Blood Glucose: Fasting vs. Random

Synonyms:
Random Blood Glucose (RBG)
Random Blood Sugar (RBS)
Random glucose
Random sugar
Blood sugar
Blood glucose


Introduction

A blood glucose test measures the amount of a type of sugar, called glucose, in your blood.

The random glucose test is blood glucose level determined on a non fasting sample, taken randomly from a non fasting subject. This test is also called random blood glucose (RBG).

It assumes a recent meal and therefore has higher reference values than the fasting glucose test. The fasting glucose test is called fasting blood glucose (FBG) or fasting plasma glucose (FPG) since plasma is usually used for the determination of glucose, whether random or fasting.

Regulation of blood glucose

Glucose comes from carbohydrate foods (eg rice, pasta, bread, roti canai, mee goreng, pisang goreng, ubi, karipap, nasi lemak, etc). It is the main source of energy used by the body, and lasts 4 hours after normal food intake.

Glucose levels in the blood is controlled by insulin. Insulin is a hormone that helps the body's cells use the glucose found in the blood. Insulin is produced in the pancreas and released into the blood when the amount of glucose in the blood rises, for example, after you have eaten (postprandial).

Normally, your blood glucose levels increase slightly after you eat. This increase causes your pancreas to release insulin so that your blood glucose levels do not get too high (hyperglycaemia). Blood glucose levels that remain high over time can damage your eyes, kidneys, nerves, and blood vessels. These are referred to as complications of hyperglycemia, which occurs in long-standing diabetes or chronic diabetes.

Types of glucose determinations

There are several different types of blood glucose tests or glucose determinations. There are reasons why some tests are chosen over others. Some tests require fasting blood samples, while others do not and patients do not need to fast (as for random blood glucose).

1. Fasting blood sugar (FBS)
2. 2-hour postprandial (2HPP) blood sugar
3. Random blood sugar (RBS)
4. Oral glucose tolerance test (OGTT)
5. Glycohemoglobin A1c (HbA1c, A1c, A1C)

Why is blood glucose determined?

Blood glucose tests are done to:

1. Check for pre-diabetes and diabetes.
2. Monitor treatment of diabetes.
3. Check for diabetes that occurs during pregnancy (gestational diabetes).
4. Determine if an abnormally low blood sugar level (hypoglycemia) is present. A test to measure blood levels of insulin and a protein called C-peptide may be done along with a blood glucose test to determine the cause of hypoglycemia. To learn more, see the topic C-Peptide.

What is fasting blood glucose?

Fasting blood sugar (FBS) measures blood glucose after you have not eaten for at least 8 hours. It is often the first test done to check for pre-diabetes and diabetes.

What is 2HPP?

2-hour postprandial blood sugar measures blood glucose exactly 2 hours after you start eating a meal. This is not a test used to diagnose diabetes. It is part of a modified OGTT (see OGTT).

What are Normal Blood Glucose Levels?

The amount of glucose in your blood changes throughout the day and night. Your levels will change depending upon when, what and how much you have eaten, and whether or not you have exercised.

Normal Blood Sugars

A normal fasting (no food for eight hours) blood sugar level is between 70 and 99 mg/dL.
A normal blood sugar level two hours after eating is less than 140 mg/dL.

Reference values

The reference values for a "normal" random glucose test in an average adult are 79 - 140 mg/dl (4.4 - 7.8 mmol/L), between 140 - 200 mg/dl is considered pre-diabetes, and > 200 mg/dl is considered diabetes according to ADA guidelines (patients should visit the doctor or a clinic for additional tests. However, a random glucose of > 200 mg/dl does not necessarily mean patients are diabetic).

Conversion units for glucose

http://www.soc-bdr.org/conversion_glucose_mg_dl_to_mmol_l/index_en.html

What is hypoglycemia?

Hypoglycemia is low levels of glucose in blood.

A test to measure blood levels of insulin and a protein called C-peptide may be done along with a blood glucose test to determine the cause of hypoglycemia.

What to do when your blood glucose is too low.

You can eat 3 dried dates and drink some water to bring up your blood glucose levels. You can also drink glucose solution.

What is random blood glucose?

This test is also called a casual blood glucose test, but this term is hardly used.

Random blood sugar (RBS) measures blood glucose regardless of when you last ate.

Blood sample is taken randomly (untimed) from a non fasting patient. The patient does not have to fast when coming to the clinic or hospital.

Since blood glucose levels fluctuates throughout the day, several random measurements may be taken throughout the day.

Random testing is useful because glucose levels in healthy people do not vary widely throughout the day.

Blood glucose levels that vary widely may mean a problem.

What is pre-diabetes?

Pre-diabetes is a condition before full-fledged diabetes occurs. It is a temporary and transient period. It is a reversible condition and diabetes will disappear.

