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Hyperglycemia and hypoglycemia in type 2 diabetes

Created: ; Last Update: January 11, 2018; Next update: 2021.

If someone has diabetes that isn’t treated properly, they have too much sugar in their blood (hyperglycemia). Too little sugar in the bloodstream (hypoglycemia) is usually a side effect of treatment with blood-sugar-lowering medication.

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

We need insulin to live. Without it, sugar (glucose) builds up in the blood because it can’t 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 every day in people who don’t have diabetes, in response to the food they eat. Between around 60 and 140 milligrams of sugar per deciliter of blood (mg/dL) is considered to be healthy. This is equivalent to a blood sugar concentration of between 3.3 and 7.8 mmol/L. “Millimole per liter” (mmol/L) is the international unit for measuring blood sugar. It indicates the amount of a certain substance per liter.

If type 1 diabetes is left untreated, people’s blood sugar levels can get very high, even exceeding 27.8 mmol/L (500 mg/dL). Such high levels tend to be uncommon in type 2 diabetes, though. 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: Blood sugar: Normal range between hyperglycemia and hypoglycemia, as described in the article

Blood sugar: Normal range between hyperglycemia and hypoglycemia

Signs of hyperglycemia

People with type 2 diabetes don’t always realize that their blood sugar is too high. The condition can develop gradually over many years without causing any noticeable symptoms. But very high blood sugar can cause the following symptoms:

  • Extreme thirst
  • Frequent urination
  • Feeling tired
  • Listlessness
  • Nausea
  • Dizziness

If someone has extremely high blood sugar levels, they may feel confused and drowsy or even lose consciousness (diabetic coma).

What can you do if your blood sugar levels are too high?

If you notice that your blood sugar is too high based on the above symptoms, it's important to see a doctor. Then your medication can be adjusted to make your blood sugar levels go back down. A stay at the hospital might be a good idea while the blood sugar levels are being stabilized. If you are feeling drowsy, confused or lose consciousness, the emergency services should be called (112 in Germany and many other countries, 911 in the U.S.).

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

The severity of these symptoms depends on the blood sugar level and varies from person to person. The symptoms don’t occur all at once. If you aren’t sure whether your blood sugar is too low, you can measure it to make sure. Mild hypoglycemia doesn’t usually have any harmful effects.

What can you do if your blood sugar levels are too low?

It is important to react quickly enough and eat or drink something, like dextrose sugar or a sugary drink (with sugar, not artificial sweeteners!).

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 U.S.: 911) immediately and ask for medical help.


  • Bundesärztekammer (BÄK), Kassenärztliche Bundesvereinigung (KBV), Arbeitsgemeinschaft der Wissenschaftlichen Medizinischen Fachgesellschaften (AWMF). Nationale Versorgungsleitlinie: Therapie des Typ-2-Diabetes (S3). AWMF-Registernr.: nvl-001g. November 2014.
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