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To determine if your blood glucose level is within a healthy range; to screen for and diagnose diabetes and prediabetes and to monitor for high blood glucose (hyperglycemia) or low blood glucose (hypoglycemia); to check for glucose in your urine
Blood glucose: when you are older than 45 years or have risk factors for diabetes; when you have symptoms suggesting high or low blood glucose; during pregnancy; when you are diabetic, self-checks up to several times a day to monitor blood glucose levels
Urine glucose: usually as part of a urinalysis
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 diabetics may use a continuous glucose monitor, which uses a small sensor wire inserted beneath the skin of the abdomen to measure blood glucose at frequent intervals and provides a result.
In general, it is recommended that you fast (nothing to eat or drink except water) for at least 8 hours before having a blood glucose test. For people 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 health practitioner's instructions.
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. A few different protocols may be used to evaluate the glucose level in the blood. See "How is it used?" under Common Questions for more information on these. Sometimes, glucose may be tested in urine.
During digestion, fruits, vegetables, breads and other dietary sources of 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 the effects of insulin. People with untreated diabetes are not able to process and use glucose normally. Those who are not able to produce any or enough insulin (and typically have diabetes autoantibodies) are diagnosed as having type 1 diabetes. Those who are resistant to insulin and may or may not be able to produce sufficient quantities of it may have prediabetes or type 2 diabetes.
Severe, acute changes in blood glucose, either high or low, 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 gestational diabetes, which is hyperglycemia that occurs during pregnancy. 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.
A blood sample is obtained by inserting a needle into a vein in the arm or a drop of blood is taken by pricking a finger with a small, pointed lancet (fingerstick). Sometimes, a random urine sample is collected. Some diabetics may use a continuous glucose monitor, which uses 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 at frequent intervals 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.
For screening purposes, fasting is generally recommended (nothing to eat or drink except water) for at least 8 hours before a blood glucose test. Those who have been diagnosed with diabetes and are monitoring their glucose levels are often tested both while fasting and after meals. For random and timed tests, follow the health practitioner's instructions. A glucose tolerance test requires that the person 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 blood glucose test may be used to:
A few different testing protocols may be used to evaluate blood glucose levels, depending on the purpose.
Screening and Diagnosis
The following tests may be used for screening and diagnosis of type 1, type 2 or prediabetes. (Gestational diabetes testing is different—see below.) If the initial screening result from one of the tests is abnormal, the test is repeated on another day. The repeat result must also be abnormal to confirm a diagnosis of diabetes.
Sometimes a blood sample may be drawn and glucose measured when a person has not been fasting, for example, when a comprehensive metabolic panel (CMP) is performed. If the result is abnormal, it is typically followed up with a fasting blood glucose test or a GTT.
Glucose blood tests are also used to screen pregnant women for gestational diabetes between their 24th and 28th week of pregnancy. The American Diabetes Association and the U.S. Preventive Services Task Force recommend that pregnant women not previously known to have diabetes be screened and diagnosed, using either a one-step or two-step approach. The American College of Obstetricians and Gynecologists (ACOG) recommends the two-step approach.
Glucose testing is also used to test women who were diagnosed with gestational diabetes 6-12 weeks after they have delivered their baby to detect persistent diabetes.
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 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. The health practitioner may follow up an elevated urine glucose test with blood glucose testing. Urine glucose testing is a screening tool, but it is not sensitive enough for diagnosis or monitoring.
Other tests, such as diabetes autoantibodies, insulin, and C-peptide, may sometimes be performed along with these tests to help determine the cause of abnormal glucose levels, to distinguish between type 1 and type 2 diabetes, and to evaluate insulin production.
Several health organizations, including the American Diabetes Association (ADA) and the U. S. Preventive Services Task Force (USPSTF), recommend diabetes screening when a person is age 45 or older or when a person of any age has risk factors. Examples of risk factors include:
If the screening test result is within normal limits, the ADA recommends retesting within 3 years, while the USPSTF recommends yearly testing. People with prediabetes may be monitored with annual testing.
See the screening articles for Children, Teens, Young Adults, Adults and Adults 50 and Up for additional details.
A blood glucose test may also be ordered when someone has signs and symptoms of high blood glucose, such as:
or symptoms of low blood glucose, such as:
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 health practitioner. The healthcare provider may order blood glucose levels periodically in conjunction with other tests such as A1c to monitor glucose control over time.
Pregnant women are usually screened for gestational diabetes between their 24th and 28th week of pregnancy, unless they have early symptoms or have had gestational diabetes with a previous pregnancy. A woman may be tested earlier in her pregnancy if she is at risk of type 2 diabetes (overt diabetes), says the ADA. When a woman has type 1, type 2 or gestational diabetes, her health practitioner will usually order glucose levels throughout the rest of her pregnancy and after delivery to monitor her condition.