Patients who are diagnosed with pre-diabetes are at high risk of developing diabetes. You can prevent or delay diabetes by increasing physical activity, eating healthy foods, and maintaining or losing weight or obtaining normal weight.

What is impaired fasting glucose?

In pre-diabetes, patients have impaired fasting glucose levels. This means the cells in the body have become resistant and the cells can no longer take up glucose (glucose uptake becomes nil).

Pre-diabetes is also called impaired fasting glucose (IFG).

If left untreated IFG patients progress to become diabetic. At IFG stage, things are reversible. Pre-diabetes is reversible. Diabetes has no cure but it can be controlled.

How is pre-diabetes diagnosed?

Pre-diabetes is diagnosed by any one of the following:

1. A fasting blood glucose in between 100-125 mg/dL
2. An A1c between 5.7 - 6.4 percent
3. Any glucose value between 140 mg/dL and 199 mg/dL during a two-hour 75g oral glucose tolerance test. [The US uses 75g glucose load. We use 100g glucose load in Malaysia.]

What is an OGTT?

An oral glucose tolerance test (OGTT) is a series of blood glucose measurements taken after you drink a sweet liquid that contains glucose (eg 100g glucose mixed in a glass of water).

The OGTT is used to diagnose pre-diabetes and diabetes.

When is OGTT performed?

1. The OGTT is commonly used to diagnose diabetes that occurs during pregnancy (gestational diabetes or gestational diabetes mellitus, GDM). This test is not commonly used to diagnose diabetes in a person who is not pregnant. 
2. OGTT is also conducted with a hormone test (eg growth hormone, GH) in patients who have abnormally large features (gigantism, acromegaly). In acromegaly, OGTT is abnormal and glucose does not suppress the growth hormone levels.

What is a modified OGTT?

A modified OGTT is shorter and easier for doctors to do for their patients. 

A modified OGTT has only 2 values - before glucose intake and 2 hours after glucose intake (2HPP).

A 2HPP is part of a modified OGTT. 

How do you use glucose readings to diagnose diabetes?

Diabetes is diagnosed by ANY ONE of the following:

1. Two consecutive fasting blood glucose tests that are equal to or greater than 126 mg/dL
2. Any random blood glucose that is greater than 200 mg/dL
3. An A1c test that is equal to or greater than 6.5 percent. 
4. A two-hour oral glucose tolerance test with any value over 200 mg/dL
5. Sometimes you may have symptoms of fatigue, excessive urination or thirst, or unplanned weight loss. However, often people have no symptoms of high blood glucose and find a diabetes diagnosis surprising.

What is the criteria for diagnosing diabetes?

Criteria for Diagnosing Diabetes

(American Diabetes Association's criteria)

To be diagnosed with diabetes, you must meet one of the following criteria:

1. Have symptoms of diabetes (increased thirst, increased urination, and unexplained weight loss) and a blood sugar level equal to or greater than 200 milligrams per deciliter (mg/dL). The blood sugar test is done at any time, without regard for when you last ate (random plasma glucose test or random blood sugar test).
2. Have a fasting blood sugar level that is equal to or greater than 126 mg/dL. A fasting blood sugar test (fasting plasma glucose) is done after not eating or drinking anything but water for 8 hours.
3. Have a 2-hour oral glucose tolerance test (OGTT) result that is equal to or greater than 200 mg/dL. An OGTT is most commonly done to check for diabetes that occurs with pregnancy (gestational diabetes).
4. Have a hemoglobin A1c (HbA1c) that is 6.5% or higher.
5. The diagnosis of diabetes needs to be confirmed by repeating the same blood sugar test or doing a different test on another day.

What is A1c?

A1c is an easy blood test that gives a three month average of blood sugars. It indicates the amount of glycosylation that has occurred in the past 3 months. It tells the doctor whether patients controlled their diet or otherwise.

Glycohemoglobin A1c measures how much sugar (glucose) is stuck to red blood cells. 

This test can be used to diagnose diabetes.  

HbA1C or just A1C is an abbreviation for glycosylated hemoglobin. The blood levels of HbA1C can identify average blood glucose levels for an individual over approximately 120 days, the life span of a red blood cell.

It also shows how well your diabetes has been controlled in the last 2 to 3 months and whether your diabetes medicine needs to be changed.

What is normal A1c?

If patients controlled their blood glucose levels, HbA1c is less than 7%.
If patients did not control their blood glucose levels, HbA1c is greater than 7%.

What is eAG?

The result of your A1c test can be used to estimate your average blood sugar level. This is called your estimated average glucose, or eAG.


External links:
http://www.webmd.com/diabetes/blood-glucose
https://www.virginiamason.org/WhatareNormalBloodGlucoseLevels
http://en.wikipedia.org/wiki/Random_glucose_test
http://diabetescenter.blogspot.com/2008/07/renal-threshold-for-glucose.html