Glucose Tests and Diabetes

If there is one biological substance associated with diabetes, besides insulin, it is glucose. Knowing your glucose levels are of supreme importance to knowing how controlled or out-of-control, your diabetes is at any time.


Times have changed thanks to technology. The testing methods for determining that all important blood sugar level has changed along with the discovery of easier and more exact ways of detecting and recording sugar levels. This is applicable to both urine and blood tests. Today, you can find proprietary sticks or tapes, referred to as dipsticks, for fast testing of urine. They are simple to use, convenient and fairly reliable. There are also glucose meters requiring a quick prick of the finger and tapes that “read” your blood sugar content.

Test results are positive if there is a substantial quantity of sugar in the urine or blood. However, the use of home sticks and tapes for testing is limited. They are best in application for screening of a very general natural. If there is any question about the results or doubts about whether it is a true positive, further testing is needed. This should take place in a suitable clinical laboratory where the standards have been certified by the right authorities.

Once an individual has been diagnosed with diabetes, the doctor will arrange for a series of tests. These usually first require one sample of urine and one of blood.

Using Blood to Test for Glucose

The test may be one of two types. It can be either

  • Random sample – This is also called a casual blood sugar sample. Its name refers to the test being done at random. There is no consideration given as to when you ate your last meal or what you ate.[1]
  • Fasting sample – this requires advance preparation. It can be inconvenient because the individual must not eat or drink anything containing calories at least 8 hours prior to taking the test.

Whatever type of test is administered, when it is done by a doctor the process is as follows.

  • A needle is placed in a vein in the arm to draw out venous or dark blood
  • The blood is then taken to a laboratory to be analyzed
  • The test is performed on the serum, not the whole blood. Serum is what remains following the spinning off of the red and white cells as well as other matter.

The result of the test may be “normal.” This actually refers to what is considered as average. Statistics indicate that the vast majority of individuals, when tested, had a blood sugar level characterized as always lying beneath a specific point. This, however, occurred only under specific conditions. The result was a standardization of the testing methods or test and the institution of specific standards of testing blood sugar.

Measurements have been adapted for each country. In the United States, for example, the measurement appears as milligrams of whatever substance per deciliter. A deciliter is 100 cubic centimeters, or milliliters. The result is so many mg/dl. In the United States, therefore, the normal fasting blood sugar level is below 126 mg/dl. In Canada and elsewhere where the metric system is used, the system is different. It is in mmols. As a result, the normal blood sugar level is expressed as 11.1 mmol/l.

It is important to keep this in mind if you travel. If you visit a doctor be sure to notify him or her of the difference in measurement readings. The same thing is true if the doctor is reading a patient’s results from another country or looking at a report from a country which uses the metric system.

Another way to diagnose diabetes using the blood glucose test is to combine the results of the test with clinical symptoms. If a person has a random glucose level greater than 200 mg/dl and symtpoms of diabetes, they are considered to be diabetic. Symptoms can include increased thirst (polydypsia), increased urination (polyuria), weight loss, blurry vision, and fatigue.

What the Numbers mean

When the numbers are too low or too high, you will require further testing and examination. Fasting glucose normal levels are usually between 60 and 110 mg/dl levels for those without diabetes. This is during the morning. A random blood sugar test will be different. This is because the glucose levels change after meals. They rise in response to the glucose that has entered into the blood stream. The norm during this period can rise as high as 150 mg/dl with an acceptable range being between 80 to 180 mg/dl one hour following the meal and between 60 and 130 mg/dl at three hours following the meal.[2]

The upper limit of fasting blood sugar levels is 125 mg/dl. An acceptable measurement is less than 110 mg/dl.[3] A person with a fasting blood sugar above the expected normal but not outside the diagnostic upper level, that is, somewhere between 110 and 125 (WHO standard) or 100 and 125 (American Diabetes Association standard) is said to have an “impaired fasting glucose,” (IFG), or prediabetes. If the measurement is 126 mg/dl or above, it is considered diagnostic for diabetes. Both prediabetes and diabetes require a repeat test to confirm the initial results.

Oral glucose test

Another test can be used to diagnose diabetes as well called the Oral Glucose Tolerance Test (OGTT).[4] While this test is an alternative to diagnosing diabetes, it is less often used in most patients due to the inconvenience of testing. It has been standardized by the World Health Organization (WHO). The test involves drinking 75 gm (the standardized amount) of anhydrous glucose after it has been dissolved in water. After the drink has been swallowed, the lab measures the venous blood sugar at 60, 90 and 120 minute intervals.

At the 2-hour or 120 minute interval, the OGTT level should not be outside that recorded for the random range. If the individual records a result that is higher than 140 but lower than 199 mgs/dl it is said they possess “impaired glucose tolerance” (IGT). People in this group are at a higher risk for heart and blood vessel disease. It can be as much as two times the level of the general populace. This state of IGT is also indicative of the potential of type 2 diabetes (T2D). The likelihood of developing type 2 diabetes is 5% within the first year. If the individual is of Hispano-American lineage the likelihood rises to 10%.[5]


If you have diabetes, you will require glucose testing to determine the level of blood sugar. This may be done at home or in the doctor’s office. At home, you may use a glucose meter. If you are at the lab or doctor’s the procedure is refined. If either method produces questionable results, you may have to take an OGTT. This will help clarify your blood glucose levels.  


[1] Guthrie, DW; and Guthrie, RA (2003). The Diabetes Source Book. New York: McGraw Hill.

[2] Stanley, K (2009). 50 Things You Need To Know About Diabetes. Alexandria, VA: ADA.

[3] Meltzer, SJ; and Belton, AB (2009). Diabetes in Adults. Toronto: Key Porter Books.

[4] American Diabetes Association (2009). Type 2 Diabetes. Your Healthy Living Guide. Alexandria, VA: ADA.

[5] Ibid

This article was originally published July 12, 2012 and last revision and update of it was 9/10/2015.