Blood Glucose Tests

Blood glucose, also called blood sugar, is the amount of glucose circulatingin the blood. Glucose is a type of sugar. The body forms glucose when it breaksfoods that a person eats down into a useable form of energy. Glucose is a mainenergy source for the body.

Measuring the amount of blood glucose in the blood helps evaluate:

how the body is converting and breaking foods down into energy

how the liver is working

how the organs in the body that help regulate blood glucose are working

Blood glucose can be measured in a number of ways. Some of thetests that can measure blood glucose include:

fasting blood glucose test

glycosylated hemoglobin,also called HbA1c or hemoglobin A1c test

oral glucose tolerance test

random blood glucose test

self-monitoring of blood glucose, also called SMBG, or homeblood glucose monitoringtests

Who is a candidate for the test?

A doctor may order a blood glucose test to evaluatethe amount of glucose in the blood when he or she suspects a person hasdiabetes.These tests may also be done to rule out other causes of high or low blood glucose.

How is the test performed?

Here’s how some of the tests may be done to check blood glucoselevels:

A fasting blood glucose test is the preferred method to diagnosediabetesand rule out other conditions. This test is done after a person has had nothing toeat or drink except water for at least 8 hours. This is often called fasting. It isgenerally started overnight so the test can be done in the morning. Normal fastingplasma glucose levels are less than 110 mg/dL (milligrams per deciliter). Fasting plasma glucose levels ofmore than 126 mg/dL on two or more tests done on different days usually indicatediabetes.Levels between 110 and 126 indicate a condition known as pre-diabetes.

An HbA1c, also known as glycosylated hemoglobin,measures the average blood glucose over the past 3 months. It is a goodmeasure of long-term blood glucose control. This test is generally done only inpeople who have diabetes. It is used to assess how well their therapy is working.

An oral glucose tolerance test requires a person to drink a premeasured amount of aglucose drink. Then two hours later, a blood glucose measurement is done. Healthyglucose levels with this test are less than 140 mg/dL. If the blood glucose isgreater than 200 mg/dL, then another test is done on a different day to confirm whetherthe person has diabetesor not. Usually the fasting blood glucose test or the random glucose test is done.

A random blood glucose test is done shortly after a person has eatenor had something to drink. A level of 200 mg/dL or highermay indicate diabetes.Usually if a level is above 200 mg/dL, a fasting glucose test or oralglucose tolerance testis done to confirm the diagnosis of diabetes.

A self-monitoring of blood glucose, also called SMBG or home blood glucose monitoring,lets a person monitor blood glucose at home. This is done only by people who havediabetes.A record of daily blood glucose readings can be kept to follow changes in glucoselevels throughout the day. This can be useful to the doctor in deciding if changes need tobe made to the person’s diabetes treatment plan.

For most blood glucose tests, a blood sample is taken from a vein inthe arm. First, the skin over the vein is cleaned with an antiseptic. A thin stripof rubber called a tourniquet is wrapped around the upper arm to enlarge the veins.A small needle is gently inserted into the enlarged vein. Then blood is collectedfor testing in the laboratory. After the tourniquet is removed, a cotton ball is heldover the needle site until bleeding stops. The laboratory then tests the bloodsample.

The home blood glucose monitoringsystem, on the other hand, uses a small drop of blood from a person’s finger.The drop is put onto a special strip of paper, which is then inserted into theblood glucose monitor machine. The monitor measures and displays the bloodglucose reading. This test can monitor blood glucose fairly accurately if the personfollows the directions carefully.

What do the test results mean?

The normal blood glucose levels also vary depending on:

which test was performed

whether a person was fasting before the test

whether any special dietary or glucose substances were given during testing

Increased levels of blood glucose, a condition known ashyperglycemia, may be caused by the following:

acromegaly,a condition that causes elongation of the bones of the limbs and head

Cushing syndrome,a condition in which the level of the hormone cortisol is too high and causesfatigue, weakness,protein loss, swelling, and diabetes mellitus, which is also called DM

diabetes mellitus

diuretics, also known as water pills

gestational diabetes,or diabetes that develops during pregnancy

inadequate therapy for diabetes mellitus

infection in the pancreas, known as pancreatitis

kidney failure, such as chronic renal failure

liver disease,such as cirrhosis

pheochromocytoma,which is a noncancerous tumor that causes an increase in certain chemicalsthat can cause high blood pressure

steroid medicines, such as prednisone

stressresponse, including infection, severe burns,or surgery

Decreased levels of blood glucose, a condition known ashypoglycemia,may be caused by the following:

Addison disease,a condition in which there is a decreased amount of the adrenocorticol hormone

blood loss

extensive liver disease

hypopituitarism, a condition in which the pituitary gland does not release enough hormone

hypothyroidism,a condition in which too little thyroid hormone is present in the blood

insulin overdose

insulinoma, which is a tumor in the pancreas that causes too much insulin to be produced

malabsorption,or inadequate absorption of nutrients from the stomach or intestines

starvation