What Are Hyperglycemia and Hypoglycemia?

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Low blood sugar (glucose) levels, called hypoglycemia, can cause fatigue or even fainting. Hypoglycemia is more common for individuals with diabetes and may result from too much medication, not eating enough, or overexercising.

The opposite effect, hyperglycemia (high blood sugar levels), happens during times of stress or poorly-controlled diabetes. If left untreated, hyperglycemia damages organs throughout the body.

Blood sugar is regulated by the pancreas, a long gland in the abdomen. The pancreas produces a hormone called insulin which facilitates cellular uptake of blood sugar.

Insulin helps to transform the food you eat into energy that your body can use. If your body doesn’t produce insulin or becomes resistant to insulin’s effects, you may experience blood sugar issues.

Person using blood sugar meter to check glucose levels

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Hyperglycemia and Hypoglycemia Types

The pancreas maintains the flow of glucose between your bloodstream and your cells. In diabetes, the flow is out of balance, either not producing insulin (type 1 diabetes) or not responding to insulin (type 2 diabetes).

Type 1 diabetes is an autoimmune disease usually diagnosed early in life, while type 2 diabetes takes time to develop. The early stage of type 2 diabetes is called prediabetes.

Gestational Diabetes

Type 2 diabetes symptoms may show up during pregnancy, which is a condition called gestational diabetes. Gestational diabetes usually goes away after giving birth but indicates a higher diabetes risk in the future.


Early symptoms of hyperglycemia may go unnoticed, especially in the case of type 2 diabetes. However, in type 1 diabetes, blood sugar elevations can quickly turn into a dangerous condition called ketoacidosis.

Low blood sugar can also become a life-threatening situation for people with diabetes. Here’s what you can expect in high and low blood sugar episodes.


Early symptoms of hyperglycemia include:

  • Blurred vision 
  • Frequent urination (peeing)
  • High blood sugar 
  • Increased thirst and hunger 

Hyperglycemia may leave you feeling weak and tired. Slow-healing cuts and sores, vaginal or skin infections, and weight loss can also be attributed to chronically elevated blood sugar levels.

Ketoacidosis Symptoms

Ketoacidosis may cause:

  • Deep labored breathing or hyperventilation 
  • Dehydration
  • Rapid heartbeat 
  • Unusual fruity smell on the breath (acetone breath)
  • Vomiting


Hypoglycemia symptoms can start out minimal and develop rapidly into a health crisis. Symptoms of hypoglycemia may vary but are most dangerous for individuals with type 1 and type 2 diabetes.

Hypoglycemia may cause:

  • Anxiety or nervousness
  • Blurred or impaired vision 
  • Color draining from the skin (pallor) 
  • Confusion 
  • Coordination problems, clumsiness 
  • Dizziness, lightheadedness
  • Fast heartbeat 
  • Headaches
  • Hunger 
  • Irritability or impatience 
  • Low energy
  • Nausea 
  • Nightmares or crying out during sleep 
  • Seizures
  • Sleepiness
  • Shakiness
  • Sweating, chills, and clamminess 
  • Tingling or numbness in the lips, tongue, or cheeks 


Causes vary for hyperglycemia and hypoglycemia.


A few different scenarios can produce hyperglycemia, but in prediabetes or type 2 diabetes, the primary cause is poor insulin sensitivity. Unlike in type 1 diabetes, where not enough insulin is produced, type 2 diabetes is often characterized by high insulin levels.

The body may be overproducing insulin. As a result, the cells become desensitized to it, meaning it’s unable to do its job of bringing high blood sugars down.

Blood sugar goes up after a meal, especially if that meal contains simple carbohydrates. Sugary beverages are particularly prone to spiking blood sugars since there’s no fiber, fat, or protein to slow digestion.

Once sugar is broken down and released into the bloodstream, insulin is released to push it into the cells for quick energy or storage. When insulin isn’t working well, blood sugar stays high in the blood until it’s eventually filtered out through the kidneys.

