Medical Terminology: Glucose Tests

1. What are Glucose Tests?
There are two pancreatic endocrine hormones secreted by the islet cells in the pancreas. These are insulin and glucagon. Both are secreted based on blood glucose levels. When the blood glucose is elevated, the pancreas secretes insulin, which causes glucose to cross the cell membrane and allows it to be used for energy, resulting in a decrease in blood glucose.
When blood glucose levels are low, the pancreas secretes glucagon, which signals the liver to release stored glucose into the blood, resulting in an increase in blood glucose. Other cells such as muscles also release glucose in response to glucagon.
Blood glucose must be maintained within a narrow range, which occurs naturally with the secretion of insulin and glucagon. However, failure of islet cells to properly function due to diseases such as diabetes, can result in high levels of blood glucose (hyperglycemia) or low levels of blood glucose (hypoglycemia).
Health care providers order glucose tests to monitor the blood glucose level. Based on the results of these tests, the health care provider may administer insulin or glucose to the patient.

2. C-Peptide Test
The C-peptide test to is used to differentiate between type 1. and type 2. diabetes and is used to assess the underlying cause of hypoglycemia and the result of removing an insulinoma (tumor) from the pancreas.

Understanding the C-Peptide Test
Proinsulin is the precursor to insulin produced by the beta cells of the islets of Langerhans in the pancreas. Proinsulin is split into C-peptide and insulin. The level of C-peptide is considered equal to the amount of insulin, indicating the amount of insulin made by the pancreas. The C-peptide test measures the level of C-peptide in blood and is used to differentiate between type 1. and type 2. diabetes.
The health care provider will order a blood glucose test along with the C-peptide test. The health care provider may order a C-peptide stimulation test to differentiate between type 1. and type 2. diabetes.

3. D-Xylose Absorption Test
The D-xylose absorption test is used to screen for malabsorption syndrome.

Understanding the D-Xylose Absorption Test
D-xylose is a simple sugar that is absorbed by the intestine. The D-xylose absorption test measures the level of D-xylose in blood.
D-xylose absorption can also be tested with a urine sample; however, a urine test is less accurate than the blood D-xylose absorption test for patients <12. years of age. The health care provider may order an upper gastrointestinal series if the D-xylose test is positive.

4. Blood Glucose Test
Blood glucose tests are used to screen for diabetes and hypoglycemia and assess treatment for diabetes.

Understanding Blood Glucose Tests
Glucose is the source of energy for cells and is transported into cells by insulin. As blood glucose levels rise following ingestion of food, the pancreas releases insulin to move the glucose from blood into cells. Blood glucose tests measure the level of glucose in the blood. There are four blood glucose tests:
. Oral Glucose Tolerance Test (OGTT): This test measures the blood glucose levels at specific time intervals after the patient ingests a glucose drink. The OGTT is ordered to screen for gestational diabetes and confirm positive results of other blood glucose tests.
. 2-Hour Postprandial Blood Sugar: This test measures blood glucose levels 2. hours after the patient ingests food.
. Fasting Blood Sugar (FBS): This test measures blood glucose levels after the patient has fasted for 8. hours. The FBS test is the initial test for diabetes.
. Random Blood Sugar (RBS): This test measures blood glucose levels several times a day regardless of food intake.
Glucose levels can also be measured in urine; however, this is not used to diagnose or monitor glucose levels. The health care provider may order the glycohemoglobin (GHb) blood test, which is used to monitor blood glucose levels for the previous 120. days.

5. Glycohemoglobin (GHb) Test
The glycohemoglobin (GHb) test is used to assess the treatment for diabetes and assess if the patient is adhering to the treatment plan.

Understanding the Glycohemoglobin Test
Glucose binds to hemoglobin in red blood cells, which has a life span of 120. days. The glycohemoglobin (GHb) test, commonly known as HgbA1c, measures the level of glucose bound to hemoglobin. This differs from the blood glucose test that measures the level of glucose in plasma. The health care provider orders the GHb test to assess if treatment is controlling diabetes and the patient is adhering to the treatment over a 120-day period.
The GHb test can be administered at any time; however, the health care provider is likely to order the test four times a year. The GHb test is not a replacement for the blood glucose test and cannot dictate hypoglycemia.

