The key difference between OGTT and HbA1c is that OGTT is a diagnostic test for diabetes that has a higher sensitivity and lower specificity, while HbA1c is a diagnostic test for diabetes that has a lower sensitivity and higher specificity.
Diabetes is a common condition that affects millions of people worldwide. In order to diagnose prediabetes, type 1 or type 2 diabetes, or gestational diabetes, individuals need to undergo specific tests to determine if their blood sugar levels are within normal ranges. There are different tests available in laboratories, such as OGTT, HbA1C test, fasting blood sugar test, random blood sugar test, glucose screening test, etc. OGTT and HbA1c are two different types of tests for diagnosing diabetes.
CONTENTS
1. Overview and Key Difference
2. What is OGTT
3. What is HbA1c
4. Similarities – OGTT and HbA1c
5. OGTT vs HbA1c in Tabular Form
6. Summary – OGTT and HbA1c
What is OGTT?
The glucose tolerance test (GTT) is a diagnostic medical test used to determine if someone has diabetes, whereby a glucose solution is administered, and blood samples are taken at specific intervals to measure the rate at which the body clears the glucose from the bloodstream. This test is used to detect diabetes, insulin resistance, impaired beta cell function, reactive hypoglycemia, acromegaly, and rarer disorders of carbohydrate metabolism. OGTT (oral glucose tolerance test) is the most commonly used version of the GTT. In this version, a standard dose of glucose is ingested by mouth, and the blood glucose levels are later (2 hours after) checked for glucose clearance. Moreover, many variants of the GTT were devised over the years for different purposes. The OGTT determines whether the human body has difficulty metabolizing the intake of sugar.
OGTT is useful for detecting prediabetes, gestational diabetes in pregnant women, insulin resistance, and reactive hypoglycemia. This test has a higher sensitivity and lower specificity. For people with diabetes, the typical results of an OGTT include a fasting blood glucose level before the test of over 7.0 mmol/L and a blood glucose level of over 11.0 mmol/L two hours after the test. Furthermore, for normal people, the test results would be fasting value (before the test): under 6 mmol/L and after 2 hours: under 7.8 mmol/L.
What is HbA1c?
HbA1c (glycated hemoglobin) is a form of hemoglobin (Hb) that is chemically linked to sugar. Glucose, galactose, and fructose spontaneously bond with hemoglobin when present in the bloodstream. However, glucose is less likely to do so than galactose and fructose. This is why glucose is used as the primary metabolic fuel in humans. Therefore, the formation of the sugar hemoglobin linkage (HbA1c) indicates the presence of excessive sugar in the blood or is indicative of diabetes.
A glycated hemoglobin test is recommended for checking and controlling blood sugar in prediabetic people and monitoring blood sugar control in patients with more elevated levels (diabetes mellitus). The hbA1c test is primarily used to determine a three-month average blood sugar level. Furthermore, the test result of >6.4% indicates the state of diabetes mellitus. In addition, the HbA1c test has lower sensitivity and higher specificity.
What are the Similarities Between OGTT and HbA1c?
- OGTT and HbA1c are two different types of tests for diagnosing diabetes.
- Both tests can be used to detect prediabetic and diabetic people.
- These tests are routinely available in common laboratories.
- They are inexpensive tests for diagnosing diabetes.
What is the Difference Between OGTT and HbA1c?
OGTT is a diagnostic test for diabetes that has higher sensitivity and lower specificity, while HbA1c is a diagnostic test for diabetes that has lower sensitivity and higher specificity. Thus, this is the key difference between OGTT and HbA1c. Furthermore, OGTT is performed after fasting for 8 to 12 hours, but fasting is not needed to perform HbA1c.
The below infographic presents the differences between OGTT and HbA1c in tabular form for side-by-side comparison.
Summary – OGTT vs HbA1c
Diabetes is a chronic disease that occurs when the pancreas does not produce enough insulin or when the body cannot use the insulin effectively that it normally produces. OGTT and HbA1c are two different types of tests for diagnosing diabetes. OGTT test has higher sensitivity and lower specificity, while HbA1c test has lower sensitivity and higher specificity. So, this summarizes the difference between OGTT and HbA1c.
Reference:
1. “Oral Glucose Tolerance Testing.” Australian Family Physician, The Royal Australian College of General Practitioners.
2. “Hemoglobin A1C (hba1c) Test.” MedlinePlus, U.S. National Library of Medicine.
Image Courtesy:
1. “Diabetes” By (CC0) via Pixabay
2. “2019.05.13 Inadvertent Glucose Tolerance Test, Washington, DC USA 9673” By Ted Eytan (CC BY-SA 2.0) via Flickr