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For information on other types of glucose tests, see Glucose Tolerance Test, Glucose Tests for Gestational Diabetes, and urine glucose (Urinalysis).
Glucose (commonly called "blood sugar") is the primary energy source for the body's cells and the only short-term 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. Glucose tests measure the level of glucose in your blood or detect glucose in your urine.
A few different protocols may be used to evaluate glucose levels. This article focuses on:
Other types of glucose tests include:
During digestion, the carbohydrates that you eat are broken down into glucose (and other nutrients). They are absorbed by the digestive tract, move into the blood, and circulate throughout the body. Normally, blood glucose rises slightly after a meal and the hormone insulin is released by the pancreas into the blood in response. The amount of insulin released corresponds to the size and content of the meal. Insulin helps transport glucose into the body's cells, where it is used for energy. As glucose moves into the cells and is broken down (metabolized), the blood glucose level drops and the pancreas responds by decreasing the release of insulin.
If this glucose/insulin blood feedback system is working properly, the amount of glucose in the blood remains fairly stable. If the feedback system is disrupted and the glucose level in the blood rises, then the body tries to restore the balance by increasing insulin production.
Diabetes is the most common disease resulting from an imbalance between glucose and insulin.
Severe, acute changes in blood glucose, either high (hyperglycemia) or low (hypoglycemia), can be life-threatening, causing organ failure, brain damage, coma, and, in some cases, death. Chronically high blood glucose levels that can occur with untreated or poorly controlled diabetes 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.
Screening and Diagnosis
Some people with diabetes 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 medications or insulin(s) they may need. Glucose monitoring may be done by inserting a glucose test strip into a small instrument called a glucose meter. A drop of blood from a skin prick is placed onto the test strip and the glucose meter provides a digital readout of the blood glucose level. Alternatively, some people may use a continuous glucose monitoring device.
Screening and Diagnosis
The American Diabetes Association (ADA) recommends diabetes screening when you are age 45 or older. Several health organizations, including the ADA, recommend screening when you have risk factors, regardless of age. You may be at risk if you:
The U.S. Preventive Services Task Force (USPSTF) recommends screening for abnormal blood glucose as part of a risk assessment for cardiovascular disease in adults ages 40 to 70 who are overweight or obese.
If the screening test result is within normal limits, the ADA and USPSTF recommend rescreening every 3 years. People with prediabetes may be monitored with annual testing.
A blood glucose test may also be ordered when you have signs and symptoms of abnormal blood glucose levels.
High blood glucose (hyperglycemia):
Low blood glucose (hypoglycemia):
If you have diabetes, you may be instructed to self-check your glucose levels up to several times a day. Your healthcare practitioner may order blood glucose levels periodically in conjunction with other tests such as hemoglobin A1c to monitor glucose control over time.
Screening and Diagnosis
High levels of glucose most frequently indicate diabetes, but many other diseases and conditions can also cause elevated blood glucose.
A random glucose level (non-fasting) in a person with signs and symptoms of diabetes and hyperglycemia that is equal to or greater than 200 mg/dL (11.1 mmol/L) indicates diabetes.
The following table summarizes the meaning of fasting glucose 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|
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. (See "How is hypoglycemia diagnosed?" below.)
A low blood glucose level (hypoglycemia) may be seen with:
If you have diabetes and are monitoring your glucose levels, your healthcare practitioner will give you guidelines for how high or low your blood sugar should be at different times of the day. This may depend on several factors, such as:
No, fingerstick blood samples are not appropriate for diagnosing diabetes. Rather, a blood sample drawn from a vein should be used for diagnostic testing. However, fingerstick samples may be used to monitor your glucose levels if you have been diagnosed with diabetes.
You may have non-fasting glucose testing in certain situations:
Your healthcare practitioner will discuss with you whether you need to monitor your glucose levels. Not everyone with type 2 diabetes needs to monitor their glucose levels every day, especially if they are able to manage their diabetes and glucose levels with diet and exercise.
However, some people with type 2 diabetes must check their blood glucose levels, sometimes several times a day. This may be done using a glucose meter. You would place a drop of blood from a skin prick onto a glucose strip and then insert the strip into the glucose meter, a small machine that provides a digital readout of the blood glucose level. Alternatively, some people may use a continuous glucose monitoring device.
Your healthcare practitioner will give you 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.
If you have not been diagnosed with diabetes or prediabetes, 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, however, your healthcare practitioner or diabetes educator may recommend a home glucose monitor (glucometer or continuous glucose monitoring device) so that you can test your blood glucose levels at home. By checking your glucose regularly, you can see if the diet and medication schedule you are following is working properly for you.
Urine samples are routinely tested for glucose as part of a urinalysis. Additional testing is usually done to identify the cause of an abnormal urine glucose result.
Glucose usually only shows up in the urine if glucose is at sufficiently high levels in the blood that some of the excess is lost in the urine, or if there is some degree of kidney damage and the glucose is leaking out into the urine.
Yes, but the purpose and meaning of results are different for each type of fluid. For more details see the article Body Fluid Testing with links to related articles.
Hemoglobin A1c is an indicator of long-term glucose control that is commonly ordered in patients with prediabetes and diabetes and can also be used as a screening test. Other less common tests, such as islet 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.
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, medications may be 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.
A diabetes educator (often a nurse with specialized training) can make sure that you know how to:
A medical diagnosis of hypoglycemia typically 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.
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