Glucose tolerance test
The glucose tolerance test (GTT) is a medical examination that assesses the body's ability to metabolize glucose, a key energy source. It is primarily utilized to diagnose conditions such as pre-diabetes, diabetes, and gestational diabetes, the latter occurring during pregnancy. The most common form, the oral glucose tolerance test (OGTT), involves the patient fasting, consuming a glucose solution, and then having blood samples taken at intervals to measure glucose levels. In contrast, the intravenous glucose tolerance test (IGTT) checks insulin levels after glucose is administered through an injection, helping predict potential diabetes development.
During pregnancy, screening for gestational diabetes is vital, as this condition can impact both maternal and fetal health. The testing process varies slightly for pregnant women, often requiring them to fast for a short period before longer tests if initial results indicate a risk. While glucose tolerance tests are generally safe, some patients may experience minor side effects like lightheadedness or bruising at the blood draw site. Normal glucose levels can vary based on the test type, and elevated results may necessitate further testing and specialist referrals for appropriate management.
Glucose tolerance test
A glucose tolerance test is a medical laboratory test that is done to measure the body's ability to use glucose, a simple sugar the body uses for energy. This type of test can be used to diagnose pre-diabetes and diabetes. Another form of the test is also used to diagnose gestational diabetes, which is diabetes that occurs during pregnancy. Glucose tolerance tests are important because they identify different types of diabetes, which is a complex group of diseases that causes people to have high blood sugar. Over time, high blood sugar can harm blood vessels and nerves. Untreated or undertreated diabetes can be extremely dangerous and have many negative effects on the body. Although different forms of glucose tolerance tests exist, the way in which they are administered is the same: the patient consumes glucose and a medical professional tracks how the patient's body metabolizes it.
Oral Glucose Tolerance Test (OGTT) and IV Glucose Tolerance Test (IGTT)
The most common type of glucose tolerance test is the oral glucose tolerance test (OGTT). At the beginning of the test, the patient has a blood sample drawn and then drinks a liquid containing a particular amount of glucose. The patient has a second blood sample drawn thirty minutes, an hour, or later to determine how his or her body is using the glucose. The test can take up to three hours. The OGTT is used most often to diagnose diabetes. Glucose is the sugar the body uses for energy, and people with diabetes often have high blood glucose levels. The test lets a doctor know if a patient's body is using glucose normally.
The IV glucose tolerance test (IGTT) is similar to the OGTT but is used to predict whether a patient will develop diabetes at a later time. Before the test begins, the patient has his or her insulin levels checked. During the IGTT, a patient receives an injection containing glucose. Then, one to three minutes after the injection is given, the patient's insulin levels are checked again.
Patients preparing for an OGTT or IGTT should eat and drink normally in the days before the test. Then, they will likely have to fast for eight hours before the test begins. Patients cannot eat or drink anything (expect some water) while the test is taking place. Patients taking either test should ask their doctor if any of their medications will interfere with the test.
Glucose Tolerance Test During Pregnancy
During pregnancy, women can develop a type of diabetes called gestational diabetes. While gestational diabetes occurs only when a woman is pregnant, it is like other types of diabetes in that it affects how the body uses glucose. This disease can raise the mother's blood sugar and also affect the blood sugar of the unborn fetus. An obstetrician can help a pregnant woman control gestational diabetes. The disease sometimes has no symptoms so doctors recommend that nearly all pregnant women be tested.
A glucose tolerance test for gestational diabetes is very similar to the OGTT. A pregnant woman first has a blood sample taken. Then she consumes a drink with glucose. Then she will have one more blood sample drawn to see how her body uses the glucose. Generally, the first test women take during pregnancy lasts for an hour. If the results from that test indicate the woman might have gestational diabetes, she will likely have to take a longer version of the same test.
When taking the glucose tolerance test during pregnancy, a patient should eat and drink normally for three days before the test. Generally, she does not have to fast or take any other precautions before the test; however, patients should follow any instructions their medical providers give them for the test. If a woman's results require her to take the longer version of the test, she may have to fast for eight to fourteen hours before the long test. During that fasting time, she will most likely be instructed to drink only water.
Results and Effects of Glucose Tolerance Tests
Since all glucose tolerance tests require patients to intake glucose, patients will feel the effects of the glucose, which are similar to drinking another sugary drink, such as soda. Serious side-effects from glucose tests are very rare, but patients might experience a hematoma (a bruise) or lightheadedness or develop an infection here the blood sample was drawn during the test.
Glucose levels that are considered normal will vary for the different types of tests. However, if the doctor believes that glucose levels are too high, the test could indicate pre-diabetes, diabetes, or gestational diabetes. If the doctor suspects that a patient has diabetes, the doctor will most likely refer the patient to a specialist, such as an endocrinologist, a registered dietician, or other specialist.
Even if the test results show that a patient has higher-than-normal glucose levels, it does not necessarily mean the patient has diabetes or gestational diabetes. Often, the test will be performed again or the doctor will do more research or tests to verify the diagnosis. Patients with pre-diabetes, diabetes, or gestational diabetes will all require different types of care.
Bibliography
"Diabetes Health Center." WebMD. WebMD, LLC. 14 Nov. 2014. Web. 17 Nov. 2015. <http://www.webmd.com/diabetes/gestational-diabetes-guide/oral-glucose-tolerance-test>
"Diagnosis of Diabetes and Prediabetes." National Institute of Diabetes and Digestive and Kidney Diseases. The National Institute of Diabetes and Digestive and Kidney Disease. June 2014. Web. 17 Nov. 2015. <http://www.niddk.nih.gov/health-information/health-topics/Diabetes/diagnosis-diabetes-prediabetes/Pages/index.aspx>
"Glucose Tolerance Test." Healthline. Healthline Networks, Inc. Web. 17 Nov. 2015. <http://www.healthline.com/health/glucose-tolerance-test#Overview1>
Mayo Clinic Staff. "Tests and Procedures: Glucose Tolerance Test." Mayo Foundation for Medical Education and Research. Mayo Clinic. Web. 17 Nov. 2015. < http://www.mayoclinic.org/tests-procedures/glucose-tolerance-test/basics/definition/prc-20014814>
"Oral Glucose Tolerance Test During Pregnancy." Cleveland Clinic. Cleveland Clinic. Web. 17 Nov. 2015. <https://my.clevelandclinic.org/health/diagnostics/hic-oral-glucose-tolerance-test-during-pregnancy >