The level of sugar in the blood varies, and your blood sugar levels will generally soar after you eat a meal. This is why blood sugar levels are tested in individuals before they have their food. Diagnosticians normally test a person's blood sugar levels before breakfast, as blood sugar levels will take more than six hours (after a meal) to return to normal levels. The normal level of blood sugar is around 70 to 100 mg per deciliter of blood. After a meal, blood sugar levels can increase to levels of 135 mg per deciliter of blood. The kidneys stop absorbing the glucose if blood sugar levels rise beyond the 180-200 mark.