When to Go to the Hospital for High Blood Sugar

High blood sugar becomes a hospital-level emergency when it climbs high enough to push your body into a metabolic crisis, most commonly diabetic ketoacidosis (DKA) or hyperosmolar hyperglycemic state (HHS). As a rough guide, a reading persistently above 300 mg/dL that does not respond to your usual correction dose, especially when paired with symptoms like vomiting, confusion, or heavy breathing, warrants an emergency room visit. But the number on your meter is only part of the picture, and in some situations your blood sugar can be deceptively close to normal while a dangerous acid buildup is already under way.

The Two Emergencies You Need to Know About

There are two distinct crises that send people with dangerously high blood sugar to the hospital. They share some features but develop differently, affect different populations more often, and carry different warning signs.

DKA happens when the body has so little working insulin that cells cannot take in glucose for fuel. The body pivots to burning fat at an accelerated rate, which floods the bloodstream with acidic byproducts called ketones. Classic symptoms include nausea, vomiting, lethargy, altered mental status, and abdominal pain, along with a distinctive fruity odor on the breath caused by the ketone acetone.¹ DKA is most closely associated with type 1 diabetes, but it can also occur in type 2, particularly during severe illness or when insulin is skipped.

HHS tends to develop more slowly, over days or even weeks, and is more common in older adults with type 2 diabetes. In HHS, the body still produces some insulin, enough to prevent the massive fat-burning and acid buildup of DKA, but not enough to keep blood sugar anywhere near a safe range. The persistently elevated glucose causes enormous fluid loss through the kidneys. Thirst alone usually cannot keep up with the losses, and as dehydration worsens, kidney function declines, trapping even more glucose in the blood. The cycle can push blood sugar to extreme levels and lead to severe dehydration, confusion, seizures, and coma.² Because HHS comes on gradually, people sometimes attribute the early symptoms to a stomach bug or simple fatigue, which delays the trip to the ER.

Specific Warning Signs That Mean “Go Now”

Knowing when to stop managing at home and call 911 or drive to the hospital can be lifesaving. The following signs suggest a hyperglycemic emergency is developing or already present:

Persistent readings above 300 mg/dL: If your blood sugar stays above 300 after a correction dose of insulin and adequate hydration over two to three hours, the situation is not self-correcting.
Moderate or large ketones: A urine ketone strip reading moderate or large, or a blood ketone meter reading above 1.5 mmol/L, signals that your body is breaking down fat for fuel at a dangerous rate.
Vomiting that prevents fluid intake: You cannot rehydrate or keep oral medications down, which accelerates dehydration and acid buildup.
Rapid or labored breathing: Deep, gasping breaths (sometimes called Kussmaul breathing) are the body’s attempt to blow off excess acid. This is a late and serious sign.
Confusion or drowsiness: Altered mental status indicates the brain is affected, either by acidosis or by the extreme dehydration of HHS.
Abdominal pain with nausea: Especially in combination with high blood sugar and ketones, this pattern points toward DKA.
Fruity breath odor: The acetone smell is a hallmark of ketone overproduction.¹

Any one of these in isolation is a reason to be alert. Two or more together, especially confusion or persistent vomiting, should prompt an emergency room visit without waiting to see if things improve.

What Pushes Blood Sugar Into the Danger Zone

Most hyperglycemic emergencies do not come out of nowhere. They are triggered by something identifiable, which means many are preventable if you know what to watch for.

Infection is the single most common trigger. In one study of hospitalized DKA patients, infections triggered about 62% of episodes.³ Urinary tract infections, pneumonia, and skin infections are common culprits. The stress hormones your body releases to fight infection directly counteract insulin, driving blood sugar up even when you are eating less than usual. This is a crucial point: many people reduce or skip insulin when they are sick and not eating, which is exactly the wrong move during an infection.

