Blood Sugar Diabetes & Impaired Glucose Tolerance Levels

Diabetes mellitus (type 2 diabetes), also known commonly as sugar diabetes, is the inability of the body to maintain the blood sugar levels within a normal range. Prior to the onset of sugar diabetes, a state known as impaired glucose tolerance (IGT) or pre-diabetes, exists whereby the fluctuating blood glucose levels may not reach extreme levels as in diabetes mellitus. In pre-diabetes, the body’s mechanisms for maintaining normal blood glucose levels is still functioning, although impaired.

What is Insulin Resistance & Pre-Diabetes?

Upon consuming foods, particularly carbohydrates,  the digestive system along with the liver, break down the food into simple sugars like glucose. Glucose then enters the blood stream where it is transported to cells throughout the body. Excess glucose is converted to glycogen and stored in the liver and muscles. Any remaining glucose may be converted for fat storage. This blood glucose regulating mechanism is primarily controlled by the hormone, insulin, which is secreted by the pancreas (beta cells in the islets of Langerhan’s).

Insulin triggers cells to take up glucose from the blood so that individual cells can burn this glucose for energy. Alternatively, excess glucose is converted into glycogen and stored in the liver due to the action of insulin. In insulin resistance, seen in impaired glucose tolerance (or pre-diabetes), the body’s cells and liver do not respond to insulin. Excess glucose builds up in the blood stream and the pancreas attempts to secrete more insulin. This excess insulin secretion may not always trigger the desired effect resulting higher than normal blood glucose levels.

Over time, insulin resistance and pre-diabetes will lead to type 2 diabetes, also known as adult-onset diabetes or non-insulin dependent diabetes.

Blood Glucose Levels in Pre-Diabetes & Sugar Diabetes

While the symptoms of diabetes may give an indication of the condition, along with the presence of risk factors, measuring the blood glucose levels is necessary for a conclusive diagnosis. In certain conditions, where only primary health care facilities are available, a finger-prick or blood drop test may be conducted to verify the blood glucose levels. This should not be used for the diagnosis of pre-diabetes (impaired glucose tolerance) or type 2 diabetes (sugar diabetes).  As far as possible, a plasma glucose test should be done to verify the glucose tolerance.

This can be done by testing the fasting glucose levels (fasting plasma glucose test), where a patient’s blood is withdrawn in the morning before breakfast, usually a minimum of  8 hours after the last meal. Another option is the oral glucose tolerance test (OGTT) where a fasting plasma sample is first taken. The patient is then administered a metered dose of a glucose solution orally. A second blood sample is taken 2 hours after consuming the glucose solution. In cases where gestational diabetes (diabetes during pregnancy) is suspected, an intermediate blood sample is taken, usually one hour after the glucose solution is administered. A fourth sample may be taken 3 hours after the glucose  solution administration, depending on the quantity of glucose used within the solution.

Normal Fasting Plasma Glucose Levels

Reading = 70 mg/dL to 99mg/dL (3.9 mmol/L to 5.5 mmol/L)

High Fasting Glucose Levels indicative of Impaired Glucose Tolerance/Pre-Diabetes

Reading = 100 mg/DL to 125 mg/DL (5.6 mmol/dL to 6.9 mmol/L) *

High Fasting Glucose Levels indicative of Type 2 Diabetes

Reading = 126mg/DL (6.8 mmol/L) or above. *

Normal Glucose Levels after 1 hour (OGTT)

Reading = Less than 140 mg/dL (7.8 mmol/L)

High 1 hour Glucose Levels (OGTT) indicative of Impaired Glucose Tolerance/Pre-Diabetes

Reading = 140 mg/DL to 200 mg/DL (7.8 mmol/dL to 11.1 mmol/L) *

High 1 hour Glucose Levels (OGTT) indicative of Type 2 Diabetes

Reading = Greater than  200 mg/DL (11.1 mmol/L)  *

* Indicates type 2 diabetes but diagnosis should only be confirmed upon a second test.

Glucose Levels indicative of Gestational Diabetes

Fasting Reading > 95 mg/dL (5.3 mmol/L)

One Hour Reading > 180 mg/dL (10 mmol/L)

Two Hour Reading > 155 mg/dL (8.6 mmol/L)

Three Hour Reading > 140 mg/dL (7.8 mmol/L)


  1. Insulin Resistance & Pre-Diabetes. National Diabetes Information Clearinghouse
  2. Glucose Tests. Lab Tests Online

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