Know Your Diabetes Test!

What do RBS, FBS, PPBS, HbA1c actually mean?


India has 65 million diabetics and 77 million pre-diabetics. That’s about 12% of the population of a young nation! Get tested and manage diabetes. Did you know that uncontrolled blood sugar can damage your nerves and blood vessels and ultimately affect your heart, kidney, eyes, etc.


If you are over 40 years, are overweight or have a family history of diabetes, you are at high risk of developing diabetes. So, it’s advisable to get tested every year. If you already have diabetes, it’s advisable to get regular tests every 3-6 months.


Diagnostic tests are available to screen a person for diabetes as well as to monitor those who already have diabetes. The purpose of these tests is to ensure early diagnosis as well as to monitor the efficacy of your diabetes therapy.


Tests for Diabetes

Common tests for Diabetes Screening & Disease Management include Random Blood Sugar (RBS), Fasting Blood Sugar (FBS), Post Prandial Blood Sugar  (PPBS), Glycated Haemoglobin (HbA1c) and Oral Glucose Tolerance Test (OGTT). In some cases, fasting and post-prandial urine examinations may also be required to check presence of glucose (or sugar) in the urine.


Sample Required

Blood (sometimes urine examination may also be needed) 


1) Random Blood Sugar (RBS)

Also referred to as “casual testing”, RBS does not require any fasting and, as such, can be done anytime at short notice. If your RBS levels are off the normal range, your doctor will prescribe a fasting blood sugar test to confirm if you have diabetes. RBS may also be prescribed to people who already have diabetes to monitor how the disease is being managed.


Normal Range:  70-125 milligrams per deciliter (mg/dl)

Pre-Diabetes: 140-200 mg dL

Diabetes: > 200 mg dL


Pre-diabetes is a condition where blood sugar levels are higher than normal, but not high enough to be classified as full-blown diabetes.


2) Fasting Blood Sugar (FBS)

This will probably be the first test prescribed by your doctor if he suspects you are at risk for developing diabetes. FBS is the most common test for diabetes screening. It requires fasting for 10-12 hours (only water intake is allowed; no tea or coffee; medicines for diseases other than diabetes can be had with water).


Normal Range: 70-140 mg/dl

Pre-Diabetes: 100-125 mg / dL

Diabetes: >126 mg /dL


If your fasting blood sugar levels are high enough to be classified as diabetes, it is possible your doctor may ask for a urine test to confirm the diagnosis.


3) Post-Prandial Blood Sugar (PPBS)

This is done two-hours after eating a meal. Normally, blood glucose levels increase after eating – this causes the pancreas to release insulin (which removes glucose from the blood and stores it for energy). After some time, the blood glucose levels start to dip and finally come down to normal range. However, it may remain elevated in people with diabetes. This is why PPBS is recommended for people with diabetes to determine how successful they are in controlling their blood sugar. In PPBS, blood is collected two hours after a meal (no food or drinks are permissible in the interim period). 


Target Range: 90-140 mg / dL


4) Glycosylated Haemoglobin (HbA1c)

This indicates your average blood sugar level for the past 2-3 months. It measures the percentage of blood sugar attached to haemoglobin, i.e., the oxygen-carrying protein in the red blood cells. The higher your blood sugar levels, the more hemoglobin you'll have with sugar attached. HbA1c gives an overall picture of what your average blood sugar levels have been over the last 2-3 months. This is important for people with diabetes as higher your HbA1c, greater the risk of developing diabetes-related complications. This is why HbA1c is often prescribed for people with diabetes at least once or twice a year.


Fasting is not essential for HbA1c. However, some doctors say it's preferable to fast for 10-12 hours before the test.


Normal Range: 4-5.7%

Pre-Diabetes: 5.8-6.4 %

Diabetes: ≥ 6.5 %


5) Glucose Tolerance Test (GTT)

In this test, 75 gm of glucose is given orally after taking the fasting blood and urine samples. Thereafter, blood and urine samples are drawn every half-an-hour for two hours to determine how quickly your body breaks down the glucose. Based on the results, a curve is drawn to determine the condition of the patient. GTT is commonly used during pregnancy to diagnose gestational diabetes. Gestational diabetes is a condition wherein a pregnant woman, who is not diabetic, has high blood sugar levels as a result of her pregnancy.


GTT requires overnight fasting for 10-12 hours. Normally, the blood glucose level should come down to about 140 mg/dl after two hours, so an elevated level gives an indication of being pre-Diabetic or Diabetic.


6) Urine Test

Normally, urine contains no glucose because the kidneys re-absorb all the filtered glucose back into blood stream. The normal threshold limit of kidneys is about 180 mg/dl of blood. If the blood sugar level is beyond the threshold level, due to any reason, the kidneys will try to excrete the extra amount of sugar in the urine.


- Dr. S. P. Datta, MBBS, General Physician


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