Test Library

To determine if your blood glucose level is within a healthy range;

To screen for, diagnose, and monitor high blood glucose (hyperglycemia) or low blood glucose hypoglycemia), diabetes, and pre-diabetes;

as part of a regular physical, when you have symptoms suggesting hyperglycemia or hypoglycemia, and during pregnancy;
if you are diabetic, self-checks up to several times a day to monitor blood glucose levels

Blood glucose testing can be used to screen healthy, asymptomatic individuals for diabetes and pre-diabetes because diabetes is a common disease that begins with few symptoms. It may also be ordered when someone has a routine physical exam. Screening is especially important for people at high risk of developing diabetes, such as those with a family history of diabetes, those who are overweight, and those who are more than 40 to 45 years old.

The glucose test may also be ordered to help diagnose diabetes when someone has symptoms of high blood glucose (hyperglycemia), such as:

• Increased thirst, usually with frequent urination
• Fatigue
• Blurred vision
• Slow-healing infections

or symptoms of low blood glucose (hypoglycemia), such as:

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

Blood glucose testing is also done in emergency settings to determine if low or high glucose is contributing to symptoms such as fainting and unconsciousness.

Pre-diabetes is characterized by fasting levels that are higher than normal but lower than those defined as diabetic. The doctor may order a glucose test at regular intervals to monitor the person’s status.

With known diabetics, doctors will order glucose levels periodically in conjunction with other tests such as HbA1c to monitor glucose control over time. Occasionally, a blood glucose level may be ordered along with insulin and C-peptide to evaluate insulin production.

Pregnant women are usually screened for gestational diabetes late in their pregnancies, unless they have early symptoms or have had gestational diabetes with a previous pregnancy. When a woman has gestational diabetes, her doctor will usually order glucose levels throughout the rest of her pregnancy and after delivery to monitor her condition.

A blood sample drawn from a vein in your arm.

Test Preparation Needed?

In general, it is recommended that you fast – nothing to eat or drink except water – 8 hours before having a blood glucose test. In persons with diabetes, glucose levels are often checked both while fasting and after meals to provide the best control of diabetes. For random, timed, and post-meal glucose tests, follow your doctor’s instructions.

Fasting Glucose – 8 Hours Fasting

Post Prandial Glucose – 2 Hours After meal,

This test measures the amount of glucose in the blood. Glucose is the primary energy source for the body’s cells and the only energy source for the brain and nervous system. A steady supply must be available for use, and a relatively constant level of glucose must be maintained in the blood.

During digestion, fruits, vegetables, breads and other carbohydrates are broken down into glucose (and other nutrients); they are absorbed by the small intestine and circulated throughout the body. Using glucose for energy production depends on insulin, a hormone produced by the pancreas. Insulin facilitates transport of glucose into the body’s cells and directs the liver to store excess energy as glycogen for short-term storage and/or as triglycerides in adipose (fat) cells.

Normally, blood glucose rises slightly after a meal and insulin is released by the pancreas into the blood in response, with the amount corresponding to the size and content of the meal. As glucose moves into the cells and is metabolized, the level in the blood drops and the pancreas responds by slowing, then stopping the release of insulin.

Severe, acute high blood glucose (hyperglycemia) or low blood glucose (hypoglycemia) can be life-threatening, causing organ failure, brain damage, coma, and, in extreme cases, death. Chronically high blood glucose levels can cause progressive damage to body organs such as the kidneys, eyes, heart and blood vessels, and nerves. Chronic hypoglycemia can lead to brain and nerve damage.

Some women may develop hyperglycemia during pregnancy, which is termed gestational diabetes. If untreated, this can cause these mothers to give birth to large babies who may have low glucose levels. Women who have had gestational diabetes may or may not go on to develop diabetes.

Sample Collection Procedure

Is any test preparation needed to ensure the quality of the sample?

For screening purposes, fasting is generally recommended – nothing to eat or drink except water – at least 8 hours before a blood glucose test.

Those who have been diagnosed with diabetes and are monitoring glucose levels are often tested both while fasting and after meals.

For random and timed tests, follow the doctor’s instructions. A glucose tolerance test requires that you fast for the first blood sample and then drink a liquid containing a specified amount of glucose. Subsequent blood samples are drawn at specified times.

How is it used?

The blood glucose test may be used to:

• Screen for both high blood glucose (hyperglycemia) and low blood glucose (hypoglycemia)
• Help diagnose diabetes
• Monitor glucose levels in persons with diabetes

Depending on the purpose of testing, glucose may be measured on a fasting basis (collected after an 8- to 10-hour fast), randomly (anytime), post prandial (after a meal), and/or as part of an oral glucose challenge or tolerance test (OGTT / GTT).

Screening

Blood glucose is often measured as part of a group of tests, such as a Comprehensive Check Up during routine physicals. This is done to screen for diabetes, which often causes no symptoms early in its course, and for pre-diabetes – moderately increased blood glucose levels that indicate an increased risk of developing type 2 diabetes.

