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What is a Glucose Challenge test?

A glucose challenge test (GCT) is used to diagnose diabetes and prediabetes in a wide range of population, including the elderly and youngsters, overweight individuals and individuals with or without a family history of diabetes. It is also recommended for the diagnosis of gestational diabetes in pregnant women, which occurs only during pregnancy and affects both the mother and the baby. GCT determines how glucose is processed in body and a glucose tolerance test is needed to confirm the presence of diabetes in women with abnormal results on GCT.

GCT is considered a standard test to be performed during the early phase of the third trimester of pregnancy. It is generally recommended during the 24th to 28th week of pregnancy. Timely diagnosis and appropriate management of this condition can help prevent pregnancy complications.

  1. Why is Glucose Challenge test performed?
  2. How do you prepare for Glucose Challenge test?
  3. How is Glucose Challenge test performed?
  4. What do Glucose Challenge test results mean?
  5. How much does a Glucose Challenge test cost?

This test is recommended in pregnant mothers who are at risk for diabetes, such as those with:

It is also suggested to women who are physically inactive during pregnancy.

Most often, gestational diabetes does not exhibit any apparent signs or symptoms. Sometimes, the condition is too mild to produce any symptoms. However, pregnant mothers experiencing the following symptoms may be ordered to undergo this test:

No special preparations such as fasting or restriction of food or drinks are needed prior to this test. However, pregnant women are made to drink a sweet fluid and wait for an hour before the test is conducted.

Many factors may interfere with test result; thus, always consult a doctor to know if any special preparations are needed for this test and incorporate them in the duration before the test to obtain correct results.

The pregnant woman is required to drink a sweet liquid that contains glucose. A blood sample is withdrawn one hour after the consumption of the drink as blood glucose levels are known to peak at approximately an hour.

A blood sample is usually withdrawn from a vein in the arm using a needle. It can also be obtained by a finger prick. An elastic band called tourniquet may be tied around the arm, which causes it to swell, thus allowing the laboratory technician to locate the vein easily. 

Blood tests pose some risks such as bruising, bleeding, infection, and a feeling of lightheadedness. Slight pain may be experienced during the test when the needle is inserted into the vein. The site of injection may be sore for some time after the test. The woman may feel nauseated, and experience a headache or stomach ache due to the sweet liquid; however, these symptoms will get better after the test.

Normal results:

A blood glucose level of <140 mg/dL is considered to be normal.

Abnormal results:

A blood glucose level of >140 mg/dL is considered to be abnormal. Abnormally high levels of glucose in GCT may indicate that the body is unable to process glucose correctly.

  • Blood glucose levels in the range of 140-199 mg/dL in pregnant mothers indicate the presence of impaired glucose tolerance
  • Blood glucose levels of ≥200 mg/dL in pregnant mothers indicates diabetes

In the case of abnormal results, the pregnant woman is recommended to get a glucose tolerance test done. This is because not all women who have abnormal findings on GCT may have diabetes. Therefore, a glucose tolerance test helps in confirming the diagnosis.

Based on the results of GCT and glucose tolerance test, the doctor may recommend certain dietary and lifestyle changes along with appropriate therapeutic measures to maintain and improve the health of the mother and the baby.

Disclaimer: All results must be clinically correlated with the patient’s complaints to make a complete and accurate diagnosis. The above information is provided from a purely educational point of view and is in no way a substitute for medical advice by a qualified doctor.  

The cost of GCT may vary in different cities and laboratories; however, the average cost is anywhere between 100 and 200 INR.

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  1. Woodruf Health Sciences Center: Emory University; Glucose Challenge Test is Accurate and Economical for Diabetes and Prediabetes Screening
  2. National Institute of Diabetes and Digestive and Kidney Diseases [internet]: US Department of Health and Human Services; Gestational Diabetes
  3. American Pregnancy Association; Glucose Tolerance Test
  4. University of Rochester Medical Center [Internet]. Rochester (NY): University of Rochester Medical Center; Glucose Tolerance
  5. National Heart, Lung, and Blood Institute [Internet]. Bethesda (MD): U.S. Department of Health and Human Services; Blood Tests
  6. Katarzyna Madziarska et al. Glucose challenge test (50-g GCT) in detection of glucose metabolism disorders in peritoneal dialysis patients: preliminary study. Int Urol Nephrol. 2015; 47(4): 695–700. Published online 2014 Dec 25. doi: 10.1007/s11255-014-0900-1. PMID: 25539618
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