If an individual records a fasting, or before meal, blood sugar level of 300 or higher, she is likely in medical danger and needs to contact her doctor immediately, states the University of Washington's Women's Health Center. Patients with fasting blood glucose levels this high are at risk for kidney, eye and nerve damage.
A fasting blood glucose test performed by a medical professional is measured in milligrams of glucose per deciliter of blood, and any result over 126 milligrams per deciliter is an indicator of diabetes, according to MedlinePlus. Normal results of a fasting blood glucose test are in the 70 to 100 milligrams per deciliter range. Other medical conditions that can result in higher than normal fasting blood glucose test results include thyroid and pancreatic disorders, several types of rare tumors, or stress from surgery or cardiac events, states MedlinePlus.
To definitively diagnose diabetes, two separate overnight blood glucose fasting tests must show results above the 126 milligrams per deciliter range, reports the Mayo Clinic. The test checks for type 1 and type 2 diabetes as well as prediabetes, and unusually high results often indicate a need for further testing to determine the type of diabetes suspected and to rule out other conditions.