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justaguide eNotes educator| Certified Educator

The presence of glucose can be detected with Benedict's reagent.

Benedict's reagent is prepared by mixing 100 g of anhydrous sodium carbonate, 173 g of sodium citrate and 17.3 g of copper(II) sulfate pentahydrate.

All reducing sugars, a list that includes glucose, can be detected using Benedict's reagent.

The test consists of dissolving the sample that needs to be tested for glucose in water. A small amount of Benedict's solution is added to the test solution and the mixture is placed in a water bath for around 5 minutes. If glucose is present in the sample the color of the solution changes color from blue to brick red.

ssarfraz | Student


Glucose is the primary energy source for the body’s cells and the only energy source for the brain and nervous system.

Glucose is the most important carbohydrate; the major metabolic fuel of mammals (except ruminants) and a universal fuel of the Fetus.

where as, carbohydrates are widely distributed in plants and animals; they have important structural and metabolic role.


This test measures the amount of glucose in the blood or urine. 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. 

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 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.

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.

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.

When is it ordered?

The glucose test may also be ordered to help diagnose diabetes when someone has symptoms of high blood glucose, 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.

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.

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)

Levels applicable except during pregnancy. Sample drawn 2 hours after a 75-gram glucose drink. 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)

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 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 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:

  • 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.

mrfushiman | Student

Also, in addition, complex carbohydrates can be determined by iodine solution

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