When your blood sugar is high, the most effective immediate steps are drinking water, moving your body (if it’s safe to do so), and rechecking your levels before making further corrections. A reading above 180 mg/dL after a meal is generally considered elevated, and anything that stays above 300 mg/dL is a medical emergency that warrants a call to 911 or a trip to the ER.
What you should do next depends on how high the number is, whether you take insulin, and how you’re feeling physically. Here’s how to work through it step by step.
Drink Water First
Water is the simplest and most immediate thing you can reach for. When your body is dehydrated, it produces hormones that tell the kidneys to conserve water, and those same hormones appear to impair glucose processing. Research from Arizona State University found that when water-conservation hormones were stimulated, participants had 10% to 15% higher blood sugar levels than when they were well hydrated. The underlying reason likely involves the liver producing more glucose, the muscles absorbing less of it, or both.
Staying hydrated also helps your kidneys flush excess glucose through urine. Choose plain water over juice, soda, or sports drinks, all of which add sugar and make the problem worse. There’s no magic number of glasses you need, but drinking steadily over the next hour or two is a reasonable approach.
Move Your Body (With One Important Check)
Light physical activity, like a 15- to 20-minute walk, helps your muscles pull glucose out of the bloodstream for energy. This can bring levels down noticeably within an hour. But there’s a threshold where exercise becomes dangerous rather than helpful.
If your blood sugar is above 270 mg/dL, check for ketones before you exercise. Ketones are acids your body produces when it starts burning fat instead of glucose, usually because there isn’t enough insulin available. You can test for them with an inexpensive urine strip from any pharmacy. If ketones are present, do not exercise. Physical activity when ketone levels are elevated can trigger a serious condition called diabetic ketoacidosis. At that point, you need medical guidance, not a walk around the block.
If You Take Insulin, Be Patient
If you use insulin and have taken a correction dose, resist the urge to stack another dose on top of it too quickly. Joslin Diabetes Center defines insulin stacking as giving a correction within three hours of a previous one, and it’s a common cause of dangerous low blood sugar later on. Wait three to four hours before re-correcting. The insulin is likely still working, even if the number on your meter hasn’t budged yet.
Recheck your blood sugar at that three- to four-hour mark. If it’s still elevated, a second correction may be appropriate. If you’re unsure about dosing, this is a good time to call your care team rather than guess.
Adjust What You Eat Next
You can’t undo a spike, but you can keep it from climbing further. The next time you eat, prioritize foods that slow carbohydrate absorption rather than accelerate it.
Soluble fiber is especially helpful here. It dissolves in water and forms a gel-like substance in your stomach, which slows digestion and blunts the rise in blood sugar. Good sources include oats, black beans, lima beans, apples, bananas, avocados, and Brussels sprouts. Insoluble fiber, found in whole wheat, bran, nuts, seeds, and fruit and vegetable skins, helps increase insulin sensitivity over time.
Pairing carbohydrates with protein and healthy fat also slows the rate at which glucose enters your bloodstream. A handful of nuts alongside a piece of fruit, for example, produces a much gentler blood sugar curve than the fruit alone. If your blood sugar is currently high, skipping refined carbohydrates like white bread, crackers, or sweetened drinks at your next meal makes a meaningful difference.
When to Check for Ketones
Ketone testing isn’t something you need to do every time your blood sugar runs a little high. But two situations call for it: when your blood sugar is 240 mg/dL or above and you’re feeling sick, or when it’s above 270 mg/dL and you’re considering exercise.
Over-the-counter urine ketone strips are inexpensive and available without a prescription. You urinate on the strip and compare the color change to a chart on the packaging. Results are typically reported as small, moderate, or large amounts of ketones. A “small” reading with blood sugar that’s trending down may not require emergency action. A “moderate” or “large” reading, especially combined with symptoms like nausea, stomach pain, or fruity-smelling breath, means you need medical help right away.
Symptoms That Signal an Emergency
Most high blood sugar episodes resolve with water, activity, time, or an insulin correction. But some situations are genuinely dangerous. Diabetic ketoacidosis can develop quickly, and its early signs are easy to mistake for the flu or general fatigue.
Early warning signs include urinating much more than usual, extreme thirst or hunger, dehydration, and headache. If left untreated, more severe symptoms appear:
- Fast, deep breathing
- Fruity-smelling breath
- Nausea or vomiting
- Stomach pain
- Confusion or extreme sleepiness
- Dry skin and mouth
- Flushed face
Call 911 or go to the emergency room if your blood sugar stays at 300 mg/dL or above, your breath smells fruity, you’re vomiting and can’t keep fluids down, or you’re having trouble breathing. High ketone levels combined with any of these symptoms are life-threatening and require immediate treatment.
Patterns Matter More Than Single Readings
A one-time spike after a large meal or a stressful day is not the same as a persistent pattern of high readings. If you’re seeing elevated numbers regularly, the issue is usually something systemic: your medication dose may need adjustment, your carbohydrate intake may be higher than you realize, or stress and poor sleep may be working against you.
Tracking your readings alongside what you ate, how you slept, and how active you were gives you and your care team real data to work with. Many people find that a few consistent changes, like adding a short walk after meals, swapping refined grains for whole grains, or drinking water throughout the day rather than only at meals, bring their numbers into a noticeably better range within weeks.