A blood sugar reading of 500 mg/dL is a medical emergency. At this level, your body is under severe metabolic stress, and you need emergency care immediately. Call 911 or get to an emergency room. Do not try to manage this at home with insulin alone, and do not exercise to bring it down.
Why 500 mg/dL Is Dangerous
Normal blood sugar ranges from about 70 to 140 mg/dL depending on when you last ate. At 500 mg/dL, your blood contains roughly four to five times the normal amount of glucose. Your body can’t use all that sugar, so it starts pulling water out of your cells to try to dilute and flush the excess through your kidneys. This creates a cascade: severe dehydration, dangerous shifts in sodium and potassium levels, and a buildup of acid in your blood.
The potassium shift is particularly risky. As your blood becomes more acidic, potassium moves out of your cells and into your bloodstream. Your blood potassium may look normal or even high on a lab test, but your cells are actually depleted. The average potassium deficit during a crisis like this is 3 to 5 times what your body normally keeps in reserve, and in some cases it can be even worse. This matters because potassium controls your heartbeat, and severe imbalances can cause dangerous heart rhythms or cardiac arrest.
Two Crises That Can Happen
A blood sugar of 500 puts you in the range for two life-threatening conditions, and which one develops depends largely on whether your body is producing ketones.
Diabetic ketoacidosis (DKA) happens when your body, starved of insulin, starts breaking down fat for energy. That process produces waste products called ketones that build up in your blood and make it dangerously acidic. DKA can develop at glucose levels as low as 250 mg/dL and is more common in people with type 1 diabetes, though it can occur in type 2 as well. Symptoms include nausea and vomiting, abdominal pain that can feel like a surgical emergency, deep labored breathing (which occurs in about 28% of cases), and a distinctive fruity smell on the breath.
Hyperosmolar hyperglycemic state (HHS) typically involves even higher blood sugar, often above 600 mg/dL, with extreme dehydration but without significant ketone buildup. HHS is more common in older adults with type 2 diabetes. The hallmark difference is neurological: HHS tends to cause more severe confusion, seizures, and even coma, while DKA more often presents with severe nausea and the characteristic breathing pattern. Both conditions can be fatal without hospital treatment.
Symptoms to Recognize
At 500 mg/dL, you’ll likely experience some combination of these symptoms, and they may have been building for hours or days:
- Extreme thirst and frequent urination: Your kidneys are working overtime to flush excess sugar, pulling water from your body in the process.
- Nausea, vomiting, or stomach pain: Especially common with DKA, the abdominal pain can be intense enough to mimic appendicitis.
- Confusion, drowsiness, or difficulty concentrating: Your brain is sensitive to the chemical changes happening in your blood.
- Rapid heartbeat and low blood pressure: Signs of severe dehydration and volume loss.
- Shortness of breath or heavy breathing: Your body’s attempt to blow off excess acid through the lungs.
- Fruity-smelling breath: A sign that ketones are building up.
- Dry mouth and skin that stays tented when pinched: Indicators of significant fluid loss.
Fatigue, weakness, and unintentional weight loss often precede the crisis by days. If someone with diabetes has been increasingly tired, drinking more water than usual, and urinating frequently, those are warning signs that blood sugar has been climbing.
What to Do Right Now
Call 911 or go to the emergency room. While waiting for help, drink water if you are alert and able to swallow. Dehydration is a major driver of complications at this level, and even small amounts of water can help. Do not eat anything sugary. Do not take extra insulin without medical guidance, because insulin rapidly shifts potassium into your cells, and if your potassium is already depleted, a large dose could trigger a heart rhythm problem.
If you have ketone test strips, check your urine. At glucose levels above 240 mg/dL, the American Diabetes Association recommends testing for ketones. If ketones are present, do not exercise. Physical activity when ketones are high can actually push your blood sugar even higher. Share your ketone results with emergency responders when they arrive.
What Happens at the Hospital
In the ER, treatment focuses on three things simultaneously: bringing your blood sugar down gradually, replacing the fluids you’ve lost, and correcting your electrolyte levels. You’ll receive fluids through an IV to address dehydration, along with carefully dosed insulin to lower glucose at a controlled rate. Doctors will monitor your potassium closely throughout treatment, because as insulin brings your blood sugar down, potassium shifts back into your cells and your blood levels can drop dangerously low. If your potassium is already low when you arrive, the medical team will correct that before giving insulin.
With prompt treatment, DKA typically resolves within 24 hours. Recovery is defined as blood sugar dropping below 200 mg/dL and blood acidity returning to normal. More severe cases can take several days of hospital care. HHS generally takes longer to resolve because the dehydration is more extreme.
Could Your Meter Be Wrong?
Home glucose meters have accuracy limits, especially at very high readings. Under international accuracy standards, a meter is expected to read within 20% of the true value for glucose above 75 mg/dL. At a true value of 350 mg/dL, for example, a meter might display anything from 280 to 360. Most meters max out somewhere between 500 and 600 mg/dL and may simply display “HIGH” instead of a number.
Even accounting for error, a reading of 500 means your blood sugar is dangerously elevated. Whether the true value is 420 or 550, the situation requires emergency care. A reading this high is never a false alarm worth ignoring.
What Causes Blood Sugar to Reach 500
Blood sugar rarely jumps to 500 without a triggering event. The most common causes include missing insulin doses, insulin pump failure, serious infections (which spike stress hormones that raise blood sugar), new-onset type 1 diabetes that hasn’t been diagnosed yet, and major physiological stress like a heart attack or stroke. Some medications, particularly steroids, can also push blood sugar sharply upward.
In people with type 2 diabetes, HHS often develops slowly over days or weeks, with blood sugar climbing gradually while dehydration worsens. Older adults living alone are especially vulnerable because the early symptoms of thirst and fatigue are easy to dismiss. By the time confusion sets in, the person may not be able to recognize or respond to the emergency on their own.