High blood glucose, also known as hyperglycemia, is a condition in which the body has too much sugar in the bloodstream. It typically occurs when someone with diabetes does not use his or her insulin as directed or has an underlying illness that affects their insulin levels. Other factors that may cause blood glucose levels to rise include stress, eating sugary foods or carbohydrates, skipping meals, not being physically active, certain medications, and certain medical conditions.

The consequences of high blood glucose include: dehydration, fatigue, headaches and mood swings. Long-term health effects include damage to the kidneys and nerves, the development of cardiovascular disease and stroke, coma and even death. High blood sugar can also cause increased hunger sensations and increased urination leading to an increased risk of dehydration. In some cases it can lead to blurred vision and nerve problems due to damaged blood vessels in the eyes and feet that can result in amputation if left untreated.