Blood Sugar (Glucose) Fasting (FBS), PP (Post Prandial) & Random

Clinical definition of the Blood Sugar (Glucose) test
Glucose is a type of sugar that serves as the main source of energy used by the body. Insulin is a hormone that helps the body's cells to use the glucose. Excess or shortage of insulin in the body causes an imbalance of the blood glucose in the body, leading to its severe drop or drastic increase in the blood. Blood glucose levels that remain high over time can cause damage to the eyes, kidneys, nerves and blood vessels. Chronic low glucose levels can lead to brain and nerve damage.
There are several different kinds of glucose tests:

  • Fasting blood sugar (FBS): Measures blood sugar levels either after an 8-12 hrs or overnight fast
  • 2-hour postprandial blood sugar (PP or PG): Measures blood sugar exactly 2 hours after eating a meal or a specific amount of glucose (Post Glucose blood sugar)
  • Random blood sugar (RBS): Measures blood sugar regardless of when the last meal was. Random testing is useful because glucose levels in healthy people do not vary widely throughout the day
  • Glucose tolerance test (GTT): Measures the blood glucose levels at specified timed intervals (usually 30mins) after the intake of a standard quantity of liquid glucose

Why is the Blood Sugar (Glucose) test done?
The glucose test is a type of blood test used to determine the amount of glucose in the blood. It may used for the following purposes:

  • As a screening procedure during routine health checkups to determine if the blood glucose level is within healthy ranges
  • To screen, diagnose, and to monitor the treatment of
    • Hyperglycemia
    • Hypoglycemia
    • Diabetes
    • Pre-diabetes
  • To check for diabetes that occurs during pregnancy (gestational diabetes)
  • To monitor glucose levels in persons with diabetes
  • Urine glucose analysis is usually done as part of a routine urinalysis

What are the common signs/symptoms when the Blood Sugar (Glucose) test is done?
The symptoms associated with hyperglycemia (abnormally high blood sugar) are as follows:-

  • Increased thirst
  • Increased urination (especially at night)
  • Unexplained increase in appetite
  • Unexplained weight gain or weight loss
  • Fatigue
  • Giddiness
  • Extreme tiredness
  • Blurred vision
  • Slow-healing infections
  • Erection problems
  • Irregular menstrual cycles
  • Tingling sensation or numbness in the hands and feet

Symptoms associated with hypoglycemia (abnormally low blood sugar) are as follows:-

  • Sweating
  • Hunger
  • Trembling
  • Anxiety
  • Confusion
  • Blurred Vision

Who should do the Blood Sugar (Glucose) test (Target population)?
Persons showing the above signs & symptoms. It may also be done by:-

  • Healthy individuals during routine health checkups
  • As a pre-operative work up
  • Pregnant women
  • Diabetics who are on and off their regular medications
  • People on lipid lowering medications

What should I do before the Blood Sugar (Glucose) test?

Specimen type

Specimen collection procedure

Preparatory instructions during specimen collection*

Serum / Plasma (Blood Sample)

Venipuncture - (Collection of blood from a vein, usually from the arm)

Fasting Required.

Fasting samples have to be collected after a minimum 8-hour overnight fasting status.

Clear fluids like water is allowed during this period. Refrain from consumption of early morning beverages like tea, coffee and milk until specimen collection is completed.

In case of diabetics on oral or injectable hypoglycemic agents, consult your physician about continuing with these medications prior to specimen collection.

For a 2-hour postprandial test, the meal must be eaten exactly 2 hours before the blood sample is taken.

No special preparation is required before having a random blood sugar test.

*Subjects suffering from any illness or on oral or injectable medications are advised to consult their physician prior to requesting any tests or procedures.

How do I interpret my Blood Sugar (Glucose) test results?

Blood Sugar (GOD-POD method)




Normal Glucose Tolerance




Impaired Glucose



Provisional Diag. Diabetes Mellitus


> 200

Urine Sugar




Inference: A Glycocylated Hb (HbA1C) & urinary microalbumin test is recommended at regular intervals in diabetic patients.

‘*A Reference range is a set of values which helps the healthcare professional to interpret a medical test. It may vary with age, gender, and other factors. Reference ranges may also vary between labs, in value & units depending on instruments used and method of establishment of reference ranges’

Diseases/conditions related to the Blood Sugar (Glucose) test

  • Diabetes Mellitus Type 1
  • Diabetes Mellitus Type 2
  • Gestational diabetes
  • Pre diabetes (also called as Impaired fasting glucose)
  • Diabetic ketoacidosis
  • Nonketotic hyperosmolar coma
  • Chronic renal failure
  • Diabetic retinopathy
  • Chronic pancreatitis
  • PCOS
  • Glucagonoma
  • Hyperthyroidism
  • Pancreatic cancer
  • Pancreatitis
  • Hypopituitarism
  • Hypothyroidism

Other tests related to the Blood Sugar (Glucose) test

  • Fasting blood sugar (FBS)
  • 2-hour postprandial blood sugar (PP or PG or PPBS)
  • Random blood sugar (RBS) 
  • Glucose tolerance test (GTT)
  • Oral glucose tolerance test (OGTT)
  • HBA1C
  • Microalbumin 
  • Insulin
  • Insulin C-peptide
  • Insulin antibody
  • IGF-1
  • IGF-BP-3
  • Glucagon
  • Urinalysis

Synonyms : Urine sugar
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Blood Sugar(Glucose) FBS(Fasting) and PP(Post Prandial)