Plasma Glucose (Fasting)

Specimen Required

Sodium Fluoride Vial (Sugar Vial)

Fasting Required

This test requires fasting before sample collection.

Purpose of the Test

To determine whether or not your blood glucose level is within normal ranges; to screen for, diagnose, and monitor diabetes, and to monitor for the presence of hypoglycaemia (low blood glucose) and hyperglycaemia (high blood glucose)

When this test is required

Fasting blood glucose testing may be requested as part of a routine examination especially in those people at high risk of developing diabetes.The risk factors are: Those with a strong family history of diabetes (first degree relative) Those who are overweight and obese High risk ethnicity/race (more prevalent among South Asian, Chinese, African-Caribbean and black African than white population) People with other health conditions (those who have had myocardial infarction or a stroke, poly cystic ovary syndrome (PCOS) or have a history of gestational diabetes) People with mental health conditions or learning disabilities People taking certain drugs such as steroids, anti-retroviral and some antipsychotic drugs Previous impaired glucose tolerance, impaired fasting glucose or elevated HbA1cThere are different risk scores available to identify those at risk of developing diabetes. The fasting blood glucose test may also be used to help diagnose diabetes when someone has symptoms of hyperglycaemia such as: Increased thirst Increased urination Urinary tract infections Tiredness Blurred vision Slow-healing infectionsBlood glucose may also be tested when a person has symptoms of hypoglycaemia, such as: Sweating Hunger Trembling Anxiety Confusion Blurred VisionGlucose testing is also done in emergency settings to determine if low or high glucose is contributing to symptoms such as fainting and unconsciousness.

What the Test Detects

Glucose is a simple sugar that serves as the main source of energy for the body. The carbohydrates we eat are broken down into glucose (and a few other simple sugars), absorbed by the small intestine and circulated throughout the body. Most of the body’s cells require glucose for energy production; the brain and nervous system cells rely on glucose for energy, and can only function when glucose levels in the blood remain within a…Glucose is a simple sugar that serves as the main source of energy for the body. The carbohydrates we eat are broken down into glucose (and a few other simple sugars), absorbed by the small intestine and circulated throughout the body. Most of the body’s cells require glucose for energy production; the brain and nervous system cells rely on glucose for energy, and can only function when glucose levels in the blood remain within a certain range. The body’s use of glucose depends on the availability of insulin, a hormone produced by the pancreas. Insulin acts to control the transport of glucose into the body’s cells to be used for energy. Insulin also directs the liver to store excess glucose as glycogen for short term energy storage and promotes the synthesis of fats, which form the basis of a longer term store of energy. Normally, blood glucose levels rise slightly after a meal, and insulin is released to lower them, with the amount of insulin released dependent upon the size and content of the meal. If blood glucose levels drop too low, such as might occur between meals or after a strenuous exercise, glucagon (another hormone from the pancreas) is produced to tell the liver to release some of its glucose stores, raising the blood glucose levels. If the glucose/insulin system is working properly the amount of glucose in the blood remains fairly stable. Hyperglycaemia and hypoglycaemia, caused by a variety of conditions, are both hard on the body. Severe, sudden high or low blood glucose levels can be life threatening, causing organ failure, brain damage, coma, and, in extreme cases, death. Long-term high blood glucose levels can cause progressive damage to body organs such as the kidneys, eyes, blood vessels, heart and nerves. Untreated hyperglycaemia that arises during pregnancy (known as ‘gestational diabetes’) can cause mothers to give birth to large babies who may have low glucose levels following birth. See MoreSee Less

Preparation for the Test

For screening purposes, fasting is generally recommended (nothing to eat or drink except water) for at least 8 hours (generally 8-10 hours fasting) 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 instructions given to you by your healthcare professional.There is another test called an oral glucose tolerance test (OGTT). It requires that the person fasts (as described above) for the first blood sample and then drink a liquid containing a specified amount of glucose; a further blood sample is then taken after 2 hours. This test is commonly offered to pregnant patients for diagnosis of diabetes in pregnancy (gestational diabetes).

Sample Requirements

A blood sample taken from a vein in your arm or, for self-monitoring, a drop of blood from your finger. A few 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.

Additional Notes

Hypoglycaemia is characterised 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). An actual diagnosis of hypoglycaemia requires satisfying the following three criteria: Documented low glucose levels (the cut offs vary depending on the age of the person and where the sample was taken from) Symptoms of hypoglycaemia Reversal of the symptoms when blood glucose levels are returned to normal.In some people with symptoms of low blood glucose, dietary changes such as eating frequent small meals and several snacks a day and choosing complex carbohydrates over simple sugars may be enough to help. Those with fasting hypoglycaemia may require IV (intravenous) glucose, if dietary measures are insufficient.It should be remembered that the glucose level in a finger drops as the hand gets colder (as blood supply slows down) therefore in people who have fainted (and therefore have poor blood supply to their limbs also) low glucose can be detected on finger pricks. This does not mean however that the reason for the collapse was low blood glucose levels.

Selected Tests