Basic Questions
Glucose Tests

1. Where is glucagon produced?
Glucagon is produced by the islet cells in the pancreas.

2. How do insulin and glucagon affect the blood glucose level?
When blood glucose is elevated, the pancreas secretes insulin, which causes glucose to cross the cell membrane and allows it to be used for energy, resulting in a decrease in blood glucose.
When blood glucose levels are low, the pancreas secretes glucagon, which signals the liver to release stored glucose into the blood, resulting in an increase in blood glucose.

3. What happens if the islet cells fail to properly function?
Failure of islet cells to properly function because of diseases such as diabetes can result in high levels of blood glucose (hyperglycemia) or low levels of blood glucose (hypoglycemia).

4. What is a cause of hypoglycemia?
Too much insulin is a cause of hypoglycemia.

5. What is the function of an insulinoma?
An insulinoma is a tumor that produces insulin.

6. What is the purpose of the C-peptide test?
The C-peptide test to is used to differentiate between type 1. and type 2. diabetes, and is used to assess the underlying cause of hypoglycemia, as well as the result of removing an insulinoma (tumor) from the pancreas.

7. How does the C-peptide test differentiate between type 1. and type 2. diabetes?
Proinsulin is the precursor to insulin produced by the beta cells of the islets of Langerhans in the pancreas. Proinsulin is split into C-peptide and insulin. The level of C-peptide is considered equal to the amount of insulin, indicating the amount of insulin made by the pancreas.

8. What is D-xylose?
D-xylose is a simple sugar that is absorbed by the intestine.

9. What is the purpose of the D-xylose absorption test?
The D-xylose absorption test is used to screen for malabsorption syndrome.

10. What might you expect the health care provider to order if the D-xylose absorption test is positive?
The health care provider may order an upper gastrointestinal series if the D-xylose test is positive.

11. Why would a health care provider not order a D-xylose urine test for a patient who is 10. years old?
D-xylose absorption can also be tested with a urine sample. Urine test is less accurate than the blood D-xylose absorption test for patients <12. years of age.

12. What might the health care provider order along with the C-peptide test?
The health care provider might order a blood glucose test along with the C-peptide test.

13. What is the purpose of a blood glucose test?
The blood glucose test is used to screen for diabetes and hypoglycemia and assess treatment for diabetes.

14. What is a common reason there is an increase in insulin production?
Ingestion of food is a common reason for an increase in insulin production.

15. What is the oral glucose tolerance (OGTT) test?
The OGTT measures the blood glucose levels at specific time intervals after the patient ingests a glucose drink. The OGTT test is ordered to screen for gestational diabetes and confirm positive results of other blood glucose tests.

16. What is the 2-hour postprandial blood sugar test?
The 2-hour postprandial blood sugar test measures blood glucose levels 2. hours after the patient ingests food.

17. What is the fasting blood sugar (FBS) test?
The FBS test measures blood glucose levels after the patient has fasted for 8. hours. The FBS test is the initial test for diabetes.

18. What is the random blood sugar (RBS) test?
The RBS test measures blood glucose levels several times a day regardless of food intake.

19. Why would the health care provider not order glucose levels to be measured in urine?
Glucose levels can be measured in urine; however, this is not used to diagnose or monitor glucose levels.

20. What is the purpose of the glycohemoglobin (GHb) test?
The GHb test is used to assess the treatment for diabetes and assess if the patient is adhering to the treatment plan.

21. Where in the blood does glucose bind?
Glucose binds to hemoglobin in red blood cells (RBCs).

22. Why does the result of the GHb test represent the patient’s condition for the previous 120. days?
Red blood cells have a life span of 120. days.

23. How does the GHb test differ from the blood glucose test?
The GHb test measures glucose bound to hemoglobin in RBCs. The blood glucose test measures glucose in plasma.

24. When is the health care provider likely to order the GHb test?
The GHb test can be administered at any time; however, the health care provider is likely to order the test four times a year.

25. For what is the GHb test unable to screen?
The GHb test is unable to screen for hypoglycemia.