Insulin blood tests are essential tests done to diagnose and monitor diabetes. Diabetes is a very common lifestyle and genetic disorder that occurs in people around the world. In India, it is estimated that approximately 77 million people have been diagnosed with diabetes.

Diabetes is a lifestyle disorder. It requires a lot of modification in your diet as well as your lifestyle so that it can be efficiently controlled and managed. It can be difficult to live with diabetes. Hence, it is extremely important to get a diagnosis at the right time. If you observe any symptoms of diabetes in yourself or your close ones, consult your doctor and get all the necessary tests done so that the condition can be managed and controlled at the initial stage itself.

With so many cases of diabetes coming up each day. It is important that you stay updated about all the tests that are being done for the diagnosis of diabetes. In this article, we will discuss in detail about the insulin tests, who should get it done, when is it done, the pre and postprandial insulin test, how the test is done, its normal ranges, and the causes of low and high insulin levels in your blood.

What is an insulin test?

An insulin test is a blood test that measures the levels of insulin hormone present in your blood. The insulin hormone is responsible for moving glucose from your bloodstream into the cells. This provides your body with the energy that it needs to perform daily activities. Thus, insulin is an essential hormone required to regulate the levels of glucose in your blood. Abnormal insulin levels can indicate a serious health condition.

  • Hyperglycemia: Too high blood glucose levels caused due to insufficient levels of insulin in your blood.
  • Hypoglycemia: Indicates too low blood glucose levels. This happens because of increased levels of insulin that deliver too much glucose into your blood.

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What is a pre and post-prandial insulin test?

The pre-prandial insulin test also known as the fasting plasma glucose test (FPG) measures the level of glucose present in your blood after you have fasted for approximately 8 hours. It is best and most convenient to get this test done early in the morning when you have an empty stomach. Make sure that you do not eat or drink anything before your sample is collected for preprandial testing except water.

The postprandial blood sugar (PPBS) test means the level of glucose present in your blood approximately 2 hours after having a meal. The 2-hour gap between sample collection and food intake is kept because the blood sugar levels are at their peak 2 hours after you have had your meal. Therefore, it is a very important test to know how well your body is processing the sugar and starch that you consume during your meal. It helps your doctor in deciding your future treatment plan and dosage of medicines as well.

Who is the Pre and Postprandial Insulin test recommended for?

The pre and post-prandial insulin test is generally recommended for people who are at a higher risk of developing diabetes. The most common group of people who must get a pre and post-prandial blood test done are:

  • Females who are pregnant and have type I and type II diabetes or have a family history of high blood sugar
  • Females who have gestational diabetes, that is, diabetes tha develops during the pregnancy
  • People who are taking a new type of insulin or a different dosage than their usual medicine
  • People who have difficulty controlling their diabetes
  • People who are taking multiple medicines for diabetes as they have increased risk of reduced sugar levels
  • People with a history of blood sugar that rises after eating
  • People who are insulin resistant

When is a Blood Insulin test required?

A blood insulin test is required to understand how well your body responds to starch and sugar before and after a meal. Your doctor can recommend you an insulin test if you experience any of the symptoms given below:

  • Increased hunger
  • Sweating
  • Dizziness
  • Blurred vision
  • Fainting
  • Palpitations

Your doctor can even recommend you an insulin test if you are diagnosed with any of the following health conditions:

  • Poly Cystic Ovarian Syndrome (PCOS)
  • Type I and type II Diabetes
  • Metabolic Syndrome
  • Heart disease
  • Cushing’s disease
  • Insulinoma 

How are pre and post-prandial tests done?

Since an insulin test is a blood test, of course, your blood sample is collected for the pre and postprandial insulin test. Only the time at which the sample is collected differs in both tests. All other parameters are kept constant for accurate results. 

  • Fasting/ Preprandial insulin test: For the pre-prandial insulin tests, you are required to fast for a minimum of 8 hours before your blood sample can be collected for testing. After 8 hours of fasting, a small amount of your blood is taken to estimate the level of insulin present in your blood.
  • Insulin postprandial test: For the postprandial test, the blood sample is collected 2 hours after you have had your meal. This test is used to detect diabetes and is commonly known as plasma glucose concentrations after eating.

What are the normal ranges of pre and postprandial insulin tests?

The normal range of pre and postprandial insulin tests can vary from one laboratory to another. The normal value of a blood sugar test depends on whether you have diabetes, prediabetic, or non-diabetic. The average normal blood sugar levels in all three situations are summarised in the chart below:

S.No. Group Fasting Blood Sugar Level (mg/dL) Postprandial (PP) Blood Sugar Level (mg/dL) (2 hrs after eating)
1. Normal  70 – 100 < 140
2.  Early diabetes 101 – 126 140 – 200
3. Diabetes > 126 > 200

Normal Post prandial blood sugar level in Healthy people

According to the ADA, the normal blood glucose levels in a non-diabetic healthy individual in mg/dL during different times of testing are given in the post-prandial blood sugar chart below:

S.No. Condition Blood Glucose Level (mg/dL)
1. 1 hour after meals 90 – 130
2. 2 hours after meals 90 – 110
3. > 5 hours after eating 70 – 90

Normal Post prandial blood sugar level in Diabetic people 

The blood sugar level in diabetic individuals depends largely on their age. The blood sugar levels according to the age of the people with diabetes at different times of testing is summarised below:

