Hyperglycemia means that the sugar (glucose) level in the blood is too high. In theory, hyperglycemia is defined as a fasting glucose level above 6.1 mmol/l or 110 mg/l. In its initial stages, hyperglycemia has no symptoms. That’s why it’s important to monitor blood sugar regularly. When hyperglycemia persists, it can cause various symptoms such as fatigue, thirst, a dry sensation in the mouth or excessive urination.