Symptoms of high blood glucose levels may be, moderate, or severe. High blood sugar (hyperglycemia) is most often seen in people who have diabetes that is not well controlled.

What is a high blood sugar level?

Blood glucose is considered very high when it is greater than 130 mg/dL before a meal or higher than 180 mg/dl two hours after the first bite of a meal.

However, most symptoms do not appear until the blood glucose level is higher than 250 mg/dL.

Some of the symptoms start quickly, while others require a long period of high blood glucose to be detected.

It is important to know that people have different effects of high blood sugar. Some feel symptoms faster or stronger than others; each symptom has a biological basis or a specific cause.

Hyperglycemia can be acute or chronic. Acute, brief and often is the result of a high-carb meal or a forgotten dose of medication, among others.

Chronic hyperglycemia, on the other hand, is a long-term state of high blood glucose. It is often the result of diabetes that has not been diagnosed or an inadequate diabetes treatment regimen.

Symptoms of high blood glucose levels: Slightly high blood sugar

If your blood sugar levels are continuously above your ideal limits (usually 200 milligrams per deciliter(mg/dL)to 350 mg/dL in adults and 200 mg/dL  to 240 mg/dL  in children), you may have mild symptoms of high blood sugar. You may urinate more than usual if you are drinking enough fluids.

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Some people who have diabetes may not notice any symptoms when their blood sugar level is at this level. The main symptoms of high  blood sugar include:

    Increased thirst.

    Increased urination.

    Weight loss.


    Increased appetite.

Young children are not able to recognize symptoms of high  blood sugar. Parents have to give their child a home blood sugar test every time they suspect hyperglycemia.

If you don’t drink enough fluids to replenish fluids lost to high blood sugar levels, you may become dehydrated. Young children can become dehydrated very quickly. Symptoms of dehydration include:

    Dry mouth and increased thirst.

    Warm, dry skin.

Symptoms of high blood glucose levels: Moderate to severely high blood sugar

If your blood sugar levels are continuously high (usually above 350mg/dL  in adults and above 240 mg/dL  in children), you may have moderate to severe symptoms of high blood sugar. These symptoms include:

    Blurred view.

    Sed extrema.


    Red, hot and dry skin.

    Agitation, drowsiness or difficulty waking up.

If your body produces little or no insulin (individuals with type 1 diabetes and some people with type 2diabetes), you may also have:

    Fast and deep breathing.

    Rapid heart rate and weak pulse.

    Breath with strong and fruity smell.

    Loss of appetite, abdominal pain and vomiting.

If your blood sugar levels keep rising, it may become confusing and lethargic. You may also lose consciousness if your blood sugar levels go up a lot.

Causes of hyperglycemia

You may experience an increase in your blood sugar level as a result of:

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    Have forgotten the administration of insulin or made an error in the technique of injecting it.

    Have ingested foods or beverages high in carbohydrates: queues, juices, smoothies, pastries, cakes, ice cream, chocolate, etc., or taken more than usual of fruit, pasta, potatoes, legumes, rice, bread or milk without having adequated the dose of rapid insulin.

    Having an infection. It is the most common cause of hyperglycemia and diabetes decompensation. When you have an infection (cold, dental phlegmon, urine infection…) your body raises the production of certain hormones to fight it. This causes your blood sugar to rise. For this reason, if you feel sick, it is very important that you see your doctor as soon as possible.

    Taking other medications. Some drugs, such as corticosteroids, can cause hyperglycemia. It’s very important to check with your doctor whenever you’re prescribed a new medicine.

    Not having adapted treatment if you need to give yourself insulin. If this is the case, you should adjust your insulin pattern and dose frequently.

When is your blood sugar level dangerous?

“Fasting, the normal blood sugar level is 70 to 110 milligrams per deciliter (mg/dL). After meals, these values go up, but insulin gets back to the normal range quickly (usually 2 hours). Values greater than 180 mg/dL sustained for more than 2 hours are toxic to cells, and repeating them can often cause permanent damage to them, especially in kidneys, eyes, heart and nerves in the legs.”

Blood Glucose Table
CategoryFasting Values (mg/dl)Post Prandial (mg/dl)
Minimum ValuesMaximum ValuesValues 2 hours after glucose consumption
Normal70100< 140
Early Diabetes101126140 to 200
Diabetes Established> 126> 200
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