Missed or inadequate insulin is the other major driver. In a separate analysis, poor treatment compliance was responsible for over half of DKA admissions.⁴ Sometimes people run out of insulin and cannot afford a refill. Sometimes they skip doses because they feel fine. And sometimes the delivery mechanism fails: insulin pump users face a unique risk because they carry no long-acting insulin reservoir, meaning an infusion set kink or failure can lead to rapidly rising glucose within hours.⁵

Other triggers include new-onset diabetes (sometimes DKA is the event that leads to a first diagnosis), surgery, certain medications like corticosteroids, heavy alcohol use, and emotional or physical stress. Being aware of these triggers, especially during an illness, gives you a head start on catching a crisis before it fully develops.

Checking Ketones at Home

Testing for ketones is the single most useful thing you can do at home when your blood sugar is climbing and not responding to corrections. Ketone levels tell you whether your body is sliding toward DKA, and that information determines whether you can manage the situation at home or need professional help.

There are two ways to test: urine strips and blood ketone meters. Blood meters are generally considered more accurate and timely because they measure beta-hydroxybutyrate, the most abundant ketone in DKA, in real time. Urine strips measure acetoacetate, which can lag behind what is actually happening in the blood by several hours. A study comparing the two in people with type 1 diabetes found that ketosis was detected significantly more often during urine monitoring periods than during blood monitoring periods, suggesting urine testing may overcount ketones in some situations while also catching them less precisely in real time.⁶

If you have type 1 diabetes, keeping a blood ketone meter in your supplies is worth the investment. Most endocrinologists recommend checking ketones whenever your glucose is above 250 mg/dL and especially during illness. A blood ketone reading below 0.6 mmol/L is normal. Between 0.6 and 1.5 is a caution zone where extra insulin and fluids are needed with close monitoring. Above 1.5 mmol/L is a strong signal to contact your care team or head to the ER, and above 3.0 is a medical emergency.

When Blood Sugar Looks Normal but the Danger Is Real

One of the trickiest scenarios in diabetes emergencies is euglycemic DKA, where dangerous ketone buildup occurs even though blood sugar is below 300 mg/dL or sometimes even in a nearly normal range. This form of DKA is particularly insidious because its latent onset, combined with nonspecific symptoms like mild nausea or fatigue, can delay diagnosis and treatment until the situation becomes severe.⁷

The primary culprit behind euglycemic DKA in recent years is a class of diabetes medications known as SGLT2 inhibitors (brand names include Jardiance, Farxiga, and Invokana). These drugs work by causing the kidneys to dump excess glucose into the urine, which lowers blood sugar effectively. But the glucose-lowering effect can mask the underlying metabolic problem. By clearing glucose from the blood, SGLT2 inhibitors keep the number on your meter looking reassuringly low even as ketone production ramps up behind the scenes. The drugs also promote fluid and sodium loss, worsening dehydration, and appear to elevate glucagon levels, which further encourages the body to make ketones.⁸

If you take an SGLT2 inhibitor, the standard advice of “check ketones when blood sugar is above 250” may not protect you. You should also check ketones whenever you feel nauseous, unusually fatigued, or short of breath during illness, even if your glucose reading looks fine. Surgeons and anesthesiologists often recommend stopping SGLT2 inhibitors several days before a planned procedure for this reason. The awareness gap around euglycemic DKA remains a real clinical problem: patients feel reassured by acceptable glucose readings, and even some emergency departments can initially miss the diagnosis if they focus on the glucose number rather than the acid-base picture.

Pregnancy and High Blood Sugar Emergencies

Pregnant women with diabetes face a heightened risk that deserves its own discussion. Pregnancy-related DKA can develop at lower glucose levels and progress more quickly than in non-pregnant adults, and it carries significant adverse outcomes for both mother and baby.⁹ The hormonal changes of pregnancy, particularly rising levels of cortisol and human placental lactogen, increase insulin resistance substantially in the second and third trimesters. At the same time, the placenta consumes glucose, which can lower the mother’s blood sugar readings even as insulin demand skyrockets.

