Glucose
Also known as:
Blood sugar; Fasting blood sugar; FBS; Fasting blood glucose; FBG;
Fasting plasma glucose; FPG; Blood glucose; Oral Glucose Tolerance Test;
OGTT; GTT; Urine glucose
Formal name: Blood Glucose; Urine Glucose
At a Glance
Why Get Tested?
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; to check for glucose in your urine
When to Get Tested?
Blood glucose: 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
Urine glucose: usually as part of a urinalysis
Urine glucose: usually as part of a urinalysis
Sample Required?
A blood sample drawn from a vein in your arm or a drop of blood from a skin prick; sometimes a random urine sample
is used. Some diabetic patients may use a continuous glucose monitor,
which is a small sensor wire inserted beneath the skin of the abdomen
that measures blood glucose every five minutes.
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.
The Test Sample
What is being tested?
This
test measures the amount of glucose in the blood or urine. 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.
If the blood glucose level drops too low, such as might occur in between meals or after a strenuous workout, glucagon (another pancreatic hormone) is secreted to induce the liver to turn some glycogen back into glucose, raising the blood glucose level. If the glucose/insulin feedback mechanism is working properly, the amount of glucose in the blood remains fairly stable. If the balance is disrupted and the glucose level in the blood rises, then the body tries to restore the balance, both by increasing insulin production and by eliminating excess glucose in the urine.
There are a few different conditions that may disrupt the balance between glucose and the pancreatic hormones, resulting in high or low blood glucose. The most common cause is diabetes. Diabetes is a group of disorders associated with insufficient insulin production and/or a resistance to insulin. People with untreated diabetes are not able to process and use glucose normally. Those who are not able to produce enough insulin to process glucose are diagnosed as having type1 diabetes while people who are resistant to insulin have type 2. Either type of diabetic may have acute and/or chronically increased blood glucose levels.
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.
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.
If the blood glucose level drops too low, such as might occur in between meals or after a strenuous workout, glucagon (another pancreatic hormone) is secreted to induce the liver to turn some glycogen back into glucose, raising the blood glucose level. If the glucose/insulin feedback mechanism is working properly, the amount of glucose in the blood remains fairly stable. If the balance is disrupted and the glucose level in the blood rises, then the body tries to restore the balance, both by increasing insulin production and by eliminating excess glucose in the urine.
There are a few different conditions that may disrupt the balance between glucose and the pancreatic hormones, resulting in high or low blood glucose. The most common cause is diabetes. Diabetes is a group of disorders associated with insufficient insulin production and/or a resistance to insulin. People with untreated diabetes are not able to process and use glucose normally. Those who are not able to produce enough insulin to process glucose are diagnosed as having type1 diabetes while people who are resistant to insulin have type 2. Either type of diabetic may have acute and/or chronically increased blood glucose levels.
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.
How is the sample collected for testing?
A
blood sample is obtained by inserting a needle into a vein in the arm or
a drop of blood is taken by pricking the skin, typically on a finger,
with a small, pointed lancet (fingerstick). Sometimes, a random urine sample
is collected. Some diabetics may use a continuous glucose monitor,
which is a small sensor wire inserted beneath the skin of the abdomen
and held in place with an adhesive patch. The sensor measures blood
glucose levels every five minutes and sends the results to a device that
is attached to the person's clothing. A digital readout on the device
lets the person know the blood glucose level in real time.
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.
The Test
How is it used?
The blood glucose test may be used to:
Screening
Blood glucose is often measured as part of a group of tests, such as a CMP (Comprehensive Metabolic Panel), 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 CMP 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). For this test, a woman is given a standard amount of a glucose solution to drink. After one hour, her glucose level is measured and if the level is higher than a defined value, then a longer OGTT (usually 2 or 3 hours) is performed to clarify the woman's status. This is the recommendation of the American Congress of Obstetricians and Gynecologists.
In 2011, the American Diabetes Association adopted guidelines that recommend changes in the way women are tested for gestational diabetes. Instead of the GCT described above, a 2-hour OGTT, using a 75-gram glucose drink, is performed. If one or more of her glucose levels at fasting, 1 hour, or 2 hours are above a certain level, then she is diagnosed as having gestational diabetes.
The ADA’s new recommendations follow those proposed in 2010 by the International Association of Diabetes and Pregnancy Study Group (IADPSG). This group based their recommendations on results of the Hyperglycemia and Adverse Pregnancy Outcome (HAPO) trial. This large study found that risk to babies increases with the gradual increase of maternal glucose levels; it determined that there is an increased risk of adverse outcomes for a baby even when only one of the mother’s glucose levels is below the cutpoints used to diagnose gestational diabetes, and slightly lowered some of the cutpoints from those used in older guidelines. (For more on this, read the article Panel Suggests New Criteria for Gestational Diabetes.)