S.No. Age Normal blood sugar level (mg/dL) (1-2 hours after eating)
1. < 6 years ~ 180
2. 6 – 12 years Up to 140
3. 13 – 19 years Up to 140
4. > 20 years < 180

Normal postprandial blood sugar range in Females

The normal blood sugar levels are different for pregnant and non-pregnant women of the same age. The normal blood sugar levels for pregnant diabetic women are:

S.No. Condition Normal Blood Glucose Level (mg/dL)
1. Fasting 70 – 89
2. Before meals 89
3. 1-2 hours after meals < 120
4. Bedtime  100 – 140

Postprandial blood sugar chart in Pre-Diabetic people

According to the ADA and Diabetes UK, the normal blood sugar levels in prediabetic people are given in the chart below:

S.No. Condition Normal Blood Glucose Level (mg/dL)
1. Fasting 100 – 125
2.  2 hours after meal 140 – 199

What are the causes of low insulin levels?

The insulin levels in your blood can be due to various reasons. The major causes of low insulin levels in the blood are

  • Type I diabetes: It is an autoimmune condition wherein the pancreatic cells responsible for producing insulin are destroyed.
  • Pancreatic disease: There are various other diseases apart from type I diabetes like pancreatitis that can interfere with the functioning of the pancreas or damage the pancreatic cells. 
  • Removal of the pancreas: Pancreatectomy, that is, the surgical removal of the pancreas is another cause of low insulin levels in your blood.
  • Hypopituitarism: It is also known as pituitary insufficiency which is a rare condition wherein the pituitary gland does not make enough hormones.

What are the causes of high insulin levels?

Just like low insulin levels, the insulin levels can increase in your bloodstream due to some underlying cause. The major causes of high insulin levels are

  • Insulin resistance: It is the condition wherein your body cells become resistant to the effects of insulin. Due to the resistance, the pancreas releases extra insulin to compensate which eventually raises the levels of insulin in your blood.
  • Obesity: Increased weight and insulin levels are connected to each other. As you become obese, the cell’s response to insulin is impaired leading to insulin resistance and higher levels of insulin. Similarly, an increase in insulin levels can also lead to increased weight.
  • Type II diabetes: It is the most common cause of increased insulin levels. 
  • Insulinomas: Insulinomas are a condition wherein benign tumours are present in the pancreas that produce insulin. The symptoms of untreated insulinomas include increased hunger, visual disturbances, anxiety, dizziness, weakness, heart palpitations, and even coma in severe cases.
  • Pancreatic cell hyperplasia: It is a condition wherein more cells in the pancreas are made. These cells are generally normal and not tumorous. However, they increase the production of insulin in your body.
  • Cushing’s syndrome: It is a rare disease that increases the levels of insulin in your blood. The rare disease is characterised by excess production of cortisol in your body, loss of muscle mass, and the reduced ability of your muscles to take up insulin from the blood. The main cause of this syndrome is usually a pituitary tumour.
  • Acromegaly: It is a rare disease that increases the production of growth hormone and insulin-like growth factor-1. An increase in the levels of growth hormones causes increased production of insulin as well.
  • Medicines: There are certain medicines that increase the levels of insulin in your body. These medicines include corticosteroids (used for reducing inflammation), sulfonylureas (used for the treatment of type II diabetes), and oral contraceptives. 
  • Pregnancy: It is common for insulin levels to increase during pregnancy.

What inferences can be drawn from an insulin blood test?

Depending on the levels of insulin present in your blood during the preprandial insulin test and the fasting glucose test results, your doctor can get an idea about the main cause leading to the abnormal levels of insulin in your blood. It is very important to estimate these inferences so that effective treatment can be planned. The table below lists the most possible inferences that can be drawn from an insulin blood test:

S.No. Pre-prandial (fasting) insulin level Fasting glucose level Inference  Disorder 
1. Normal  Normal  Normal blood parameters No associated disorder
2. High  Normal or slightly increased Insulin resistance
3. Low  High  Beta cells are not producing enough insulin Diabetes, pancreatitis
3. Normal or high low Excess insulin production causing hypoglycemia Cushing’s syndrome, Insulinomas, increased administration of exogenous insulin.


The insulin blood test is an important parameter to check how well your body is responding to the starch and sugar. It is equally important to get this test done at the right time so that the results are accurate and reliable. Now that you know the importance of pre and postprandial insulin tests, make sure you get the pre-prandial insulin test after 8 hours of fasting and the postprandial insulin test after 2 hours of your meal only. 

Frequently Asked Questions (FAQs)

  • Can a postprandial blood glucose test be done at home?

Yes, you can easily do a postprandial blood glucose test at home.

  • Can I drink water before fasting insulin test?

You can only have water for 8 hours before your sample is taken for a fasting insulin blood test. You should not eat or drink anything else apart from water.

  • How can I decrease insulin levels?

Insulin levels can be decreased through mild changes in lifestyle and diet. These include:

  • Have a healthy and balanced diet
  • Aim to lose weight if you are obese
  • Exercise regularly
  • Have proper and sound sleep
  • Limit alcohol consumption
  • Take vitamin and mineral supplements

Ms. Srujana is Managing Editor of Cogito137, one of India’s leading student-run science communication magazines. I have been working in scientific and medical writing and editing since 2018. I am also associated with the quality assurance team of scientific journal editing. I am majoring in Chemistry with a minor in Biology at IISER Kolkata.

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