The practical implication is that a pregnant person with diabetes should have a lower threshold for seeking emergency care. Persistent glucose above 200 mg/dL during pregnancy, particularly with any ketones, warrants urgent medical evaluation. Vomiting during pregnancy is so common that it can mask DKA symptoms, making it easy to dismiss early signs as typical morning sickness. The fetal risk from maternal DKA is high and includes fetal distress and loss, so erring on the side of caution here is not overcautious, it is appropriate.

What Happens When You Arrive at the ER

Understanding what treatment looks like can help reduce the anxiety of a hyperglycemic emergency. When you arrive at the hospital with suspected DKA or HHS, the treatment team focuses on three immediate priorities: replacing fluids, bringing down blood sugar with intravenous insulin, and correcting electrolyte imbalances.

Fluid replacement comes first because dehydration is often severe, especially in HHS. Intravenous saline begins quickly, sometimes at rates of a liter per hour initially, to restore circulation and help the kidneys start clearing excess glucose. Intravenous insulin follows, delivered at a carefully controlled rate rather than as a large bolus, to bring blood sugar down gradually and safely.

One thing that may surprise you: potassium management is just as critical as glucose management in these emergencies. Insulin drives potassium from the blood into cells, and if your potassium level drops too low, it can cause dangerous heart rhythms or weaken the muscles needed for breathing. Emergency teams aim to keep serum potassium in a safe range and will often replace potassium before or alongside starting insulin.¹⁰ This is why DKA and HHS require hospital-level care rather than just a bigger dose of insulin at home: the electrolyte shifts can be life-threatening on their own.

Recovery from DKA typically takes 12 to 24 hours with appropriate treatment, though some people need longer. HHS recovery is often slower because the dehydration is more extreme and the patients tend to be older with more underlying health conditions.

Risks of Waiting Too Long

Delayed treatment for a hyperglycemic emergency raises the risk of complications substantially. In DKA, prolonged acidosis can lead to cerebral edema, particularly in children, where the main finding in fatal cases is damage related to disruption of the blood-brain barrier and increased permeability of brain blood vessels.¹¹ This is one reason pediatric DKA is treated with particular urgency. In HHS, the mortality rate is notably higher than in DKA, partly because the patients are older and partly because the extreme dehydration can trigger blood clots, kidney failure, and cardiovascular collapse.

The evidence here is unambiguous: outcomes are better the earlier treatment starts. If you are debating whether to go in, that hesitation is itself a signal. People who die from hyperglycemic emergencies almost always had hours of recognizable warning signs that were dismissed or attributed to something else.

Insulin Pump Users and Technology Gaps

Insulin pump therapy offers excellent blood sugar control for many people, but it introduces a specific vulnerability. Because pumps deliver only rapid-acting insulin with no long-acting background, any interruption in delivery, whether from a kinked cannula, an air bubble, a dislodged infusion set, or a dead battery, means insulin delivery stops completely. Blood sugar can begin climbing within an hour and reach dangerous levels within three to four hours.

Research on infusion set failures found that the patterns of rising glucose were variable and unpredictable, making them hard to catch by feel alone. When failure-detection alarms were modeled, they could have reduced the time spent above 180 mg/dL by roughly 29%.⁵ Newer closed-loop (hybrid or fully automated) pump systems with continuous glucose monitors do a better job of alerting users, but no system is infallible. If you use a pump and your blood sugar rises sharply without an obvious cause like food, the first step is to give a correction dose with a syringe or pen rather than through the pump, and change your infusion site. If the spike does not start to reverse within an hour, check ketones.