Diagnosis
The American Diabetes Association recommends a fasting glucose or a different test, the hemoglobin A1c (A1c), 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. Another way to diagnose diabetes, especially if the screening test is not diagnostic, is the OGTT test. This test is a series of blood glucose tests. A fasting glucose is collected; then the person being tested drinks a standard amount of a glucose solution to "challenge" their system. This is followed by one or more additional glucose tests performed at specific intervals to track glucose levels over time.
In those with suspected hypoglycemia in which an initial FBG result is low, the glucose test is used as part of the "Whipple triad" to confirm a diagnosis. (See Common Questions #5).
Monitoring
Diabetics must monitor their own blood glucose levels, often several times a day, to determine how far above or below normal their glucose is and to determine what oral medications or insulin(s) they may need. This is usually done by placing a drop of blood from a skin prick onto a glucose strip and then inserting the strip into a glucose meter, a small machine that provides a digital readout of the blood glucose level.
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.
- Screen for both high blood glucose (hyperglycemia) and low blood glucose (hypoglycemia)
- Help diagnose diabetes
- Monitor glucose levels in persons with diabetes
Screening
Blood glucose is often measured as part of a group of tests, such as a CMP (Comprehensive Metabolic Panel), 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 CMP 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). For this test, a woman is given a standard amount of a glucose solution to drink. After one hour, her glucose level is measured and if the level is higher than a defined value, then a longer OGTT (usually 2 or 3 hours) is performed to clarify the woman's status. This is the recommendation of the American Congress of Obstetricians and Gynecologists.
In 2011, the American Diabetes Association adopted guidelines that recommend changes in the way women are tested for gestational diabetes. Instead of the GCT described above, a 2-hour OGTT, using a 75-gram glucose drink, is performed. If one or more of her glucose levels at fasting, 1 hour, or 2 hours are above a certain level, then she is diagnosed as having gestational diabetes.
The ADA’s new recommendations follow those proposed in 2010 by the International Association of Diabetes and Pregnancy Study Group (IADPSG). This group based their recommendations on results of the Hyperglycemia and Adverse Pregnancy Outcome (HAPO) trial. This large study found that risk to babies increases with the gradual increase of maternal glucose levels; it determined that there is an increased risk of adverse outcomes for a baby even when only one of the mother’s glucose levels is below the cutpoints used to diagnose gestational diabetes, and slightly lowered some of the cutpoints from those used in older guidelines. (For more on this, read the article Panel Suggests New Criteria for Gestational Diabetes.)
Diagnosis
The American Diabetes Association recommends a fasting glucose or a different test, the hemoglobin A1c (A1c), 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. Another way to diagnose diabetes, especially if the screening test is not diagnostic, is the OGTT test. This test is a series of blood glucose tests. A fasting glucose is collected; then the person being tested drinks a standard amount of a glucose solution to "challenge" their system. This is followed by one or more additional glucose tests performed at specific intervals to track glucose levels over time.
In those with suspected hypoglycemia in which an initial FBG result is low, the glucose test is used as part of the "Whipple triad" to confirm a diagnosis. (See Common Questions #5).
Monitoring
Diabetics must monitor their own blood glucose levels, often several times a day, to determine how far above or below normal their glucose is and to determine what oral medications or insulin(s) they may need. This is usually done by placing a drop of blood from a skin prick onto a glucose strip and then inserting the strip into a glucose meter, a small machine that provides a digital readout of the blood glucose level.
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.
When is it ordered?
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.
Screening with a glucose test may occur during public health fairs or as
part of workplace health programs. 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
- Sweating
- Hunger
- Trembling
- Anxiety
- Confusion
- Blurred Vision
Pre-diabetes is characterized by fasting or OGTT 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 A1c to monitor glucose control over time. Occasionally, a blood glucose level may be ordered along with insulin and C-peptide to evaluate insulin production.
Diabetics are often required to self-check their glucose, up to several times a day, to monitor glucose levels and to determine treatment options as prescribed by their doctor.
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.
What does the test result mean?
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.
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:
A low blood glucose level (hypoglycemia) may be seen with:
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.
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.
