For diagnosis, blood sugar levels are measured by pricking the skin with a home device available through your local pharmacy (or on the internet) or having a blood sample drawn by a phlebotomist or other health care professional. Although lab references ranges for fasting glucose vary by lab, I typically look for glucose values under 100. Fasting means 12 hours without food. Values between 100 and 120 typically indicate some levels of insulin resistance. More than one sample is typically taken over time, to make an accurate diagnosis. Hemoglobin A1c is the best measure for longer term management of blood sugars, once insulin resistance or diabetes has been diagnosed. For other aspects of blood sugar disregulation, the GTT is often performed. A specific amount of glucose is ingested, and blood samples are taken each hour for 1-4 hours after ingesting the glucose. This is often the best way to assess irregular patterns of insulin release. So, the short answer to your question is --it depends whether the blood sugar levels are for diagnosis or for on-going management of an existing condition. Many websites and books have been devoted to diabetes managment, and offer good information for those who are managing an existing condition.
answered by Dr K B N