Other causes of hyperglycemia include:

  • Dawn phenomenon caused by hormones produced in the early morning 
  • Emotional stress 
  • Gestational diabetes
  • Illness, such as a cold or infection
  • Insufficient dosage of diabetes medications
  • Medical conditions affecting the pancreas or endocrine system (like pancreatitis or Cushing syndrome)
  • Steroids or other medications 
  • Surgery or trauma


Hypoglycemia may be caused by overdosing on insulin or diabetes medications, or if you eat less than usual after taking diabetes medications.

Just as eating too many carbohydrates can cause blood sugars to rise, eating too few carbohydrates or skipping and delaying meals (especially after taking insulin or medications) can cause low blood sugars.

Intense physical activity can also cause hypoglycemia as your muscles use sugar from the blood to fuel exercise. Further, alcohol disrupts the balance of blood sugar and may mask the early symptoms leading to hypoglycemia.


Hyperglycemia can be detected in a fasting state or after a meal.

Fasting blood sugar levels above 125 mg/dL indicate diabetes. Usually, fasting blood tests are performed first thing in the morning following an overnight fast (meaning eight hours without food). Fasting levels between 100 mg/dL to 125 mg/dL are borderline high and may suggest prediabetes.

Blood sugars rise after a meal. One to two hours after eating, blood sugars should be back down to 180 mg/dL or less. Higher than 180 mg/dL is hyperglycemia.

Another method for tracking high blood sugar is the hemoglobin A1C test. Hemoglobin A1C reflects average blood sugar control over the past three months. Measured in a percentage, an A1C level between 5.7% and 6.4% is a sign of chronic hyperglycemia and may indicate prediabetes. A reading of 6.5% or higher indicates diabetes.

Hypoglycemia is usually diagnosed when blood sugar drops below 70 mg/dL. Not everyone shows symptoms at this level, and some people exhibit symptoms before blood sugars get this low. Serious hypoglycemia causes neurological symptoms, like confusion and lethargy.  


Treatment varies for hyperglycemia and hypoglycemia.


Hyperglycemia can be treated immediately with exercise or medication or treated longer-term through dietary changes and losing excess body weight. If lifestyle changes are unsuccessful, your healthcare provider may suggest starting or adjusting your treatment plan.

If blood sugars are above 240 mg/dL, you may be advised to check for ketones and hold off on working out.


Fast-acting carbohydrates reverse hypoglycemia in a matter of minutes. Sugary foods without fat or protein are quickly converted into sugar, boosting low blood levels. Glucose tablets or gel, fruit juice, regular soft drinks, honey, and sugary candy are a few examples.

Once consumed, blood sugars should be rechecked in 15 minutes and retreated if they have not risen above 70 mg/dL. If blood sugars are moving in the right direction, a more balanced snack or meal can help maintain stable blood sugars.

In the case of very low blood sugar, most people are not capable of treating themselves. A medication called glucagon can be administered by injection. Glucagon forces blood sugar to be released by the liver, quickly restoring the blood to safe levels.

Working with your healthcare provider will help you avoid sudden spikes and dips in blood sugar that require emergency treatment.


Untreated hyperglycemia can damage the nerves, blood vessels, tissues, and organs. High blood sugars raise heart attack and stroke risk and lead to blindness and kidney disease.

Luckily, regular monitoring with blood sugar and A1C tests makes it possible to adjust your treatment plan and ward off the negative long-term effects of high blood sugar (while also preventing dangerous lows).


Blood sugar fluctuations can be scary and frustrating. Finding others with similar struggles can make it easier to cope with a diabetes diagnosis. Ask your provider about group education for type 1, type 2, or gestational diabetes to learn more about your condition and get tips from those who get it.

With a little trial and error and your healthcare team’s support, managing blood sugar doesn’t have to feel overwhelming.

11 Sources
Verywell Health uses only high-quality sources, including peer-reviewed studies, to support the facts within our articles. Read our editorial process to learn more about how we fact-check and keep our content accurate, reliable, and trustworthy.
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By Anastasia Climan, RDN, CD-N
Anastasia, RDN, CD-N, is a writer and award-winning healthy lifestyle coach who specializes in transforming complex medical concepts into accessible health content.