Fasting Blood Glucose
| Glucose Level | Indication |
|---|---|
| From 70 to 99 mg/dL (3.9 to 5.5 mmol/L) | Normal fasting glucose |
| From 100 to 125 mg/dL (5.6 to 6.9 mmol/L) | Impaired fasting glucose (pre-diabetes) |
| 126 mg/dL (7.0 mmol/L) and above on more than one testing occasion | Diabetes |
Oral Glucose Tolerance Test (OGTT)
| Glucose Level | Indication |
|---|---|
| Less than 140 mg/dL (7.8 mmol/L) | Normal glucose tolerance |
| From 140 to 200 mg/dL (7.8 to 11.1 mmol/L) | Impaired glucose tolerance (pre-diabetes) |
| Over 200 mg/dL (11.1 mmol/L) on more than one testing occasion | Diabetes |
Gestational Diabetes Screening: Glucose Challenge Test (as currently recommended by the American Congress of Obstetricians and Gynecologists)
| 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
| 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 | 180 mg/dL (10.0 mmol/L) | 180 mg/dL (10.0 mmol/L) |
| 2 hours after glucose load | 155 mg/dL (8.6 mmol/L) | 153 mg/dL (8.5 mmol/L) |
| 3 hours after glucose load | 140 mg/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. |
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 blood glucose level (hypoglycemia) may be seen with:
- Adrenal insufficiency
- Drinking excessive alcohol
- Severe liver disease
- Hypopituitarism
- Hypothyroidism
- Insulin overdose
- Insulinomas
- Starvation
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.
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.
Common Questions
Related Pages
On This Site
Conditions: Diabetes, Kidney Disease, Pancreatic Diseases, Thyroid Diseases, Cushing Syndrome
Screening: Diabetes - Children (2-12), Teens (13-18), Young Adults (19-29), Adults (30-49), Adults (50 and up)
In the News: Together, Two Tests Better Predictors of Progression to Diabetes (2011), Studies Evaluate A1c for Diagnosing Diabetes (2011), Use of A1c Point-of-Care Tests for Diabetes Screening Raises Concerns (2011), CDC and FDA Issue Alerts for Point-of-Care Testing (2010), Panel Suggests New Criteria for Gestational Diabetes (2010), ADA recommends A1c test to diagnose diabetes and pre-diabetes (2010), FDA issues alert about glucose monitoring test strips and meters (2009), Experts Recommend that Hemoglobin A1c also be used to Diagnose Diabetes (2009), Estimated Average Glucose: A New Term in Diabetes Control (2009)
Screening: Diabetes - Children (2-12), Teens (13-18), Young Adults (19-29), Adults (30-49), Adults (50 and up)
In the News: Together, Two Tests Better Predictors of Progression to Diabetes (2011), Studies Evaluate A1c for Diagnosing Diabetes (2011), Use of A1c Point-of-Care Tests for Diabetes Screening Raises Concerns (2011), CDC and FDA Issue Alerts for Point-of-Care Testing (2010), Panel Suggests New Criteria for Gestational Diabetes (2010), ADA recommends A1c test to diagnose diabetes and pre-diabetes (2010), FDA issues alert about glucose monitoring test strips and meters (2009), Experts Recommend that Hemoglobin A1c also be used to Diagnose Diabetes (2009), Estimated Average Glucose: A New Term in Diabetes Control (2009)
Elsewhere On The Web
College of American Pathologists: MyHealthTestReminder.com - Diabetes Tests
American Academy of Family Physicians: Diabetes - Blood tests to help manage your diabetes
Nemours Foundation: Blood test - Glucose
American Diabetes Association
American Association of Diabetes Educators: Patient Resources
Centers for Disease Control and Prevention: Diabetes Public Health Resource
National Institute of Diabetes and Digestive and Kidney Diseases: Diabetes
National Diabetes Education Program: Know your Blood Sugar Numbers
American Academy of Family Physicians: Diabetes - Blood tests to help manage your diabetes
Nemours Foundation: Blood test - Glucose
American Diabetes Association
American Association of Diabetes Educators: Patient Resources
Centers for Disease Control and Prevention: Diabetes Public Health Resource
National Institute of Diabetes and Digestive and Kidney Diseases: Diabetes
National Diabetes Education Program: Know your Blood Sugar Numbers
Article Sources
(Revised 2011 February). Know your Blood Sugar Numbers. National
Diabetes Education Program [On-line information]. PDF available for
download at http://ndep.nih.gov/media/knownumbers_eng.pdf through http://ndep.nih.gov. Accessed May 2011.
Olatunbosun, S. (Updated 2011 April 19). Glucose Intolerance. Medscape Reference [On-line information]. Available online at http://emedicine.medscape.com/article/119020-overview through http://emedicine.medscape.com. Accessed May 2011.
Dugdale, D. (Updated 2010 May 23). Glucose test – blood. MedlinePlus Medical Encyclopedia [On-line information]. Available online at http://www.nlm.nih.gov/medlineplus/ency/article/003482.htm. Accessed May 2011.
Olatunbosun, S. (Updated 2011 April 19). Glucose Intolerance. Medscape Reference [On-line information]. Available online at http://emedicine.medscape.com/article/119020-overview through http://emedicine.medscape.com. Accessed May 2011.
Dugdale, D. (Updated 2010 May 23). Glucose test – blood. MedlinePlus Medical Encyclopedia [On-line information]. Available online at http://www.nlm.nih.gov/medlineplus/ency/article/003482.htm. Accessed May 2011.
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