If your blood sugar is high, the first steps are to drink water, check for ketones if you’re above 240 mg/dL, and take your prescribed medication if you’ve missed a dose or have a correction plan from your care team. Most mild highs come down within a few hours with these steps. But readings above 300 mg/dL, fruity-smelling breath, or vomiting mean you need emergency care right away.
Drink Water First
Water is one of the simplest and most effective first moves when your blood sugar is elevated. When you’re even mildly dehydrated, your blood becomes more concentrated, which means the same amount of glucose shows up as a higher number on your meter. Rehydrating dilutes that effect and helps your kidneys flush excess glucose out through urine more efficiently.
Your kidneys filter blood best when you have enough fluid in your system. Without adequate hydration, glucose builds up instead of being cleared. Drinking water steadily (not all at once) can bring a concentrated reading down within an hour or two by improving kidney function and dilution. Stick to plain water or unsweetened beverages. Juice, soda, or sports drinks will push your sugar higher.
Check Your Medication
A missed dose of insulin or oral medication is one of the most common reasons for a sudden spike. If you realize you’ve skipped a dose, follow whatever guidance your care team has given you for late doses. Don’t double up without clear instructions, because overcorrecting can cause a dangerous low.
If you take insulin and have a correction factor (sometimes called an insulin sensitivity factor) from your diabetes team, you can use it to calculate a small dose that brings your number back toward your target range. The key safety rule here is to avoid “stacking,” which means giving a second correction dose within two hours of the last one. Insulin takes time to work, and stacking doses before the first one peaks significantly raises your risk of a severe low. Tracking the time of each dose, whether on paper, an app, or a smart meter, helps you avoid this.
Know When Exercise Helps and When It Doesn’t
Physical activity is a powerful tool for pulling sugar out of your bloodstream. A walk, light cycling, or other moderate movement can lower your numbers noticeably within 30 to 60 minutes. But there’s an important cutoff: if your blood sugar is above 270 mg/dL, exercise can actually make things worse.
At that level, your body may not have enough insulin available to use the glucose for energy. Instead, it starts breaking down fat, which produces ketones. Exercising with high ketones forces your body deeper into that process and can trigger diabetic ketoacidosis (DKA), a medical emergency. Before exercising with a reading above 270, test your urine for ketones using an over-the-counter test kit. If ketones are present, skip the workout entirely and focus on hydration and your medication plan until they clear.
Test for Ketones Above 240 mg/dL
Ketone testing isn’t just for exercise decisions. The CDC recommends checking for ketones anytime your blood sugar is 240 mg/dL or above, especially if you’re feeling sick. Ketones are acids that build up when your body can’t get enough energy from glucose and starts burning fat instead. A small amount is normal during fasting, but high levels in someone with diabetes signal that something is going wrong fast.
Over-the-counter urine ketone strips are inexpensive and available at most pharmacies. You simply urinate on the strip and compare the color change to the chart on the package. If your result shows moderate or high ketones, contact your doctor or care team promptly. High ketones are an early warning sign of DKA, which can escalate within hours.
Emergency Warning Signs
DKA develops when high blood sugar and high ketones go unchecked. The early symptoms are easy to dismiss: unusual thirst and urinating far more often than normal. But if it progresses, the signs become hard to ignore:
- Fruity-smelling breath, caused by ketone buildup
- Fast, deep breathing
- Nausea, vomiting, or stomach pain
- Dry skin and mouth
- Flushed face
- Extreme fatigue or muscle aches
- Headache or confusion
Call 911 or go to the emergency room if your blood sugar stays at 300 mg/dL or above, your breath smells fruity, you can’t keep food or liquids down, or you’re having difficulty breathing. DKA requires hospital treatment with IV fluids and insulin. It cannot be managed at home once symptoms are severe.
Preventing the Next Spike
A single high reading isn’t unusual. Stress, illness, a larger-than-expected meal, poor sleep, or even hormonal shifts can push your numbers up temporarily. But if you’re seeing frequent highs, it helps to look for patterns. Check your blood sugar at consistent times (before and after meals, at bedtime) for a few days and note what you ate, how active you were, and how you felt. Patterns often reveal the trigger: a particular food, a skipped meal that leads to overeating later, or a time of day when your current medication isn’t covering you well enough.
Carbohydrate-heavy meals cause the sharpest post-meal spikes. Pairing carbs with protein, fat, or fiber slows digestion and blunts the rise. Portion size matters more than food type in many cases. A cup of rice will affect your blood sugar very differently than half a cup.
Consistent physical activity, even 15 to 20 minutes of walking after meals, improves how well your cells respond to insulin over time. This isn’t just a short-term fix. Regular movement lowers your baseline numbers and reduces the frequency of spikes. If you’re doing everything you can with food and activity and still running high, that’s useful information to bring to your care team, because it often means your medication plan needs adjusting.