Dangers of Uncontrolled Blood Sugar

Medically Reviewed by Shruthi N, MD on June 03, 2024
7 min read

Uncontrolled blood sugar, or blood glucose, is a level that's outside of a healthy target range. It usually refers to blood sugar that's too high, which is a symptom of diabetes. Both extremely high and extremely low blood sugar are dangerous.

Glucose is the main source of energy for your cells. You get most of it from carbohydrates in the things you eat and drink. When you eat, your body releases the hormone insulin, which helps your cells absorb glucose. People with diabetes aren't able to manage their blood glucose effectively because either their bodies don't make enough insulin (type 1 diabetes) or their cells don't respond to insulin (type 2 diabetes).

If your blood sugar is too high for too long, it can cause serious health problems. It’s something to be careful of whether you have diabetes or not.

Your doctor will tell you what your target range should be and what to do if your levels aren’t in that range. If you have diabetes, you'll need to check your blood sugar regularly to know if it’s too high, too low, or meets your goal.

What are dangerous blood sugar levels in diabetes?

Different people will have different target levels for their blood sugar. But generally, for people with diabetes, a level of 180 milligrams per deciliter (mg/dL) within 2 hours of eating is considered too high. That's called hyperglycemia. The higher it goes, the more dangerous it becomes.

For most people, blood sugar below 70 mg/dL is considered too low and is called hypoglycemia. Anything below 40 mg/dL is life-threatening.

Diabetes is the main reason for high blood sugar, but there are other possible causes, such as some medications, problems with your pancreas, an overactive thyroid, and certain rare tumors.

When your blood sugar is too high, you may not notice anything wrong right away. Symptoms can take days or weeks to develop. They include:

  • Feeling thirstier than usual
  • Blurred vision
  • Having to pee more often
  • Feeling hungrier than normal

You might also feel more tired than usual, get infections on your skin, or notice that cuts and sores take a long time to heal.

If you take insulin or other drugs to lower your blood sugar, you're at risk of it dropping too low. That can happen if you're exercising or if you skip a meal, even if you don't have diabetes. Other things can also cause your blood sugar to drop too low, including drinking alcohol, certain medications, serious heart, liver, or kidney diseases, hormone problems, and weight-loss surgery.

When you have low blood sugar, you may be:

  • Shaky or jittery
  • Pale or sweaty
  • Confused, anxious, or irritable
  • Hungry
  • Tired
  • Dizzy or lightheaded

You may also have a headache and a fast or irregular heartbeat. Without treatment, you can lose consciousness or have a seizure. 

You can get your blood sugar back up by having something to eat or having a sugary drink such as soda or fruit juice. You can also take glucose tablets.

High glucose levels can affect you from head to toe. If they're out of control for a long time, you could have some or all of the following:

  • Heart disease or heart attack
  • Stroke
  • Kidney damage
  • Nerve damage
  • Eye damage
  • Skin problems

Both extremely high and extremely low blood sugar can become a medical emergency. If you don't treat it quickly, an episode of either hyperglycemia or hypoglycemia could cause you to lose consciousness. That's called a diabetic or diabetes-related coma. If someone you know has diabetes and loses consciousness, call 9-1-1.

You may be able to keep uncontrolled blood sugar from becoming an emergency by recognizing the warning signs and getting help. 

Symptoms of low blood sugar will probably improve if you have something to eat or drink with sugar. If that doesn't help, get a ride to your doctor's office or call 9-1-1.

High blood sugar may cause two emergency conditions that have different symptoms.

Diabetic ketoacidosis (DKA)

When your insulin is low and your cells aren't able to access the sugar in your blood to use for energy, your body starts burning fat. That produces chemicals called ketones. When these build up, your blood becomes more acid-like. This can be life-threatening if it’s not treated. It's more common with type 1 diabetes and can happen quickly when you're sick.

Symptoms of DKA include:

  • Trouble breathing
  • Vomiting
  • Being very tired
  • Stiff or achy muscles
  • Extreme thirst or a very dry mouth
  • Having to pee too often
  • Dry or flushed skin
  • Breath that smells like fruit
  • Confusion

If your blood sugar measures over 240 mg/dL, you should use an at-home test to measure the level of ketones in your urine. A moderate or high result warrants a call to your doctor so they can tell you what to do. You may need to go to the emergency room.

