Hyperglycemia means high levels of blood sugar, also known as blood glucose. Over time, it can cause major health complications in people with diabetes.

Several factors can contribute to hyperglycemia, including dietary choices and a sedentary lifestyle.

Regular blood glucose testing is crucial for people with diabetes. This is because many people don’t feel the effects of hyperglycemia.

Fasting hyperglycemia vs. postprandial (after-meal) hyperglycemia

The World Health Organization explains that “normal” blood sugar readings range between 70 and 100 milligrams per deciliter (mg/dL) while fasting, or not eating.

Readings between 100 and 125 mg/dL classify as impaired fasting hyperglycemia. If you have two or more blood glucose tests performed in a fasting state that are at or above 126 mg/dL, you may have diabetes.

On the other hand, high blood sugar after eating is called postprandial, or after-meal, hyperglycemia. Your readings within a couple of hours after eating reflect how your body reacts to the foods you consume. According to a 2018 study, regular high blood sugar readings after meals or snacks may be an early sign of type 2 diabetes.

There is also a relationship between fasting hyperglycemia and postprandial hyperglycemia. In the same 2018 study, researchers explained that if a person has fasting hyperglycemia, they may also experience “markedly exaggerated” postprandial hyperglycemia.

According to the Centers for Disease Control and Prevention (CDC), target blood glucose levels for people with diabetes are typically:

  • between 80 and 130 mg/dL before you’ve eaten
  • under 180 mg/dL 2 hours after the first bite of your meal

Blood sugar levels that are higher than that may indicate uncontrolled diabetes.

However, you may not feel the effects of hyperglycemia until your blood glucose levels are very high for an extended period of time. If you experience symptoms of hyperglycemia, it’s important that you check your blood glucose levels.

Hyperglycemia symptoms that may develop over several days or weeks include:

The longer the condition is left untreated, the more severe it may become. Long-term effects of hyperglycemia include:

  • eye disease
  • kidney disease
  • cardiovascular disease
  • neuropathy, or nerve damage

When to contact a doctor

Diabetic ketoacidosis (DKA) and hyperglycemic hyperosmolar syndrome (HHS) are two conditions caused by very high glucose levels. Contact a doctor if you suspect you’ve developed DKA or HHS.

The hallmarks of DKA are elevated ketones, acidic substances in the blood and urine, and acidosis, a state where blood becomes acidic. According to a 2013 review, DKA is typically diagnosed in adults with a blood glucose level over 250 mg/dL. A 2015 study indicates that DKA is diagnosed in children with a blood glucose level over 200 mg/dL.

DKA generally occurs in people with type 1 diabetes and is less common with type 2 diabetes. However, not everyone with these blood glucose levels will have DKA.

In addition to the usual symptoms of hyperglycemia, a person with DKA may also have:

People with HHS typically have a blood glucose level over 600 mg/dL, according to a 2017 review. In addition to excessive thirst and urination, symptoms may include:

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A number of things can contribute to hyperglycemia, including:

  • not getting the right dosage of insulin or other glucose-lowering medication
  • eating more carbohydrates than usual
  • being less physically active than usual
  • illness or infection
  • high levels of stress
  • physical trauma, such as an orthopedic injury

Dawn phenomenon

You may experience regular episodes of high blood sugar in the early morning hours between 3 and 8 a.m., before you have eaten anything, according to the American Diabetes Association. This is called the dawn phenomenon, and researchers say it’s important to note your levels during this period of time.

Why? The dawn phenomenon occurs due to higher levels of hormones like cortisol and growth hormone. These hormones signal the liver to make more glucose, so you have the energy that helps you wake up.

If your levels are high, it may be because you have diabetes or your diabetes is not well managed.

The American Diabetes Association says that if you experience episodes of hyperglycemia in the mornings only occasionally, they may not affect your A1C, a kind of blood glucose test. If they become a frequent occurrence, your A1C levels may move higher, into a concerning range.

Risk factors for hyperglycemia include:

Several treatments are available for hyperglycemia.

Monitor your glucose levels

An important part of managing your diabetes is checking your blood glucose levels often, such as before you eat, after you eat, or at bedtime.

Then, record that number in a notebook, blood glucose log, or blood glucose tracking app so you and your doctor can monitor your treatment plan.

Knowing when your blood glucose levels are getting out of your target range can help you get your blood glucose back on track before more significant complications arise.

Get moving

Exercise is one of the best and most effective ways to keep your blood glucose levels where they should be and lower them if they get too high.

If you’re on medications that increase insulin, talk with your doctor to determine the best times to exercise. If you have complications such as nerve or eye damage, ask your doctor which exercises might suit you best.

An important note: If you have had diabetes for an extended period of time and are on insulin therapy, talk with your doctor to see if there are any exercises you should limit when your blood glucose levels are high.

For example, the American Diabetes Association says that if your blood glucose level is above 240 mg/dL, your doctor may have you check your urine for ketones.

Don’t exercise if you have ketones. According to the Diabetes Research Institute, your doctor may also tell you not to exercise if your blood glucose is above 250 mg/dL even without ketones.

Exercising when ketones are in your body may cause your blood glucose level to rise even higher. While it’s rare for those with type 2 diabetes to experience this, it’s still best to be cautious.

Analyze your eating habits

Work with a dietitian or nutritionist to construct a nutritious, interesting selection of meals that can help you manage your carbohydrate intake and prevent higher blood glucose levels.

