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Glucose Tolerance Tests

Glucose Tolerance Tests is a topic covered in the Davis's Lab & Diagnostic Tests.

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General

Synonym/Acronym:
Standard oral tolerance test, standard gestational screen, standard gestational tolerance test, GTT.

Common Use:
To evaluate blood glucose levels to assist in diagnosing diseases such as diabetes.

Specimen:
Plasma collected in a gray-top (sodium fluoride) tube. Serum collected in a gold-, red-, or red/gray-top tube or plasma collected in a green-top (heparin) tube is also acceptable, but plasma is recommended for diagnosis. It is important to use the same type of collection container throughout the entire test.

Normal Findings:
(Method: Spectrophotometry)

Standard Oral Glucose Tolerance (Up to 75-g Glucose Load)
Conventional UnitsSI Units (Conventional Units × 0.0555)
Fasting sampleLess than 100 mg/dLLess than 5.6 mmol/L
Prediabetes or impaired fasting sample100–125 mg/dL5.6–6.9 mmol/L
2-hr sampleLess than 200 mg/dLLess than 11.1 mmol/L
Prediabetes or impaired 2-hr sample140–199 mg/dL7.8–11 mmol/L
Plasma glucose values are reported to be 10% to 20% higher than serum values.
Tolerance Tests for Gestational Diabetes
One-Step Approach (75-g Glucose Load)Conventional and SI Units (SI = Conventional Units × 0.0555)
Fasting sampleLess than 93 mg/dL (SI: Less than 5.2 mmol/L)
 1-hr sampleLess than 181 mg/dL (SI: Less than 10 mmol/L)
 2-hr sampleLess than 154 mg/dL (SI: Less than 8.5 mmol/L)
A diagnosis of gestational diabetes is made when any of the three thresholds are met or exceeded.Plasma glucose values are reported to be 10% to 20% higher than serum values.
Tolerance Tests for Gestational Diabetes
Two-Step ApproachConventional and SI Units (SI = Conventional Units × 0.0555)
Step OneStandard Gestational Screen (50-g Glucose Load)
1-hr sample performed while the patient is not fastingLess than 141 mg/dL; if results exceed 140 mg/dL, the 100-g GTT should be performedLess than 7.8 mmol/L; if results exceed 7.7 mmol/L, the 75-g GTT should be performed
Step TwoGestational GTT (100-g Glucose Load)Carpenter and CoustanNational Diabetes Data Group
Fasting sampleLess than 95 mg/dL (SI: Less than 5.3 mmol/L)Less than 105 mg/dL (SI: Less than 5.8 mmol/L)
 1-hr sampleLess 180 mg/dL (SI: Less than 10 mmol/L)Less than 190 mg/dL (SI: Less than 10.5 mmol/L)
 2-hr sampleLess than 155 mg/dL (SI: Less than 8.6 mmol/L)Less than 165 mg/dL (SI: Less than 9.2 mmol/L)
 3-hr sampleLess than 140 mg/dL (SI: Less than 7.8 mmol/L)Less than 145 mg/dL (SI: Less than 8 mmol/L)
A diagnosis of gestational diabetes is made when two or more of the four thresholds are met or exceeded.Plasma glucose values are reported to be 10% to 20% higher than serum values.GTT = glucose tolerance test.

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Citation

Bladh, Mickey Lynn., and Anne M. Van Leeuwen. "Glucose Tolerance Tests." Davis's Lab & Diagnostic Tests, 7th ed., F.A. Davis Company, 2017. Nursing Central, nursing.unboundmedicine.com/nursingcentral/view/Davis-Lab-and-Diagnostic-Tests/425150/all/Glucose_Tolerance_Tests.
Bladh ML, Van Leeuwen AM. Glucose Tolerance Tests. Davis's Lab & Diagnostic Tests. 7th ed. F.A. Davis Company; 2017. https://nursing.unboundmedicine.com/nursingcentral/view/Davis-Lab-and-Diagnostic-Tests/425150/all/Glucose_Tolerance_Tests. Accessed April 19, 2019.
Bladh, M. L., & Van Leeuwen, A. M. (2017). Glucose Tolerance Tests. In Davis's Lab & Diagnostic Tests. Available from https://nursing.unboundmedicine.com/nursingcentral/view/Davis-Lab-and-Diagnostic-Tests/425150/all/Glucose_Tolerance_Tests
Bladh ML, Van Leeuwen AM. Glucose Tolerance Tests [Internet]. In: Davis's Lab & Diagnostic Tests. F.A. Davis Company; 2017. [cited 2019 April 19]. Available from: https://nursing.unboundmedicine.com/nursingcentral/view/Davis-Lab-and-Diagnostic-Tests/425150/all/Glucose_Tolerance_Tests.
* Article titles in AMA citation format should be in sentence-case
TY - ELEC T1 - Glucose Tolerance Tests ID - 425150 A1 - Bladh,Mickey Lynn, AU - Van Leeuwen,Anne M, BT - Davis's Laboratory & Diagnostic Tests UR - https://nursing.unboundmedicine.com/nursingcentral/view/Davis-Lab-and-Diagnostic-Tests/425150/all/Glucose_Tolerance_Tests PB - F.A. Davis Company ET - 7 DB - Nursing Central DP - Unbound Medicine ER -