Prior to developing type 2 diabetes, most people develop a condition called pre-diabetes.  This is where a person’s blood glucose levels are higher than normal but not as high as with diabetes. Many times there are no signs or symptoms to help recognize that there is a problem. People with pre-diabetes, approximately 79 million Americans, or 35 percent of U.S. adults, face an increased risk of developing type 2 diabetes within a decade. Unless adult Americans change their eating habits and get more exercise, type 2 diabetes will be among the most prominent preventable diseases. Research suggests that pre-diabetes may cause some damage to the body, especially the heart and circulatory system. People with pre-diabetes have a greater stroke risk as well.

Diabetes is a progressive disease, and once diagnosed with pre-diabetes, it may take years to develop into diabetes. Insulin is produced and stored in the beta cells. During the time before overt detection and diagnosis of diabetes, the pancreas may produce more insulin but the insulin is not as effective as it once was. The blood glucose rises due to the insulin not working properly. This is a condition known as insulin resistance. This is thought to be caused by impaired or altered beta cell function. Over time as diabetes progresses, destruction of beta cells may occur without the body replacing some of these cells. Pre-diabetes is defined as fasting blood glucose of 100-125mg/dl, or HgA1c of 5.7-6.4 percent. People with pre-diabetes often have a higher than normal blood glucose 1-2 hours after eating a meal of between 140-199 mg/dl. Routine yearly blood tests can screen for pre-diabetes. Patients may be able to stop the progression from pre-diabetes into type 2 diabetes by losing at least 7 percent of body weight, eating a balanced diet and exercising 30 or more minutes, at least five times per week.

Detecting Diabetes

There are several tests that may be used to make a diabetes diagnosis. Depending on the outcome of these tests, a patient could be categorized as: not having diabetes (normal blood glucose range), pre-diabetes, gestational diabetes (women who develop diabetes during pregnancy), or overt diabetes. The doctor can also test to determine if diabetes is type 1 or 2.

Fasting plasma glucose test (FPG)

Your blood glucose value after fasting for at least 8 hours. Water is the only food or beverage allowed during the fast.

Oral glucose tolerance test (OGTT)

Your blood glucose is measured fasting and then 2 hours after drinking a beverage made with a premeasured amount of glucose.

Glycated Hemoglobin Test (Hemoglobin A1c or HbA1c)

A blood test that measures average blood glucose over the past two to three months. IWhen hemoglobin combines in the body with glucose a substance called a glycosylated hemoglobin or hemoglobin A1c is made. This test measures the percentage of this substance. Normal amounts are less than 5.7 percent.

C-peptide test

A blood test to measure the level C-peptide in your blood. In your pancreas, before insulin is released it is actually a compound made of both insulin and c-peptide known as pro-insulin. Very little pro-insulin is secreted into the bloodstream from the pancreas intact.  When the pancreas releases insulin, it releases c peptide as well.  C-peptide is generally equal to the amount of insulin in your blood. This test is generally used when a patient is first diagnosed with diabetes to determine whether they have type 1 or type 2 diabetes. People with type 1 diabetes have little or low levels of insulin and thus low levels of c-peptide. People with type 2 diabetes may have normal or high levels of c-peptide.

Blood Glucose Target Ranges and Diagnosis

Blood glucose target ranges vary between organizations that have recommendations. The following values are based on the American Diabetes Association posted guidelines.

Normal Blood Glucose Targets

  • HbA1c – less than 5.7 percent
  • Fasting Plasma Glucose – less than 100mg/dl
  • Oral Glucose Tolerance Test – less than 140 mg/dl

Pre-Diabetes Diagnosis

  • HbA1c – equal to or greater than 5.7 percent, but less than 6.5 percent
  • Fasting Plasma Glucose –equal to or greater than 100 mg/dl, but less than 126 mg/dl
  • Oral Glucose Tolerance Test – equal to or greater than 140 mg/dl, but less than 200 mg/dl

Diabetes Diagnosis

HbA1c – equal to or greater than 6.5 percent (on two separate occasions)
Fasting Plasma Glucose – equal to or greater than 126 mg/dl (on two separate occasions)
Oral Glucose Tolerance Test – equal to or greater than 200 mg/dl (on two separate occasions)
Random Blood Glucose – greater than 200 mg/dl and symptoms present at any time during the day

Gestational Diagnosis

Screen women with risk factors for type 2 diabetes at the first pre-natal visit using the criteria mentioned under diagnosing diabetes. A woman could possibly be diagnosed with type 2 diabetes at this time. A woman without risk factors for diabetes is usually screened at 24-28 weeks of gestation for gestational diabetes. The 2014 recommendations are as follows:


  • Perform a 50-g GLT (non-fasting), with plasma glucose measurement at 1 h (Step 1), at 24–28 weeks of gestation in women not previously diagnosed with overt diabetes
  • If the plasma glucose level measured 1 h after the load is ≥140 mg/dL* (7.8 mmol/L), proceed to 100-g OGTT (Step 2); the 100-g OGTT should be performed when the patient is fasting
  • The diagnosis of GDM is made when the plasma glucose level measured 3 h after the test is ≥140 mg/dL (7.8 mmol/L).