Hyperosmolar hyperglycemic syndrome (HHS)

This dangerous condition involves extremely high blood sugar levels -- 600 mg/dL or higher. It requires immediate emergency treatment.

As glucose builds up in your blood, your body tries to get rid of it through your urine. At first, you pee a lot. Over time, you pee less, and when you do, it’s very dark. HHS causes your blood to thicken and makes you severely dehydrated. Other symptoms include:

  • Extreme thirst that may later go away
  • Warm, dry skin that doesn’t sweat
  • A fever over 101 F
  • Sleepiness or confusion
  • Weakness on one side of your body
  • Vision loss
  • Hallucinations

HHS mostly affects people over age 65 and people whose diabetes isn't well controlled. It can happen when you're sick, especially with an infection.

If your blood sugar numbers are often too high or too low, talk to your doctor about whether you need to adjust your diabetes treatment.

If you have DKA, your doctor might be able to talk you through steps to correct it at home. But with severe symptoms, you'll need to be treated at a hospital. Emergency treatment is the same for both DKA and HHS. You'll get:

  • Fluid delivered through a vein in your arm (IV). This replaces fluid you lost from urinating more often and lowers the concentration of sugar in your blood.
  • Electrolytes such as potassium
  • Insulin treatment

You may need tests to find out why your blood sugar got so high.

With low blood sugar, if you can't raise it on your own or if you lose consciousness, you'll need emergency treatment. You may get a shot of glucagon, a hormone that tells your liver to release stored sugar into your blood. You could also get a sugar solution delivered directly into your blood through an IV.

Doctors recommend that everyone over age 35 get their blood sugar tested at least every 3 years to look for signs of diabetes. If you have diabetes, you can take steps to protect yourself from the dangers of uncontrolled blood sugar.

Work with your doctor. Know your target blood sugar ranges and what to do if the readings are too high. Ask what to do when you're sick. Follow your doctor’s advice about diet and exercise, and keep up with care appointments.

Check your blood sugar regularly. Your doctor will tell you how often you need to test. A continuous glucose monitor tests your blood every few minutes and can help you stay on top of blood sugar swings.

Take your medication. Follow your doctor's instructions for taking insulin or other medications. Many high and low blood sugar emergencies come from missing insulin doses or taking too much. An insulin pump can be set to deliver the drug on a set schedule.

Educate yourself. Many things can affect your blood sugar levels, including what you eat and drink, your activity level, medications you take, illness and stress, and hormone fluctuations. When you understand how your body reacts to changes, you can adjust your medication or eating plan to keep your blood sugar stable.

Pay attention to your diet. Understand the role that different nutrients play in blood sugar highs and lows. For example, carbohydrates can spike blood glucose, while fiber helps regulate it. Know how often you need to eat, and carry appropriate snacks in case you get off schedule.

Even if you don't have diabetes, cutting down on sweets and unrefined carbs and staying physically active can keep your blood sugar steady.

Blood sugar that swings either too high or too low is a common problem when you have diabetes. When it happens suddenly, it can cause you to lose consciousness or even die. Over time, high blood sugar can lead to serious complications including heart attack or stroke, nerve damage, kidney failure, and blindness. You can keep your blood sugar in control by monitoring your levels and following your diabetes treatment plan.

What are the consequences of uncontrolled blood sugar?

Over time, blood sugar that's too high can cause health problems including cardiovascular disease, nerve damage, kidney damage, and vision problems. If it comes on quickly, extremely high or low blood sugar could cause a diabetic coma.

How do you feel when your blood sugar is too high?

You might not notice any symptoms if you have high blood sugar. But it often causes you to be extra thirsty or to pee more often than usual.

When should you go to the ER for blood sugar?

Uncontrolled blood sugar can lead to several emergency situations. One is called diabetic ketoacidosis, which means your blood sugar is high, and you also have chemicals called ketones in your urine. A reading over 600 is an indication of hyperglycemic hyperosmolar syndrome and needs to be treated immediately. Extremely low blood sugar can cause you to lose consciousness, in which case you'd need emergency care.