Hyperglycemia becomes an emergency when blood sugar climbs high enough to trigger two dangerous conditions: diabetic ketoacidosis (DKA) or hyperosmolar hyperglycemic state (HHS). The key thresholds are blood sugar above 250 mg/dL with ketones present (pointing toward DKA) or above 600 mg/dL (pointing toward HHS). But the number on your meter isn’t the whole picture. What makes hyperglycemia a true emergency is the combination of high glucose with specific symptoms that signal your body is in crisis.
The Blood Sugar Numbers That Matter
There’s no single number where hyperglycemia automatically becomes an emergency, but certain ranges demand immediate action. If your blood sugar is 240 mg/dL or higher while you’re sick, the CDC recommends testing your urine or blood for ketones right away. High ketones at this level are an early warning sign of DKA.
DKA is typically diagnosed when blood sugar exceeds 250 mg/dL and significant ketones are present. Blood ketone levels above 3 mmol/L require immediate emergency treatment. DKA is far more common in people with type 1 diabetes, but it can happen in type 2 as well.
HHS involves even higher glucose levels, usually above 600 mg/dL, and causes severe dehydration without the large ketone buildup seen in DKA. HHS develops more slowly, often over days to weeks, and is more common in older adults with type 2 diabetes. Both conditions are life-threatening without hospital treatment.
Symptoms That Signal a Crisis
Your body gives clear warning signs when hyperglycemia is turning dangerous. Early symptoms include extreme thirst and urinating far more than usual. These happen because your kidneys are working overtime to flush excess sugar, pulling large amounts of water with it. At this stage, you may still be able to manage at home with fluids, insulin adjustments, and close monitoring.
The symptoms that demand emergency care are more severe:
- Nausea and vomiting that won’t stop, which makes it impossible to stay hydrated or keep medication down
- Belly pain, particularly in DKA, which can be intense enough to mimic a surgical emergency
- Fruity-smelling breath, caused by ketones building up in the blood
- Shortness of breath or rapid, deep breathing, which is the body’s attempt to correct rising acid levels
- Confusion, extreme drowsiness, or disorientation, which signal the brain is being affected
- Dry skin and mouth despite drinking fluids, a sign of dangerous dehydration
If you have several of these symptoms together, especially confusion or repeated vomiting, don’t wait to see if things improve. This combination indicates your body’s chemistry is shifting in ways that require IV fluids, electrolyte replacement, and close monitoring that can only happen in a hospital.
Why Confusion Is the Most Urgent Red Flag
Of all the symptoms, changes in mental state are the most alarming. Very high blood sugar can cause delirium, where a person becomes disoriented to time and place, has trouble focusing, and may behave in ways that are completely out of character. In documented cases, people with poorly controlled diabetes have exhibited erratic behavior for days or weeks before anyone connected it to their blood sugar, including wandering at night, talking to themselves, and being unable to maintain attention during conversation.
These neurological symptoms tend to fluctuate throughout the day, often worsening in the evening. In HHS specifically, where blood sugar can climb above 600 mg/dL and severe dehydration concentrates the blood, altered consciousness is a hallmark feature. A person who seems unusually sleepy, confused, or “not themselves” alongside high blood sugar needs emergency care immediately, even before other symptoms appear.
What Triggers a Hyperglycemic Crisis
Knowing what pushes blood sugar into emergency territory can help you stay ahead of it. Infection is the single most common trigger, involved in 30 to 60% of hyperglycemic crises worldwide. Urinary tract infections and pneumonia are the usual culprits. When your body fights an infection, stress hormones surge and drive blood sugar up, sometimes dramatically, even if you’re taking your usual medication.
Missing insulin doses is the other major cause. Even skipping one or two doses can set off a chain reaction in people with type 1 diabetes, where DKA can develop within hours. For people with type 2 diabetes, the slide toward HHS is usually slower but no less dangerous.
Several other situations can tip the balance:
- Acute medical events like a heart attack, stroke, or major trauma
- Corticosteroids (often prescribed for inflammation or autoimmune conditions), which directly counteract insulin
- Certain antipsychotic medications, which can disrupt how the body processes sugar
- A class of diabetes drugs called SGLT2 inhibitors, which have been linked to DKA, sometimes even when blood sugar isn’t extremely high
- Surgery, severe psychological stress, or acute pancreatitis
The combination of illness plus any disruption to your usual insulin routine is especially risky. If you’re sick and your blood sugar is trending upward despite your normal management, start checking ketones and have a low threshold for calling your care team.
DKA vs. HHS: How They Differ
These two emergencies share some features but unfold differently. DKA comes on fast, sometimes within hours. It happens when the body has so little usable insulin that cells can’t access glucose for energy and start burning fat instead. That fat breakdown produces ketones, which are acids. As ketones accumulate, the blood becomes dangerously acidic. Blood sugar in DKA is often in the 250 to 500 mg/dL range, though it can occasionally be lower.
HHS develops gradually, often over a week or more. Blood sugar creeps above 600 mg/dL, and the resulting flood of urination causes profound dehydration. The blood becomes abnormally concentrated. Unlike DKA, significant ketone buildup doesn’t occur because there’s usually enough insulin to prevent the switch to fat burning. The danger in HHS comes from the extreme dehydration and blood concentration, which can lead to seizures, coma, and organ failure. HHS has a higher mortality rate than DKA, partly because it often affects older adults who may not recognize the symptoms as quickly.
What to Do Before You Get to the ER
If your blood sugar is above 240 mg/dL and you feel unwell, test for ketones using an over-the-counter urine or blood ketone kit. Blood ketone meters are more accurate and give results in real time. A reading above 3 mmol/L means you need emergency care now.
While waiting for help or heading to the hospital, sip water if you can keep it down. Dehydration accelerates the crisis because it concentrates sugar in the blood further. Don’t exercise, as physical activity can paradoxically raise blood sugar higher when ketones are present. If you take insulin and know your correction dose, take it, but don’t assume insulin alone will resolve the situation if you already have significant symptoms.
If someone with diabetes is confused, extremely drowsy, or unresponsive, call emergency services rather than trying to drive them to the hospital. Their condition can deteriorate rapidly.
What Happens in the Hospital
Treatment for both DKA and HHS centers on three things: rehydrating the body with IV fluids, bringing blood sugar down with insulin given through an IV, and replacing electrolytes (especially potassium) that get depleted during the crisis. The heavy urination caused by high blood sugar doesn’t just flush water; it pulls essential minerals out with it, and those mineral imbalances can affect heart rhythm and muscle function.
For DKA, treatment typically brings blood sugar below 200 mg/dL and restores normal acid-base balance within 12 to 24 hours, though you may stay in the hospital longer for monitoring. HHS recovery often takes longer because the dehydration is more severe. In both cases, the medical team will look for whatever triggered the crisis, whether that’s an underlying infection, a medication issue, or a gap in insulin therapy, to prevent it from happening again.