How High Is Too High for a Blood Sugar Reading, and What Are the Dangers?

A high blood sugar level is defined as a reading of greater than 130 mg/dL after 8 hours of fasting or a reading of greater than 180 mg/dLafter eating a meal, according to WebMD. Frequent high blood sugar can cause damage to the nerves, blood vessels and other organs.

Although diabetes is the most common reason for high blood sugar, there are many other causes, such as infection, injury or even just eating more sugar than normal, notes MedicineNet. When symptoms such as increased thirst, increased urination and weight loss accompany high blood sugar, diabetes is diagnosed, states WebMD.

High blood sugar coats blood cells, which in turn causes the cells to hinder circulation, explains the Mayo Clinic. The small blood vessels are particularly susceptible to these problems, so damage to the eyes, kidneys and feet are common in those with chronically high blood sugar. Controlling high blood sugar can prevent or lessen complications such as heart attack, stroke, eye damage that can lead to blindness, nerve damage in the hands and feet, kidney damage, gum disease and tooth loss. Damage can begin when blood sugar is higher than normal, but not high enough to be considered diabetes. Increasing physical activity and losing weight can help decrease blood sugar in people who are at risk for developing diabetes.