High levels of glucose most frequently indicate diabetes, but many other diseases and conditions can also cause elevated blood glucose.
In a person with signs and symptoms of diabetes or high blood glucose, a non-fasting glucose level (random blood sample) that is equal to or greater than 200 mg/dL (11.1 mmol/L) indicates diabetes.
The following information summarizes the meaning of other test results.
|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)||Prediabetes (impaired fasting glucose)|
|126 mg/dL (7.0 mmol/L) and above on more than one testing occasion||Diabetes|
|Less than 140 mg/dL (7.8 mmol/L)||Normal glucose tolerance|
|From 140 to 199 mg/dL (7.8 to 11.1 mmol/L)||Prediabetes (impaired glucose tolerance)|
|Equal to or greater than 200 mg/dL (11.1 mmol/L) on more than one testing occasion||Diabetes|
|Time of sample collection||glucose level|
|Fasting||Equal to or greater than 92 mg/dL (5.1 mmol/L)|
|1 hour||Equal to or greater than 180 mg/dL (10.0 mmol/L)|
|2 hour||Equal to or greater than 153 mg/dL (8.5 mmol/L)|
|Less than 140* mg/dL (7.8 mmol/L)||Normal screen|
|140* mg/dL (7.8 mmol/L) and over||Abnormal, needs OGTT (see Step two below)|
*Some experts recommend 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). ACOG recommends a lower threshold of 135 mg/dL (7.5 mmol/L) in high-risk ethnic groups with higher prevalence of gestational diabetes.
|Time of sample collection||target levels**|
|Fasting (prior to glucose load)||95 mg/dL (5.3 mmol/L)|
|1 hour after glucose load||180 mg/dL (10.0 mmol/L)|
|2 hours after glucose load||155 mg/dL (8.6 mmol/L)|
|3 hours after glucose load||140 mg/dL (7.8 mmol/L)|
**Some labs may use different numbers.
Some other diseases and conditions that can result in an elevated blood glucose level include:
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.
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. Some people naturally leak glucose in their urine when blood levels are normal. Some medications used to treat diabetes work by increasing the elimination of glucose in the urine.
Extreme stress can cause a temporary rise in blood glucose. This can be a result of, for example, trauma, surgery, heart attack or stroke.
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.
If you are not diabetic or prediabetic, there is usually no reason to test glucose levels at home. Screening done as part of your regular physical should be sufficient.
If you have been diagnosed with diabetes or gestational diabetes, however, your health practitioner or diabetes educator will recommend a home glucose monitor (glucometer, or one of the newer methods that use very tiny amounts of blood or tests the interstitial fluid -- the fluid between your cells -- for glucose). You will be given guidelines for how high or low your blood sugar should be at different times of the day. By checking your glucose regularly, you can see if the diet and medication schedule you are following is working properly for you.
Not in most cases. Glucose will usually only show up in the urine if it is at sufficiently high levels in the blood so that the body is "dumping" the excess into the urine, or if there is some degree of kidney damage and the glucose is leaking out into the urine. Urine glucose, however, is sometimes used as a rough indicator of high glucose levels and the urine indicator strip (dipstick) that measures the glucose is occasionally useful for tracking the presence of protein and ketones in the urine.
For type 2 diabetes, which is the most common type of diabetes, losing excess weight, eating a healthy diet that is high in fiber and restricted in carbohydrates, and getting regular amounts of exercise may be enough to lower your blood glucose levels. In many cases, however, oral medications that increase the body's secretion of and sensitivity to insulin are necessary to achieve the desired glucose level. With type 1 diabetes (and with type 2 diabetes that does not respond well enough to oral medications), insulin injections several times a day are necessary. See the article on Diabetes for more on treatment.
If you are diabetic, a diabetic educator (often a nurse with specialized training) can make sure that you know how to:
An actual diagnosis of hypoglycemia requires satisfying the "Whipple triad." These three criteria include:
Primary hypoglycemia is rare and often diagnosed in infancy. People may have symptoms of hypoglycemia without really having low blood sugar. In such cases, dietary changes such as eating frequent small meals and several snacks a day and choosing complex carbohydrates over simple sugars may be enough to ease symptoms.
Table sugar (sucrose) is a combination of two simple sugars, glucose and fructose, that are both released when table sugar is digested. Because glucose is the body's primary energy source, the blood glucose test is often informally referred to as a "blood sugar" test.
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