Know Your Fasting, Random and Postprandial Blood Sugar Level

Postprandial blood sugar level Posted On


Do you know how much normal blood sugar is in our body? Today, we will discuss fasting, random and postprandial blood sugar levels. 

Blood sugar plays an essential role in our body. It gives you the constant energy that requires in your daily life. 

If your blood glucose rises and crashes, you could be at risk of diabetes. On the contrary, low blood glucose is also wrong because it can cause hypoglycemia. 

Your blood glucose constantly fluctuates the entire day. There are specific normal ranges of your blood glucose. It would be best to keep your blood glucose in normal ranges for a healthy and disease-free life. 

In this post, we will discuss all important blood sugar parameters – 

  • Fasting blood sugar level (FBS)

  • Random blood sugar level (RBS)

  • Postprandial blood sugar level (PPBS)

  • HbA1C 

Let’s get started. 


What do you mean by blood sugar?

Blood sugar means the glucose present in your blood. Whatever you eat in your daily life eventually converts into glucose. This glucose is a primary fuel of our body that gives us energy in the form of ATP


Why do we need normal blood sugar levels in our bodies? 

We know that glucose is an essential compound for energy. Most organs do not require a continuous supply of glucose for energy. So, we can survive even in fasting conditions for a few days. 

But three organs need the highest energy demand and continuous supply of glucose. These organs are – 

1. Central Nervous System (CNS)

Glucose is a preferred fuel for your brain and nervous system because it needs constant delivery of glucose. 

The main reason is that glucose can easily cross blood-brain-barrier (BBB). 

Your CNS cannot use fatty acids for energy because free fatty acids usually bind with albumin, and this albumin does not cross BBB. 


2. Eye 

The retina is a vital eye part that totally depends on glucose. This is your second organ that needs a continuous delivery of glucose. 


3. Reproductive organs 

Testes and ovaries are gonads that produce sperm or ova to pass DNA. 

In these gonads, special cells (i.e., germinal epithelium) are present. This germinal epithelium also depends on glucose for energy. 


What test checks blood sugar levels? 

There are specific diagnostic tests to determine glucose content in your blood. It could be normal, high, or low blood sugar level, depending upon your lifestyle. 

Your blood sugar level can be checked by these blood sugar tests – 

  • FBS test 

  • PPBS test

  • RBS test

  • HbA1C Test

Postprandial blood sugar level


What is the FBS test? What are normal and high levels of FBS?

The FBS full form is the Fasting Blood Sugar test. This test is done in a fasting condition.

The FBS test means you must do an overnight fast for over 8 hours. After that, a blood sample will be taken and determine your blood glucose level. It is also known as the “Pre-prandial blood sugar” or “Fasting Blood Glucose” test. 

Many trusted government authorities like the CDC and WHO suggest that the normal range of FBS should not be more than 100 mg/dl. 

If your blood glucose is over 100 mg/dl and below 125 mg/dl, it indicates a prediabetic condition or early diabetes. 

You will be considered a person with diabetes if your fasting blood sugar exceeds 126 mg/dl. 

In this condition, you need to monitor your other blood sugar parameters. Your doctor may correlate your symptoms with blood glucose results. 

Postprandial blood sugar level


What is the PPBS test? What are normal and high levels of PPBS?

The PPBS test full form is Postprandial Blood Sugar. It means “blood sugar level after meal”. You have to take a meal, and after 2 hours, you need to check your blood sugar level. 

In the UK, US or other countries, giving 50 g of Glucose dissolved in 250 to 300 ml of water is more accurate. Then blood sugar level is checked after 2 hours. It is called “Glucose Tolerance Test (GTT)”. 

Your PPBS normal value should not be more than 140 mg/dl. 

If your PPBS range falls between 140 to 199 mg dl, it indicates a prediabetic condition. 

You will be considered a person with diabetes if your PPBS range is more than 200 mg/dl. 

Postprandial blood sugar level


Why is your postprandial blood sugar important?

Postprandial blood sugar is the best and most accurate way to assess your blood sugar level.  

When you take a meal, your blood sugar level starts rising just after 10 mins, and it is at peak level after two hours.

Your body tries to manage blood glucose after a meal. During the postprandial phase, your pancreas releases insulin to regulate high blood sugar levels.

Unlike fasting blood sugar, PPBS gives you a clear picture of what your body does and how your body responds when you eat.

If your blood glucose level remains elevated for a long time, even after many hours of food, it indicates “Insulin resistance”.

