If your blood sugar is high, the most important immediate steps are drinking water, moving your body (with one key exception), and taking your medication as prescribed. A reading above 240 mg/dL with symptoms like excessive thirst, frequent urination, or fatigue means you should check for ketones and contact your healthcare provider. A reading above 600 mg/dL is a medical emergency.
Check Your Number and Look for Ketones
Before you do anything else, confirm your reading with a blood sugar check. The number matters because it determines which actions are safe. Below 240 mg/dL, you can typically bring your levels down with the strategies below. At or above 240 mg/dL, use an over-the-counter urine ketone test strip. If ketones are present, your body has started breaking down fat for energy in a way that can turn dangerous. Call your provider for guidance on lowering your blood sugar safely, because some of the usual strategies, particularly exercise, can make things worse when ketones are in the picture.
Drink Water Right Away
When blood sugar is elevated, your kidneys work overtime trying to filter out the excess glucose. That process pulls water along with it, which is why high blood sugar makes you urinate more frequently and feel intensely thirsty. Drinking water helps in two ways: it replaces the fluid you’re losing and supports your kidneys in flushing glucose out through urine. Plain water is your best option. Avoid juice, regular soda, or sports drinks, which will push your levels higher.
There’s no single recommended volume, but steady sipping over the next hour or two is more effective than forcing a large amount at once. If you’re already dehydrated from prolonged high blood sugar, you may need more than usual to catch up.
Move Your Body (With One Exception)
Physical activity is one of the fastest non-medication ways to lower blood sugar. When your muscles contract, they pull glucose out of your bloodstream for energy, even without insulin working at full capacity. A 15- to 30-minute walk is enough to make a noticeable difference for many people.
The critical exception: do not exercise if your blood sugar is above 270 mg/dL or if you’ve tested positive for ketones. Exercise in that situation can actually drive blood sugar higher because your body releases stress hormones that trigger the liver to dump more glucose into your blood. If you’re in that range, focus on hydration and contact your provider instead.
Take Your Prescribed Medication
If you use insulin and your provider has given you instructions for a correction dose, follow that plan. A correction dose is a small amount of fast-acting insulin calculated specifically for you based on how sensitive your body is to insulin and how far above your target you are. This calculation is different for everyone, so there’s no universal number. If you don’t already have correction dose instructions, this is worth discussing with your provider at your next visit so you’re prepared.
If you take oral diabetes medication and have missed a dose, that may be the reason for the spike. Take it as soon as you remember, unless it’s close to your next scheduled dose. Don’t double up.
Non-Food Causes You Might Not Expect
If you’re seeing a spike and can’t trace it to what you ate, several other factors could be responsible. Illness and infection are major culprits. When your body fights off a cold, flu, or any infection, it releases stress hormones that raise blood sugar, sometimes dramatically. COVID-19 in particular has been shown to trigger insulin resistance and stress-related blood sugar elevation.
Emotional stress works through the same mechanism. Your body’s fight-or-flight response floods your system with cortisol and adrenaline, both of which signal your liver to release stored glucose. A bad night of sleep, a high-pressure workday, or a family crisis can all show up on your meter.
Certain medications are another common trigger. Steroids (prescribed for conditions like asthma flares, joint inflammation, or autoimmune disorders) cause high blood sugar in 20% to 30% of people who take them, including people who don’t have diabetes. Even a single steroid dose used as an anti-nausea treatment during chemotherapy raises blood sugar in roughly 20% of non-diabetic cancer patients. If you’ve recently started a new medication and notice your numbers climbing, let your provider know.
When High Blood Sugar Becomes an Emergency
Two dangerous complications can develop from prolonged high blood sugar, and both require emergency medical care.
Diabetic ketoacidosis (DKA) develops when your body can’t get enough glucose into cells and starts breaking down fat at a dangerous rate, producing acids called ketones. It’s most common in type 1 diabetes but can happen in type 2 as well. DKA usually builds slowly, but once vomiting starts, it can become life-threatening within hours. Early signs include extreme thirst, frequent urination, and fatigue. As it progresses, you may notice nausea, vomiting, abdominal pain, difficulty breathing, a fruity smell on your breath, and confusion.
Hyperosmolar hyperglycemic state (HHS) is more common in type 2 diabetes and involves blood sugar climbing above 600 mg/dL. At that level, your blood becomes thick and syrupy, and your body can’t use glucose or fat for energy. Confusion and extreme dehydration are hallmarks. HHS develops over days or weeks rather than hours, often in older adults or people who are sick and not drinking enough fluids.
Call 911 or go to an emergency room if your blood sugar stays above 240 mg/dL with positive ketones, you can’t keep food or fluids down due to vomiting or diarrhea, you develop confusion or difficulty breathing, or your reading is above 600 mg/dL.
Preventing the Next Spike
A single high reading is normal and not cause for alarm. Patterns of high readings point to something that needs adjusting. Keeping a brief log of what you ate, your activity level, stress, sleep, and any medications for a few days around high readings often reveals the trigger faster than guessing.
Consistent meal timing, staying hydrated throughout the day, and building regular movement into your routine (even short walks after meals) are the most reliable ways to keep blood sugar steadier over time. If you’re seeing frequent spikes despite doing these things, your medication plan may need updating. Bring your blood sugar log to your next appointment so your provider can spot what’s happening and adjust your treatment accordingly.