Hyperglycemia is a condition in which an excessive amount of glucose circulates in the blood plasma. This is generally a blood sugar level higher than 11.1 mmol/L (200 mg/dL), but symptoms may not start to become noticeable until even higher values such as 13.9¨C16.7 mmol/L (~250¨C300 mg/dL). A subject with a consistent fasting blood glucose range between ~5.6 and ~7 mmol/L (100¨C126 mg/dL) (American Diabetes Association guidelines) is considered slightly hyperglycemic, and above 7 mmol/L (126 mg/dL) is generally held to have diabetes. For diabetics, glucose levels that are considered to be too hyperglycemic can vary from person to person, mainly due to the person's renal threshold of glucose and overall glucose tolerance. On average, however, chronic levels above 10¨C12 mmol/L (180¨C216 mg/dL) can produce noticeable organ damage over time.

Reference
Wiki: Hyperglycemia