Diet and Nutrition

How Is Diabetes Diagnosed?

How Is Diabetes Diagnosed?

Are you wondering if you have diabetes? Do you fall in the high-risk category for diabetes? Are you experiencing any of the symptoms of diabetes such as increased thirst, frequent urination, and feeling hungry more than usual? Do you want to confirm if you have diabetes? Checking your blood sugar level is the only way to know for sure if you have developed diabetes.

The following tests are performed to confirm if you have diabetes:

  1. Fasting blood sugar test (FBS)
  2. Random blood sugar test (RBS)
  3. Glycosylated hemoglobin test (HbA1c)
  4. Oral glucose tolerance test (OGTT)

What is a fasting blood sugar (FBS) test?

An FBS test is a blood test wherein your blood is drawn after an 8-hour fasting and checks your blood sugar level. A fasting blood sugar level of above 126 mg/dl confirms diabetes.

What is a random blood sugar (RBS) test?

When your doctor requests for an RBS, your blood is drawn at any time of the day to check your blood sugar level. This test does not follow any criteria such as fasting or taking specific amounts of glucose like in the case of an oral glucose tolerance test. As the test's name implies, an RBS test mainly uses a random blood sample to measure the level of glucose in the blood.

An RBS result of more than 200 mg/dl confirms diabetes.

What is an HbA1c test?

The hemoglobin A1c or glycosylated hemoglobin test measures an individual's average blood sugar level over a period of 2-3 months. In this type of glucose test, there is no fasting required. A person's blood can be randomly drawn at any time of the day. HbA1c above 6.5 mg/dl confirms diabetes.

In some patients who have diabetes, having an elevated level of HbA1c after a period of 90 days signifies poor diabetes control. People with diabetes are at high risk of developing cardiac problems. To address such risks, doctors highly recommend lowering one’s LDL (low-density lipoprotein or bad cholesterol), maintaining a balanced diet, engaging in regular exercises, and controlling one’s blood pressure.

Oral Glucose Tolerance Test (OGTT)           

A glucose tolerance test is a test wherein you will be given a glucose solution to drink before collecting a sample of your blood for testing. This test is usually done after an overnight fasting or fasting for a period of at least 8 hours.

  • In the beginning, your blood is drawn to check your fasting blood sugar level.
  • After this, you will be asked to drink a glucose solution that contains 75 grams of glucose.
  • After 2 hours of drinking this solution, your blood is drawn again to check your blood sugar level.
  • A 2-hour OGTT value of above 200 mg/dl confirms diabetes.

In short, any one of the following values confirms diabetes:

  1. A fasting blood sugar level of more than 126 mg/dl
  2. An HbA1c result of more than 6.5 mg/dl
  3. A 2-hour OGTT test value of more than 200 mg/dl
  4. A random blood sugar (RBS) of more than 200 mg/dl

Your doctor may want to repeat your blood tests after some time to monitor your condition.

Diagnosing Gestational Diabetes

Diabetes that occurs only during pregnancy is called as gestational diabetes. This type of diabetes usually disappears after the childbirth. The placental or umbilical cord hormones are usually responsible for this condition among pregnant women. A pregnant woman who falls in the low-risk category for gestational diabetes is usually screened during the 24th to 28th week of her pregnancy.

If you fall in all of the following criteria, you may not be at risk of developing gestational diabetes:

  • Age: If you are less than 25 years old.
  • Weight: If you have a normal weight with a body mass index (BMI) of 18.5 to 24.9. BMI values are based on your height and weight.
  • No family history of diabetes: If your parents, siblings, or relatives don't have a history of diabetes.
  • Not a member of high-risk racial groups: Includes Hispanic American, African American, Pacific Islander, Native American, or Asian American.
  • No history of gestational diabetes from previous pregnancies
  • Not suffering from a high blood pressure

If you fall into the high-risk category, your doctor may want to perform an OGTT in your first prenatal checkup (your first appointment with your doctor wherein you confirm your pregnancy). Gestational diabetes occurs in 9.2 percent of pregnancies.

OGTT for the Diagnosis of Gestational Diabetes

To confirm the diagnosis of gestational diabetes among pregnant women, an OGTT is performed. First, you are given a glucose solution that contains 50 grams of glucose. Your blood is then drawn after an hour to check your blood sugar level. If the result is below 140 mg/dl, it is normal. Having a normal OGTT result means that you do not have gestational diabetes. However, if your OGTT values exceed 140 mg/dl, you will be asked to undergo another glucose test.

For the Repeat Test

If your blood glucose from the initial test is relatively high, you will be advised by your doctor to undergo another glucose tolerance test. This time, it is the 3-hour glucose tolerance test. For this test:

  • You are not allowed to consume anything (food and drinks) for a period of 8-14 hours before the test. You cannot also eat during the glucose test.
  • You will be given a glucose solution of 100 grams to drink.
  • Your blood will be collected before drinking the glucose solution and every hour for three consecutive times. Your blood glucose level will be checked for each time.
  • This test lasts for at least three hours.

The table below shows the times of fasting with their corresponding normal values.


Normal Values


Below 95 mg/dl

At the end of 1 hour

Below 180mg/dl

At the end of 2 hours

Below 155 mg/dl

At the end of 3 hours

Below 140 mg/dl

This is how your test is interpreted:

  • If all the above values fall in the normal range, it means that you don’t have gestational diabetes.
  • If any one of the above values is higher, your doctor may ask you to modify your diet.
  • If any two of the above values are higher, your doctor will confirm that you have gestational diabetes.

An early diagnosis and a timely follow-up of your treatment plan will prevent or delay the development of diabetes complications.