care team for guidance.
After taking a correction dose, wait at least two to three hours before rechecking. Stacking insulin doses too close together is a common cause of dangerous low blood sugar later on.
Check for Ketones Above 250 mg/dL
When your body can’t get enough glucose into cells (usually because of insufficient insulin), it starts breaking down fat for energy instead. This produces ketones, acidic byproducts that build up in the blood. This is most relevant for people with Type 1 diabetes, but it can also happen in Type 2 under certain conditions.
The Joslin Diabetes Center recommends testing for ketones any time your blood sugar is above 250 mg/dL on two consecutive tests. You can check with urine test strips (available at most pharmacies) or a blood ketone meter. If ketones are moderate or large on a urine strip, or above 1.5 mmol/L on a blood meter, contact your doctor or go to urgent care. Ketoacidosis can develop within hours and causes nausea, vomiting, abdominal pain, fruity-smelling breath, and rapid breathing.
Recognize the Symptoms
High blood sugar doesn’t always announce itself dramatically. The earliest signs are easy to miss or attribute to something else: increased thirst, frequent urination, a headache, or slightly blurred vision. You might just feel “off.” These symptoms tend to appear when blood sugar has been elevated for several hours.
If high blood sugar persists over days or weeks, the symptoms shift. Persistent fatigue, unexplained weight loss, slow-healing cuts, recurring yeast infections, and skin infections all point to chronically elevated glucose. These are signs that your management plan needs adjustment, not just a one-time correction.
The severe end of the spectrum is harder to miss. Nausea, vomiting, confusion, rapid heartbeat, and deep labored breathing are warning signs of ketoacidosis (most common in Type 1) or hyperosmolar hyperglycemic state (more common in Type 2, typically at blood sugars above 600 mg/dL). Both are medical emergencies.
Adjust What You Eat Next
While you’re waiting for your blood sugar to come down, don’t eat more carbohydrates. If you’re hungry, reach for something with protein, healthy fat, or fiber. Soluble fiber is especially useful because it forms a gel-like substance in your stomach that slows digestion and blunts future glucose spikes. Good sources include oats, black beans, avocados, apples, and Brussels sprouts. The CDC recommends 22 to 34 grams of fiber daily, and most people fall well short of that.
For the meal that may have caused the spike, think about what you’d do differently. A plate heavy on white rice, bread, or pasta without much protein or fat hits the bloodstream fast. Pairing carbohydrates with fiber, protein, or fat slows absorption significantly. This won’t fix the current spike, but it’s the most practical long-term strategy for preventing the next one.
Track the Pattern, Not Just the Spike
A single high reading after a big holiday meal is different from readings that consistently land above 180 mg/dL. If you’re seeing frequent highs, log the time, what you ate, your activity level, and any stress or illness. Patterns almost always emerge: maybe your blood sugar always climbs after breakfast but not dinner, or maybe it spikes on days you skip your afternoon walk.
Illness, stress, poor sleep, and certain medications (like steroids) all raise blood sugar independently of what you eat. If you’re sick with an infection or a cold, expect higher readings and check more frequently. The Joslin Diabetes Center recommends rechecking every three to four hours during illness, with ketone testing if readings exceed 250 mg/dL.
Bring your logged data to your next appointment. Specific patterns give your care team something concrete to work with, whether that means adjusting medication timing, changing doses, or rethinking your meal plan. A single high reading is a problem to solve in the moment. A pattern of high readings is a signal that something in your overall plan needs to change.