Overview of GCT
What is GCT?
In the Glucose Challenge Test (GCT) - Obstetrical, blood glucose level is measured one hour after the administration of 50 gms of glucose solution. It is done to screen for and diagnose gestational diabetes (diabetes developing during pregnancy).
Why is GCT done?
The Glucose Challenge Test is performed to:
- Screen for high blood sugar in presence of risk factors for diabetes in pregnancy
- Detect gestational diabetes
What does GCT Measure?
Glucose Challenge Test (GCT) - Obstetrical measures blood glucose level one hour after the administration of 50 gms of glucose solution.
Glucose is a simple sugar or monosaccharide which is the main source of energy for all the cells of the body, and the only energy source for the nervous system. Carbohydrates consumed in the diet are broken down in the body to their simplest form, glucose. It is absorbed by the intestines and transported by the blood to various organs. Glucose is subsequently utilized by cells of these organs to produce energy wherever necessary, and the excess is stored either as glycogen in the liver for short-term storage or in fat tissues as triglycerides for long-term storage. The uptake, utilization, and storage of glucose after it is absorbed in the intestines are facilitated by the hormone, insulin which is secreted by the pancreas. Insulin influences the transport of glucose to the organs requiring it, like the heart, brain, working muscles, etc. It also directs storage of excess glucose. The action of insulin reduces sugar levels in the blood.
After every meal, sugar levels increase in blood and insulin is secreted as a response to reduce sugar levels until it becomes normal. If glucose levels fall too low in blood, another pancreatic hormone called Glucagon is released. Glucagon directs the liver to convert stored glycogen into glucose and release it into the blood. The insulin and glucagon hormones create a feedback mechanism to keep blood glucose levels within the normal range. Imbalance in their activity can cause an excess or shortage of blood sugar.
The glucose challenge test measures the levels of glucose in the blood, one hour after the administration of a sugar solution (usually 50 gm glucose dissolved in about 300 ml water). This helps to determine whether the body is able to utilize or store glucose efficiently. Excess sugar in blood indicates it is not being utilized or stored. It is usually performed as a part of the panel of tests performed during pregnancy and can be performed at any time during pregnancy. It is also necessary to repeat the test at 24 to 28 weeks to detect gestational diabetes.
Preparation for GCT
- Overnight fasting is not required.
- Intake of glucose solution (50 gms of glucose dissolved in 300 ml of water) is required one hour before the blood sample collection.
Sample Type for GCT
Interpreting GCT results
Normal range: Less than 130 to 140 mg/dL (7.2 to 7.8 mmol/L)
A cut-off value of 140 mg/dL (7.8 mmol/L) identifies 80% of women with Gestational diabetes.
A cut-off value of 130 mg/dl (7.2 mmol/L) identifies 90% of women with Gestational diabetes.
Blood sugar levels higher than the normal range indicates increased blood sugar due to the inability of the body to process it.
GCT is a screening test for Gestational diabetes and continuously raised blood sugar levels in subsequent tests indicate a strong possibility of gestational diabetes. Further tests like 2-hour or 3-hour Glucose Tolerance Tests (GTT) are performed to diagnose Gestational diabetes.
Answers to Patient Concerns & Frequently Asked Questions (FAQs) about GCT
Frequently Asked Questions about Glucose Challenge Test