Diagnosis of Diabetes 

Early diagnosis of diabetes is crucial in order to prevent its complications. Since the early stages of diabetes don’t usually cause any symptoms, diagnosis is often delayed until complications of diabetes are present, most of which are not reversible.   

So, the earlier you get a diagnosis, the better. However, that also means you need to look for diabetes and not wait until it blindsides you with a heart attack or a stroke.


Those at Risk for Developing Diabetes        

People with the following characteristics are at high risk for developing Type 2 diabetes and therefore, should undergo testing for diabetes even if they have no symptoms. Remember, diabetes is a silent killer.    

1.  Age over 40 years.  

2.  Family history of diabetes, high blood pressure, cholesterol

     disorder,heart attack or stroke.  

3.  Overweight, especially in the abdominal area (waistline more

      than 35 inches in females and 38 inches in males. For

      Asians, these numbers are 32 inches in females and

      35 inches in males).  

4.  High blood pressure (blood pressure greater than 130/85 mm

      Hg, even in a physician’s office).  

5.  Triglyceride level greater than 150 mg/dl.  

6.  HDL cholesterol less than 40 mg/dl. in males and less than

      50 mg/dl in females.  

7.  History of heart attack, angioplasty, stent placement or

      heart  bypass surgery.  

8.  History of Stroke, mini-strokes or dementia. 

9.  History of gestational diabetes or delivery of a baby over

      nine pounds. 

10. Women with a history of irregular menses, excessive hair

      growth or facial acne.  


The Best Test for the Diagnosis of Diabetes  

The tests used to diagnose diabetes are: 

1. Fasting Blood Glucose  

Usually this is done as part of a routine blood test after you have fasted overnight.   

A Fasting Blood Glucose greater than 125 mg/dl = Diabetes. 

A Fasting Blood Glucose between 100 mg/dl to 125 mg/dl = Impaired Fasting Glucose (IFG).  

Impaired Fasting Glucose (IFG) means that you have pre-diabetes and need further testing with an Oral Glucose Tolerance Test. 


2. Oral Glucose Tolerance Test (OGTT) 

The best test to diagnose diabetes is an Oral Glucose Tolerance Test. After an overnight fast, a blood test is drawn for glucose. Then, you are given a  drink containing 75 grams of glucose. Another blood test is drawn at one hour and then again at two hours. You do not eat or drink anything else during this two hour period.

Blood  Glucose at 2 Hours: 

Greater than 200 mg/dl = Diabetes 

Between 140 mg/dl & 200 mg/dl = Impaired Glucose Tolerance (IGT)

Between 100 mg/dl & 140 mg/dl = Mild Glucose Intolerance  

In normal people, the value should come back to near baseline after 2 hours. For example, if your fasting blood glucose was 95 mg/dl, then two hours after drinking the 75 grams of glucose, it should come back to about 95 mg/dl. 

The 2-hour Oral Glucose Tolerance Test (OGTT) has been the international  standard to diagnose diabetes for a long time. Most scientific studies about diabetes utilize it as THE diagnostic test.  

Several excellent scientific studies have demonstrated that the Oral Glucose  Tolerance Test is a superior test for diagnosing diabetes as compared to the fasting blood glucose test.  



Please pay attention to the units in which your blood glucose is reported by the laboratory. In the U.S.A., blood glucose is reported as mg/dl. But in many parts of the world, it is reported as mmol/L.  

The conversion factor from mmol/L to mg/dl is 18. For example:  

1 mmol/L = 18 mg/dl 

7 mmol/L = 126 mg/dl 

7.8 mmol/L =140 mg/dl 

11.1 mmol/L = 200 mg/dl    


 For more details, please refer to Dr. Zaidi's book, "Take Charge of Your Diabetes."



This article was written by Sarfraz Zaidi, MD, FACE. Dr. Zaidi specializes in Diabetes, photoEndocrinology and Metabolism.

Dr. Zaidi is a former assistant Clinical Professor of Medicine at UCLA and Director of the Jamila Diabetes and Endocrine Medical Center in Thousand Oaks, California.


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