The Insulin Access Problem

It would be irresponsible to discuss when to go to the hospital for high blood sugar without acknowledging that some people end up in the ER because they could not afford to stay out of it. In the United States, cost-related insulin rationing, skipping doses, delaying refills, or using less insulin than prescribed to make a supply last, affects a meaningful number of adults with diabetes. A national survey estimated that roughly 1.3 million adults under age 65 with diabetes reported rationing insulin because of cost.¹²

Missing even a single day of basal insulin can be enough to set DKA in motion for someone with type 1 diabetes. If cost is a barrier to staying on your insulin, several practical options exist. Manufacturer patient assistance programs, state-level insulin price cap laws (many U.S. states have now capped copays at $35 per month for insured patients), urgent-fill provisions at pharmacies, and community health center sliding-scale programs can all help. The Inflation Reduction Act also capped insulin copays at $35 for Medicare beneficiaries. Knowing about these resources before you are in crisis is far better than discovering them in the ER.

Preventing Repeat Admissions

If you or your child has been hospitalized for DKA, the risk of it happening again is real. A hospital-based quality improvement program that combined structured education with a switch to longer-acting insulin and school-based follow-up reduced DKA readmission rates by about 31% over 11 months.¹³ The results suggest that readmissions often come down to gaps in the system, not just individual compliance. Ensuring follow-up within a week of discharge, confirming that prescriptions were actually filled, and having a written sick-day plan are practical steps that reduce the odds of another emergency.

A sick-day plan is worth having written down and posted somewhere visible. The basics: never stop basal insulin during illness, check blood sugar every two to four hours, check ketones if glucose stays above 250, drink fluids aggressively even if you do not feel thirsty, and know the specific blood sugar and ketone thresholds at which your care team wants you to call them or go to the ER. Having that plan on paper means you do not have to make judgment calls when you are already feeling terrible.

When You Are Unsure

Many people hesitate to go to the ER because they do not want to overreact or take up resources. It helps to frame the decision around a few concrete questions rather than trying to interpret symptoms in the moment. Is your blood sugar above 300 and not coming down after a correction dose and an hour or two? Do you have moderate or large ketones? Are you unable to keep fluids down? Are you confused, breathing unusually hard, or feeling significantly worse than a typical bad day? If the answer to any of those is yes, you are not overreacting by going to the hospital. If you take an SGLT2 inhibitor, add another question: do you have unexplained nausea, fatigue, or labored breathing even with a glucose reading that looks acceptable?

For people who live alone, the threshold should be even lower. DKA and HHS can alter consciousness, and the window between “I feel off” and “I cannot help myself” can close faster than expected. Telling a friend or family member your sick-day plan and asking them to check in during illness is a simple step that has saved lives.

1
PubMed. Early Detection of Diabetic Ketoacidosis by Breathalyzer in a Sailor Reporting for Duty
2
AACE Endocrinology and Diabetes. Beyond the Limits: Severe Hyperglycemia in Hyperosmolar Hyperglycemic State (Serum Glucose 2375 mg/dL) – Section: Discussion
3
PubMed Central. PRECIPITATING FACTORS AND SYMPTOMS IN PATIENTS WITH DIABETIC KETOACIDOSIS
4
Saudi Medical Journal. Precipitating factors for diabetic ketoacidosis – Section: Results
5
PubMed Central. Early Detection of Infusion Set Failure During Insulin Pump Therapy in Type 1 Diabetes
6
PubMed Central. Blood versus urine ketone monitoring in a pediatric cohort of patients with type 1 diabetes: a crossover study – Section: Results
7
PubMed Central. Ketoacidosis and SGLT2 Inhibitors: A Narrative Review
8
BMJ. Euglycemic diabetic ketoacidosis in the era of SGLT-2 inhibitors – Section: Pathophysiology
9
Obstetric Anesthesia Digest. Diagnosis and Management of Euglycemic Diabetic Ketoacidosis in Pregnancy – Section: Abstract
10
Society for Academic Emergency Medicine. Hyperglycemia – Section: POTASSIUM REPLACEMENT
11
PubMed. Cerebral edema in children with diabetic ketoacidosis: vasogenic rather than cellular?
12
PubMed Central. Cost-Related Insulin Rationing in US Adults Younger Than 65 Years With Diabetes
13
PubMed Central. Reducing Diabetic Ketoacidosis Readmissions with a Hospital-School-Based Improvement Partnership