Diet plans you may want to explore include:

Evaluate your treatment plan

You doctor may reevaluate your diabetes treatment plan based on your personal health history and your experiences with hyperglycemia. They may change the amount, type, or timing of your medication.

Don’t adjust your medications without first talking with your doctor or diabetes educator.

Untreated and chronic hyperglycemia can cause both minor and serious complications.

Complications include:

Skin complications

You may experience a variety of skin issues when blood sugar levels are high. For example, your skin may be dry and itchy or you may find skin tags on your groin, armpit, or neck.

Whether you’re diagnosed with diabetes, prediabetes, or you don’t have a diagnosis, you may encounter these skin issues and others, including:

  • Necrobiosis lipoidica. Necrobiosis lipoidica are yellow, red, or brown patches on the skin with small bumps.
  • Acanthosis nigricans. A dark, velvety area of the skin, known as acanthosis nigricans, may form on your groin, armpit, or neck.
  • Digital sclerosis. Digital sclerosis is a hard, thick skin on the fingers or toes. It can spread to other parts of the body, like the knees, ankles, and elbows.
  • Blisters. These can rarely form suddenly but are not painful, according to the American Academy of Dermatology.

Hyperglycemia may make it hard for the body to heal itself, leading to open sores, wounds, ulcers, and skin infections. You may notice these issues particularly on the feet.

Nerve damage

High blood sugar may also lead to diabetic neuropathy, which is a form of nerve damage.

There are four different types:

  • Peripheral. Nerve damage that affects the extremities, including the arms, legs, hands, and feet.
  • Autonomic. Nerve damage that affects the organs, including the eyes, heart, bladder, stomach, and other organs.
  • Proximal. Nerve damage that affects the lower body, such as the thighs, buttocks, and legs, or trunk, such as the stomach and chest.
  • Focal. Nerve damage that affects single nerves in the head, face, torso, hands, or legs.

According to the CDC, damage to the nerves develops slowly and may present as tingling, numbness, weakness, or sensitivity. You may also experience impaired function (for example, bladder leakage) or severe pain.

Eye complications

Hyperglycemia can lead to issues with vision, including blindness, if not addressed promptly. You may not notice any issues with your vision right away, but high blood sugar levels can damage the blood vessels in the eyes, leading to swelling or blurry vision.

Possible issues include:

  • Diabetic retinopathy. With diabetic retinopathy, new blood vessels can form on the back of the eye and affect the retina. The retina is the part of the eye that processes light.
  • Diabetic macular edema. This swelling in the macula, a part of the retina, can lead to issues seeing faces, reading, or driving.
  • Cataracts and glaucoma. Hyperglycemia may also lead to a buildup of deposits on the lens of your eye, which is known as a cataract, or damage to the optic nerve, which is known as glaucoma.


HHS is a rare condition that appears most often in older adults with type 2 diabetes. It may be accompanied by a trigger, such as an illness.

When blood glucose levels are high, the kidneys excrete sugar into the urine, taking water with it. This causes the blood to become more concentrated, resulting in high sodium and blood glucose levels.

Without treatment, HHS may lead to life threatening dehydration and even coma.

A few lifestyle changes may help prevent you from developing hyperglycemia. Try the tips below:

  • Test yourself regularly. Test and record your blood glucose levels on a regular basis each day. Share this information with your doctor at every appointment.
  • Manage your carb intake. Know how many carbohydrates you’re getting with each meal and snack. Strive to stay within the range approved by your doctor or dietitian. Keep this information with the records of your blood glucose levels.
  • Be diabetes smart. Have an action plan for if and when your blood glucose reaches certain levels. Take your medication as prescribed, being consistent about the amount and timing of your meals and snacks.
  • Have alcohol in moderation. Although hypogylcemia is a more likely outcome, drinking large amounts of alcohol can eventually lead to high blood glucose levels. If you’re having alcohol, choose a drink that’s low in carbs and sugar.
  • Wear medical identification. Medical bracelets or necklaces can help alert emergency responders to your diabetes if there’s a greater problem.

Seek immediate medical attention if you experience symptoms of DKA or HHS, like:

  • shortness of breath
  • nausea or vomiting
  • fever
  • confusion
  • dry mouth

Contact a doctor if your blood glucose readings are consistently high, whether in a fasting state or after meals. As well, let your doctor know if their recommended lifestyle measures are not making a difference in your readings.

Make an appointment if you notice new or worsening issues with your vision or skin, or if you suspect you have nerve damage or other health issues that relate to high blood sugar.

To prepare for your appointment:

  • Bring a record of your blood sugar readings that includes when your readings were taken and whether they were taken with or without food.
  • Pay close attention to any instructions a medical professional gives you regarding blood work — you may need to fast.
  • Bring a list of your current medications and supplements, as well as a list of questions to ask your doctor.

You probably won’t feel the effects of hyperglycemia right away. Over time, though, it can cause noticeable symptoms, such as thirstiness and excessive urination.

If the hyperglycemia isn’t properly treated, you can even develop DKA or HHS. Both of these conditions are considered medical emergencies.

Know the symptoms of hyperglycemia and these related conditions, and make it a habit to regularly check your blood glucose levels. Good diabetes management and careful monitoring of your blood glucose levels are both very effective means for preventing hyperglycemia or stopping it before it gets worse.

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