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 don't have diabetes. Depending on what you eat and drink, 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. “Millimoles per liter” (mmol/L) is the international unit for measuring blood sugar. It describes the amount of a certain substance per liter.

Blood sugar levels are considered to be too high (hyperglycemia) if they are above 7.8 mmol/L (140 mg/dL). When someone develops hyperglycemia, it is usually because they don't have enough insulin or because their insulin doesn't work properly. Without insulin, the organs in the body can't use the sugar in the blood properly. As a result, sugar builds up in the blood. If type 1 diabetes is left untreated, blood sugar levels can increase to over 27.8 mmol/L (500 mg/dL). Such high levels tend to be uncommon in type 2 diabetes.

Blood sugar concentrations below 3.3 mmol/L (60 mg/dL) are considered to be too low (hypoglycemia). As you can see in the illustration below, there are no clear-cut borders between the normal range of blood sugar and abnormal (too high and too low) blood sugar.

Blood sugar: Normal range between hyperglycemia and hypoglycemia

Signs of hyperglycemia

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

• Extreme thirst, drinking a lot, and then frequent urination (peeing often) as a result
• Losing a lot of weight within a few weeks although you're not trying to
• Noticeable loss of energy with muscle weakness, tiredness and generally feeling very unwell
• Nausea and stomach pain
• Vision problems
• Poor concentration
• Frequent infections (cystitis, thrush)

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 or your child have any of the above symptoms, you should seek medical advice from a doctor. They can adjust the medication to reduce the blood sugar levels again. A stay at the hospital might be a good idea while the blood sugar levels are being stabilized.

Important: If symptoms such as drowsiness, confusion or loss of consciousness occur, 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 unexpected physical activity, eating too little, 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
• Headaches
• 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're not sure whether your blood sugar is too low, you can measure it to make sure.

Blood sugar levels can drop at night too, leaving you feeling groggy and weak when you wake up in the morning.

Mild hypoglycemia doesn't usually have any harmful effects. But severe hypoglycemia can make you lose consciousness and become life-threatening.

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

It is important to react immediately and eat or drink something, such as dextrose sugar or sugary drinks (no "diet" or "zero" drinks with artificial sweeteners!).

To avoid severe hypoglycemia, people who have type 1 diabetes often carry a pre-filled pen or syringe on them containing glucagon. This hormone makes the liver release sugar into the bloodstream.

If the person who has diabetes can't inject it themselves, others can do it for them. Otherwise it's important to immediately call the emergency services (112 in Germany and many other countries, 911 in the U.S.) and ask for medical help.

If blood sugar levels keep dropping too low, it's important to talk to your doctor about it. They may then adjust your medication or recommend making lifestyle changes.

Sources

• Deutsche Diabetes Gesellschaft (DDG). Diagnostik, Therapie und Verlaufskontrolle des Diabetes mellitus im Kindes- und Jugendalter (S3-Leitlinie). AWMF-Registernr.: 057-016. 2015.
• Deutsche Diabetes Gesellschaft (DDG). S3-Leitlinie: Therapie des Typ-1-Diabetes. AWMF-Registernr.: 057-013. 2018.

• 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.

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