Your pancreas continuously releases insulin whenever you eat high-carbohydrate food and snacks. This increased insulin may cause desensitisation or downregulation of the insulin receptor (Tyrosine Kinase).

This Insulin resistance is a major risk factor for Type 2 diabetes mellitus.

PPBS is an important tool for diagnosing prediabetic or type 2 diabetes mellitus. This test also helps to monitor the effectiveness of current diabetic treatment.


What is RBS test? What are normal and high levels of RBS?

The RBS full form is a Random Blood Sugar test. This measures your blood sugar at any random time of the day. You can perform this test without fasting or after eating food. 

There is no specific range for normal or prediabetic. This RBS test is usually done to diagnose diabetes. 

Suppose you have taken food, and within just 15 mins, you get a blood sugar level of 190 mg/dl. It would be believed a normal blood sugar level. 

But if your random blood sugar level is more than 200 mg/dl, it indicates a diabetic condition.  

Postprandial blood sugar level


What does the HbA1c test indicate?

The HbA1c full form is haemoglobin A1C or glycated haemoglobin test. 

When glucose enters your blood circulation, it gets attached to the haemoglobin of your red blood cells.  

Almost everyone has some sugar attached to their haemoglobin. Still, diabetic patients will have a high amount of glucose attached to haemoglobin. 

Using HbA1c tests, you can determine your average blood sugar levels over the past three months.

It is considered a gold standard biomarker to diagnose prediabetes or diabetes. 

If you have a high HbA1C (>6.5%), it means you have too much sugar in your blood, which indicates diabetes. 

According to CDC, the expected average blood glucose level of HbA1C is mentioned in the below table – 

 HbA1c test


A1C %

Estimated average blood glucose



<117 mg/dl


5.7 to 6.4%

117 to 130 mg/dl



>140 mg/dl



154 mg/dl


183 mg/dl


212 mg/dl


240 mg/dl


Postprandial blood sugar level


What level of blood sugar is dangerous?

Suppose your blood sugar level is more than normal blood sugar; it becomes toxic in your body. 

You will be considered a diabetic person if you find the following elevated blood sugar parameters in your report – 

  • Fasting blood sugar level (FBS) is more than 100 mg/dl 

  • Postprandial blood sugar level (PPBS) is more than 140 mg/dl 

  • Random blood sugar level (RBS) is more than 200 mg/dl

  • HbA1C is more than 6.5%


Conversely, a very low blood sugar level is also bad for you. Suppose you find a blood sugar level of less than 60 mg/dl; it indicates hypoglycaemia.  

Hypoglycaemia is a dangerous condition where you get abnormal CNS-related problems. Because the central nervous system is your primary part, it needs a continuous supply of glucose. 

If your brain does not get enough glucose during low blood sugar conditions. In that case, you will feel irritation, abnormal behaviour, tremor, unconsciousness, seizure etc. 

Therefore, your blood sugar level should be neither high nor low. 



We have learned how normal blood sugar regulates all body functions. If it gets imbalanced, you may have several health problems. 

There are 3 crucial blood test parameters (FBS, PPBS and RBS) that give you instant results.  

The fasting blood sugar (FBS) is more specific after 8 hours of fasting. While postprandial blood sugar (PPBS) is more accurate if you do a PPBS test after 2 hours of eating. 

The rest of the time would be considered random blood sugar (RBS). 

You should keep your blood sugar level within normal range, like FBS < 100 mg/dl, PPBS < 140 mg/dl and RBS <200 mg/dl. 

You should consult your doctor if your blood sugar does not fall in these ranges. 

This was information about blood sugar.

Please share this post if you found this article informative. 



Q 1. Is 200 blood sugar normal after eating?

No. If your blood sugar is more than 200 mg/dl after a meal or without eating a meal, it would be considered an abnormal blood sugar level. It indicates prediabetic or type 2 diabetes mellitus. 


Q 2. What should blood glucose level be after a meal?

Your blood sugar level should be less than 140 mg/dl after 2 hours of eating. This is called Postprandial blood sugar level. If your blood sugar level usually remains less than 200 mg/dl throughout the day. This is called a Normal Random Blood Sugar level.  


Q 3. Can postprandial blood sugar levels be less than fasting blood sugar levels?

The normal range of postprandial blood sugar is 100 to 140 mg/dl. If you find blood sugar is less than 100 mg/dl even after having food. It means your body is releasing more insulin. This can drop your blood sugar, which may lead to hypoglycaemia. 


Q 4. How is a postprandial blood sugar test done?

Postprandial blood sugar is usually performed after two hours of eating food. 


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