For screening purposes, a Comprehensive Medical Check Up or blood glucose test is performed on a fasting basis (fasting blood glucose, FBG).

Many pregnant women are screened for gestational diabetes, a temporary form of hyperglycemia, between their 24th and 28th week of pregnancy using a version of the OGTT, a 1-hour glucose challenge (GCT).

Diagnosis

The American Diabetes Association recommends a fasting glucose or a different test, the hemoglobin A1c (HbA1c), to diagnose diabetes but says that testing should be done twice, at different times, preferably with the same test in order to confirm a diagnosis of diabetes.

Monitoring

Diabetics must monitor their own blood glucose levels, often several times, to determine how far above or below normal their glucose is and to determine what oral medications or insulin(s) they may need.

Urine

Urine glucose is one of the substances tested when a urinalysis is performed. A urinalysis may be done routinely as part of a physical or prenatal checkup, when a doctor suspects that a person may have a urinary tract infection or for a variety of other reasons. The doctor may follow up an elevated urine glucose test with blood glucose testing.

 

Blood Glucose

High levels of glucose most frequently indicate diabetes, but many other diseases and conditions can also cause an elevated blood glucose. The following information summarizes the meaning of the test results. These are based on the clinical practice recommendations of the American Diabetes Association.

Gestational Diabetes Screening: Glucose Challenge Test (as currently recommended by the American Congress of Obstetricians and Gynecologists)

Sample drawn 1 hour after a 50-gram glucose drink.
GLUCOSE LEVEL	INDICATION
Less than 140* mg/dL (7.8 mmol/L)	Normal screen
140* mg/dL (7.8 mmol/L) and over	Abnormal, needs OGTT (see below)
* Some use a cutoff of 130 mg/dL (7.2 mmol/L) because that identifies 90% of women with gestational diabetes, compared to 80% identified using the threshold of 140 mg/dL (7.8 mmol/L).

Gestational Diabetes Diagnostic: OGTT

In 2011,the American Diabetes Association adopted new guidelines that recommend a 2-hour glucose tolerance test rather than a 3-hour OGTT as still recommended by the American Congress of Obstetricians and Gynecologists. Details from both are included below.

TIME OF SAMPLE COLLECTION	CURRENT ACOG TARGET LEVEL	ADA TARGET LEVEL
	Glucose load: Samples drawn after 100-gram glucose drink	Glucose load: Samples drawn after 75-gram glucose drink
Fasting(prior to glucose load)	95 mg/dL(5.3 mmol/L)	92 mg/dL(5.1 mmol/L)
1 hour after glucose load	180mg/dL (10.0 mmol/L)	180mg/dL (10.0 mmol/L)
2 hours after glucose load	155mg/dL (8.6 mmol/L)	153mg/dL (8.5 mmol/L)
3 hours after glucose load	140mg/dL (7.8 mmol/L)	Not applicable
Results interpretation	If TWO or more values meet or exceed the target level, gestational diabetes is diagnosed.	If ONE or more values meet or exceed the target level, gestational diabetes is diagnosed.

Moderately increased blood glucose levels may be seen in those with pre-diabetes. Left un-addressed, pre-diabetes increases the risk of developing type 2 diabetes.

Some other diseases and conditions that can result in an elevated blood glucose level include:

• Acromegaly
• Acute stress (response to trauma, heart attack, and stroke for instance)
• Chronic kidney failure
• Cushing syndrome
• Excessive food intake
• Hyperthyroidism
• Pancreatic cancer
• Pancreatitis

A low level of glucose may indicate hypoglycemia, a condition characterized by a drop in blood glucose to a level where first it causes nervous system symptoms (sweating, palpitations, hunger, trembling, and anxiety), then begins to affect the brain (causing confusion, hallucinations, blurred vision, and sometimes even coma and death). A diagnosis of hypoglycemia uses three criteria known as the Whipple triad. (See the common questions section.).

A low blood glucose level (hypoglycemia) may be seen with:

• Adrenal insufficiency
• Drinking excessive alcohol
• Severe liver disease
• Hypopituitarism
• Hypothyroidism
• Insulin overdose
• Insulinomas
• Starvation

Urine Glucose

Low to undetectable urine glucose results are considered normal. Any condition that raises blood glucose such as diabetes or the other conditions listed above also has the potential to elevate the concentration of glucose in the urine.

Increased urine glucose may be seen with medications, such as estrogens and chloral hydrate, and with some forms of kidney disease.

Is there anything else I should know?

Extreme stress can cause a temporary rise in blood glucose. This can be a result of trauma, surgery, heart attack or stroke, for example.

Drugs, including corticosteroids, tricyclic antidepressants, diuretics, epinephrine, estrogens (birth control pills and hormone replacement), lithium, phenytoin, and salicylates, can increase glucose levels, while drugs such as acetaminophen and anabolic steroids can decrease levels.