A blood sugar level of more than 150 to 200 milligrams per deciliter of blood (mg/dl) usually is high enough to cause symptoms.

When your blood sugar is high, some of the sugar "overflows" through your kidneys into your urine. Fluid goes with it. This means you make more urine than normal. For this reason, high blood sugar leads to dehydration. Sometimes dehydration from high blood sugar is severe. It can require a hospital stay. You may need to get fluids through a vein (intravenous).

Symptoms of too much urine production due to a high blood sugar include:

• Frequent urination
• Thirst

When sugar flows out in urine, your body loses an important fuel. This loss of sugar (and the calories it contains) can cause the following symptoms:

• An unusually strong appetite
• Weight loss even though you may eat a lot

High sugar levels in the blood and in some tissues can affect the water content in different areas of your body. Water may soak into some tissues and seep out of others in unusual ways. As a result, some of the cells and structures in the body may not function perfectly. Problems that result can include:

• Weakness of the immune system
• Blurred vision from temporary swelling and shrinking of the lens in your eye
• (In severe cases) sudden brain problems, including:
  
  • Confusion
  • Stroke symptoms
  • Seizure
  • Coma (known as hyperosmolar syndrome)

When your blood sugar is high, it is usually a sign that your tissues can't easily pull sugar out of your bloodstream to use for energy. This "sugar-hunger" in your body tissues can cause:

• Weakness
• Fatigue
• (Rarely) substitution of other body fuels, especially "ketones," which can cause a body acid imbalance. This problem is called ketoacidosis. It is quite unusual in type 2 diabetics but is dangerous when it does occur.

Yeast and fungus commonly found on body surfaces grow best when blood sugar is high. This can lead to yeast and fungal infections. Examples include:

All of these symptoms can be relieved with treatment that controls high blood sugar. If the blood sugar levels stay high for long periods, then later health problems are very likely to develop.