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A blood sugar test is a test to measure the amount of sugar, or specifically glucose, in your blood. Glucose is a major source of energy for cells of the body, including brain cells. The human body breaks down most carbohydrates from the foods we eat and converts them to a type of sugar called glucose. This can raise your blood sugar level if the glucose control mechanisms of the body fail.

Blood sugar level refers to the amount of sugar that gets absorbed into the bloodstream after consuming food. It peaks an hour after eating and eventually drops. Blood sugar levels are kept in check by the hormone Insulin secreted from the Pancreas. If the pancreas produces little or no insulin (as in Type 1 Diabetes Mellitus) or if the insulin produced is insufficient to meet the needs of the body and/or despite being sufficiently produced, it is not properly utilized by the body aka insulin resistance (as in Type 2 Diabetes Mellitus), then the blood sugar levels rise.

As part of a routine check-up, your doctor may order a blood sugar test which will measure the amount of glucose in your blood. They may also be checking to see if you have diabetes or prediabetes, a condition where your blood sugar levels are higher than normal yet lower than for Diabetes. 

Different tests are done to assess Blood Glucose Levels and the latest criteria for diagnosis of diabetes as per The American Diabetes Association (January 2022)

FBS (Fasting Blood Sugar)

FBS is blood glucose measurement after fasting for 8 -10 hours (minimum of 8 hours).  It is recommended to do FBS in the morning on an empty stomach. It is best to not eat or drink any fluids except water for 8-10 hours before the test. 

Result HbA1c
Normal less than 5.7%
Prediabetes 5.7% to 6.4%
Diabetes 6.5% or higher

RBS (Random Blood Sugar)

RBS is a blood glucose measurement taken at any time of the day without considering whether the person was fasting or not and any reading equal to or above 200 mg/dl indicates Diabetes Mellitus.

PPBS (Post Prandial Blood Sugar or After food Blood Sugar)

The post prandial blood sugar test measures the glucose in the blood two hours after eating a meal. It helps the clinician understand whether a patient is diabetic or the treatment is ineffective. Ideally, the reading should not go beyond 200 mg/dl. 

HbA1c (Glycated/Glycosylated Hemoglobin level)

This indicates the level of glucose in the blood that is chemically bound to hemoglobin. Normally, HbA1c is a measure of the average blood glucose for the previous 3 months. This can give you an understanding of whether your glucose levels were under control or not or if you are prone to Diabetes. One need not fast for this test.

Result HbA1c
Normal less than 5.7%
Prediabetes 5.7% to 6.4%
Diabetes 6.5% or higher

Note: Tests mentioned above (FBS, RBS, PPBS, HbA1c) are more useful to “assess the likelihood of diabetes and to assess the progress of treatment”.

GTT (Glucose Tolerance Test)

This test measures your body's response to sugar (glucose). The GTT can be used to screen for type 2 diabetes and hence often done to diagnose diabetes.  Even before one’s fasting blood glucose level becomes abnormal, doing a GTT helps to identify abnormalities in the way the body handles glucose after a meal. The commonly employed glucose tolerance test is the oral glucose tolerance test (OGTT). A blood sample will be collected prior to the test. You will then be asked to drink a syrupy glucose solution usually containing 75 grams of glucose. Your blood will be taken again two hours after you drink the solution. 

Result Oral Glucose Tolerance Test (OGTT)
Normal less than 140 mg/dl
Prediabetes 140 to 199 mg/dl
Diabetes 200 mg/dl or higher

How is a Blood Sugar Test Performed?

To get a blood sample, your healthcare provider will insert a needle into your vein and draw blood. Your doctor will ask you to fast for 8-10 hours before the FBS test. You do not need to fast before the A1C test.

What do the results of the Blood Sugar Test indicate?

Based on your condition and the timing of your test, your blood sugar levels should be in the ranges listed below:

  Pre-diabetes Diabetes Mellitus
FBS 100 – 125 mg/dL 126 mg/dL or more
GTT 140 -199 mg/dL 200 mg/dL or more
HbA1c 5.7 – 6.4% 6.5% or more

What readings would indicate Diabetes?

  • Two fasting blood sugar tests were taken consecutively, providing a result higher than 125 mg/dl.
  • A random blood sugar test shows glucose levels higher than 200 mg/dl.
  • A GTT indicated levels higher than 200 mg/dl at two hours.
  • An A1c test that reads equal to or more than 6.5%.

Take-Home Message/Importance of doing Blood Sugar Tests

“Prevention is better than cure” – It is advised to monitor sugar levels at timely intervals so as to weigh one’s probability to develop the disease and also to catch the disease at the root so that reversal of disease progression may be done by early detection. Your health is important to you and all of us at Aster Labs – make sure to find an Aster Labs near you and start your screening for Blood Sugar right away!