Hyperglycemia and hypoglycemia in type 1 diabetes

Photo of a woman with a glass of water
PantherMedia / Sven Weber

Hyperglycemia occurs when blood sugar levels are too high. People develop hyperglycemia if their diabetes is not treated properly. Hypoglycemia sets in when blood sugar levels are too low. This is usually a side effect of treatment with blood-sugar-lowering medication.

Diabetes is a metabolic disease with far-reaching health effects. In type 1 diabetes, the body only produces very little insulin, or none at all. In type 2 diabetes, not enough insulin is released into the bloodstream, or the insulin cannot be used properly.

We need insulin to live. Without it, sugar (glucose) builds up in the blood because it cannot be taken out and used by the body. Very high blood sugar, known as hyperglycemia, leads to a number of symptoms. If blood sugar levels are too low, it is called hypoglycemia.

When is blood sugar considered to be too high or too low?

Slight fluctuations in blood sugar levels are completely normal and also happen on a daily basis in people who do not have diabetes. Between around 60 and 140 milligrams of sugar per deciliter of blood (mg/dL) is considered to be healthy. This is equivalent to blood sugar concentrations between 3.3 and 7.8 mmol/L. “Millimole per liter” (mmol/L) is the international unit for measuring blood sugar. It indicates the concentration of a certain substance per liter.

If type 1 diabetes is left untreated, people’s blood sugar levels can get very high, sometimes exceeding 27.8 mmol/L (500 mg/dL). Blood sugar concentrations below 3.3 mmol/L (60 mg/dL) are considered to be too low. As you can see in the illustration below, there are no clear-cut borders between the normal range of blood sugar and high and low blood sugar. 

Illustration: Normal range of blood sugar between hyperglycemia and hypoglycemia

Blood sugar: Normal range between hyperglycemia and hypoglycemia

Signs of hyperglycemia

Signs of very high blood sugar levels in type 1 diabetes may include the following:

  • Extreme thirst, drinking a lot and then urinating frequently as a result
  • Unintentionally losing a lot of weight within a few weeks
  • Noticeable loss of energy with muscle weakness, tiredness and generally feeling quite unwell
  • Nausea and stomach ache
  • Trouble seeing
  • Poor concentration
  • Frequent infections (cystitis, thrush)
  • Confusion and drowsiness, or even coma

If you or your child have these symptoms, you should see a doctor as soon as you can.

Signs of hypoglycemia

Low blood sugar is most common in people who use insulin or take certain tablets to reduce high blood sugar. This is because things like unplanned physical activity, eating meals later than usual, or drinking too much alcohol can mean that you need less insulin than you thought, causing your blood sugar to drop very low.

Signs that your blood sugar is too low may include:

  • Racing pulse
  • Cold sweats
  • Pale face
  • Headache
  • Feeling incredibly hungry
  • Shivering, feeling weak in the knees
  • Feeling restless, nervous or anxious
  • Difficulty concentrating, confusion

These symptoms do not occur all at once. The signs of hypoglycemia not only depend on the blood sugar level, but also vary from person to person. If you are not sure whether your blood sugar is too low, you can measure it to make sure. Mild hypoglycemia doesn't usually have any harmful effects. But it is important to react quickly enough and eat or drink something, such as dextrose sugar or sugary lemonade.

People who have severe hypoglycemia may feel very drowsy and confused, and might even become unconscious. If this happens, someone else can inject the hormone glucagon. If this is not possible it is important to call the emergency services (in Germany and many other countries: 112, in the United States: 911) immediately and ask for medical help.

Deutsche Diabetes Gesellschaft e.V. (DDG). Diagnostik, Therapie und Verlaufskontrolle des Diabetes mellitus im Kindes- und Jugendalter. S3-Leitlinie. October, 2015. (AWMF-Leitlinien; volume 057 - 016).

Deutsche Diabetes Gesellschaft e.V. (DDG). Therapie des Typ-1-Diabetes. S3-Leitlinie. September 2011. (AWMF-Leitlinien; volume 057 - 013).

Leelarathna L, Guzder R, Muralidhara K, Evans ML. Diabetes: glycaemic control in type 1. BMJ Clin Evid 2011.

IQWiG health information is written with the aim of helping people understand the advantages and disadvantages of the main treatment options and health care services.

Because IQWiG is a German institute, some of the information provided here is specific to the German health care system. The suitability of any of the described options in an individual case can be determined by talking to a doctor. informedhealth.org can provide support for talks with doctors and other medical professionals, but cannot replace them. We do not offer individual consultations.

Our information is based on the results of good-quality studies. It is written by a team of health care professionals, scientists and editors, and reviewed by external experts. You can find a detailed description of how our health information is produced and updated in our methods.

Comment on this page

What would you like to share with us?

We welcome any feedback and ideas. We will review, but not publish, your ratings and comments. Your information will of course be treated confidentially. Fields marked with an asterisk (*) are required fields.

Please note that we do not provide individual advice on matters of health. You can read about where to find help and support in Germany in our information “How can I find self-help groups and information centers?

Updated on June 29, 2017
Next planned update: 2021


Institute for Quality and Efficiency in Health Care (IQWiG, Germany)

How we keep you informed

Follow us on Twitter or subscribe to our newsletter or newsfeed. You can find all of our films online on YouTube.