Blood Glucose Test: Preparation, Procedure and Principle


A Blood Glucose Test measures blood glucose levels. The beta cells of islets of Langerhans in the pancreas secrete a hormone called Insulin. Insulin is responsible for maintaining blood glucose levels. Too much or too little glucose in the blood can be a sign of a serious medical condition. High blood glucose levels(Hyperglycemia) may be a sign of diabetes, a disorder that can cause serious, long-term health conditions. Low blood glucose levels(Hypoglycemia) are common among people with type I diabetes and people with type II diabetes who take certain diabetes medicines. Without treatment, severely low blood sugar can lead to major health problems, including seizures and brain damage.

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There are two main types of blood glucose tests:

  • A healthcare expert draws a drop of blood, typically from a fingertip prick, for a capillary blood glucose test. These tests use a test strip and glucose metre (glucometer), which provide an instantaneous reading of your blood sugar level.
  • A blood sample is drawn from a vein by a phlebotomist for a venous (plasma) blood glucose test (venipuncture). Typically, a blood panel like a basic metabolic panel includes these glucose assays. The supplier will deliver the samples to a laboratory. Your samples will be prepared there by a medical laboratory scientist, who will also run the test on analysers.


blood glucose test

If there are symptoms of high blood glucose levels or low blood glucose levels, the health care provider may order a blood glucose test. Symptoms of high blood glucose levels include increased thirst and urination, blurred vision, weight loss, numbness or tingling in your feet or hands, fatigue, and wounds that won’t heal. 

Symptoms of low blood glucose levels include weakness, profuse sweating, irritability, confusion, unconsciousness, etc. 



Since testing is simple, therefore results are usually available quickly. Here are some of the methods of how to prepare for a blood glucose test:   

  1. Fasting 
  2. Random
  3. Oral Glucose Tolerance Test
  4. Post-prandial                                                                         

Fasting Blood Sugar Test

This measures your blood sugar level after fasting overnight(not eating). A fasting blood sugar level of 126 mg/dL or higher indicates you have diabetes, 100 to 125 mg/dL indicates you have prediabetes, and 99 mg/dL or lower is normal.                                  

Random Blood Sugar Test

This test is also known as Non-fasting Blood Sugar Test. This test is used to measure blood sugar at the time it is performed. You can take this test at any time and don’t need to fast (not eat) first. A blood sugar level of 200 mg/dL or higher indicates you have diabetes.

Oral Glucose Tolerance Test

This measures your blood sugar before and after you drink a liquid that contains glucose. This test requires fasting overnight and having your blood drawn to determine your fasting blood sugar level. The blood sugar level is checked 1 hour, 2 hours, and possibly 3 hours after drinking the liquid. At 2 hours, a blood sugar level of 200 mg/dL or higher indicates you have diabetes, 140 to 199 mg/dL indicates you have prediabetes, and 140 mg/dL or lower is considered normal.

Post-prandial Sugar Test

Two hours after the meal has begun, a test is administered to evaluate postprandial plasma glucose. When you have diabetes, this test is typically performed at home. It can assist you in determining whether you’re taking the appropriate dosage of insulin with meals. This test must be completed two hours after you begin eating a meal.



A phlebotomist will examine your arms as you sit in a chair to see if there is an accessible vein. After finding a vein, they will clean and sanitise the region. They will next use a tiny needle to draw blood from a vein in your arm. It might feel like a tiny pinch. A little blood is drawn once the needle has been inserted, and it is put in a test container. Once there is sufficient blood for testing, the needle will be taken out. To stop the bleeding, apply a cotton ball or piece of gauze to the area. Lastly, the area is covered with a bandage.                                                                                                                                                       


You’ll be asked which finger you’d like to use by a medical professional. Your fingertip will be pricked with a lancet and then infected with an alcohol swab. They will pinch the tip of your finger to create a blood drop. A blood drop will be applied to the test strip. once there is sufficient blood for the test. To stop the bleeding, place a cotton ball on the area. The glucometer will quickly display your blood glucose levels.                                                                                                                 


In some cases, people who are pregnant will develop high blood sugar during their pregnancy. This is called gestational diabetes. It is probably tested between 24 and 28 weeks of pregnancy. If your risk is higher for getting gestational diabetes (due to having more risk factors), your doctor may test you earlier. Blood sugar that’s higher than normal early in your pregnancy may indicate you have type 1 or type 2 diabetes rather than gestational diabetes.

Glucose Screening Test

This measures your blood sugar at the time when the test is performed. A normal result is 140 mg/dL or lower. If your level is higher than 140 mg/dL, you’ll need to take a glucose tolerance test.

Glucose Tolerance Test

This measures your blood sugar before and after you drink a liquid that contains glucose. You’ll fast (not eat) overnight before the test and have your blood drawn to determine the fasting blood sugar level. Then you’ll drink the liquid and have your blood sugar level checked for 1 hour, 2 hours, and possibly 3 hours afterwards. Results depend on how often your blood sugar is tested. Ask your doctor what your test results mean.

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