The Importance of Blood Tests To Detect Diabetes
Written by Dr. César Giral

Many people become aware that they have diabetes through blood tests done for other purposes or by way of a general medical examination. In other cases, laboratory tests are performed by medical order based on the patient’s symptoms and/or the presence of risk factors. The results of these exams tend to be fast and interpretation of the data is made within the context of a profile obtained through physical examination and the clinical history of each individual.

These are the most common tests and their practical use:

1. Fasting Blood Glucose

Fasting blood glucose or base is a value obtained by processing a blood sample taken in the morning, after resting during the night and without solid food or liquid (other than water) for at least the previous  eight 8 hours.

We must remember that the amount of glucose in our blood naturally fluctuates within a certain value range that is considered “normal.” The more elevated values or numbers are observed by eating breakfast  and the lower values on an empty stomach. Normally, after food intake, if the regulatory mechanisms of our bodies function adequately, the value of glucose in our blood should not exceed 200mg/dl (milligrams per deciliter). If is is not done on an empty stomach, the glycemic value should not exceed 100mg/dl to be considered normal.

What does an altered fasting blood glucose signify?

a)     A fasting blood glucose test of less than 70mg/dL is considered hypoglycemia.

b)     A number between 70 and 100mg/dL is considered normal.

c)     A fasting blood glucose test of between 100 and 125mg/dL is considered high and is therefore an indication of pre-diabetes. In this case, it is best to repeat the test for the second time or to perform a glucose tolerance test to evaluate more exactly the metabolic capacity to manage glucose. This will confirm pre-diabetes and allow certain therapeutic measures to be taken. At this point, medical criteria and good communication between doctor and patient is very important to successfully manage the situation.

d)     A fasting blood glucose test having a value of more than 125 mg/dL should be considered  very suggestive  of diabetes. If a second test shows such results, the diagnosis is confirmed. In those cases where the first number obtained is superior to 200mg/dL and symptoms (hunger, frequent thirst, increased frequency of urination. weight loss) exist, a second test is usually not necessary.

It is important to clarify that in persons with diabetes, the levels of fasting blood glucose a little above those considered normal, can be deemed acceptable, up to 140mg/dl (without breakfast).

2. Oral Glucose Tolerance Test

This test is used less frequently because it costs more and is more complicated to effect. It is done by measuring the levels of fasting blood glucose one or two hours after ingesting a sweetened liquid containing 75 grams of sugar. Because the symptoms of type 1 diabetes are very clear, this test is generally applied for the detection of type 2 or gestational diabetes. These two tests for blood glucose are important for the diagnosis of pre-diabetes and type 2 diabetes – as long as the interpretation is done  within the global context of data obtained in the clinical history and physical exam of the person in question.

In other articles, we will share additional tools for the control and continued observation of diabetes, including capillary glucose and glycosylated hemoglobin test (hemoglobin A1c).


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Dr. César Giral

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