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Test Code GTTS Glucose Tolerance Testing

Additional Codes

Cerner

NextGen

Glucose Tolerance 1/2 Hour

Glucose Tolerance 1/2 Hour

Glucose Level 50 Gram

Glucose Level 50 Gram

Glucose Tolerance 2 Hour

Glucose Tolerance 2 Hour

Glucose Tolerance 3 Hour

Glucose Tolerance 3 Hour

Glucose Tolerance 3 Hour Pregnant

Glucose Tolerance 3 Hour Pregnant

Glucose Tolerance 4 Hour

Glucose Tolerance 4 Hour

Glucose Tolerance 5 Hour

Glucose Tolerance 5 Hour

Methodology

Colorimetric (reflectance spectrophotometry) using Glucose Oxidase.

Patient Preparation

Glucose Tolerance Testing Form

 

  • Glucose Level 50 Gram: One Hour 50 g Glucose Instructions
    • Fasting is not required unless requested by provider.
    • Fasting Glucose is measured and evaluated before proceeding (65-126 mg/dL is acceptable).
    • 50 g glucose beverage is consumed by patient within 5 minutes.
    • 1 hour post-consumption glucose is performed and evaluated before patient is released (60- 200 mg/dL is acceptable).
  • All other Tolerance Tests: Tests Requiring Fasting and Fasting Instructions
    • 8 hour fast is required.
    • Fasting Glucose is measured and evaluated before proceeding (65-126 mg/dL is acceptable).
    • 75 g glucose for non-pregnant adults and 100 g glucose for pregnant adults is consumed by patient within 5 minutes.
    • Glucose measurements are performed based on the ordered procedure.
    • The final measurement is evaluated before patient is released (60- 200 mg/dL is acceptable).

Collection Instructions

Standard phlebotomy practices.

Specimen Requirements

Container

Specimen Type

Tube

Lithium Heparin Plasma

PST

 or  or 

Serum

 or 

SST

 or  or 

 

Stability

Storage

Temperature

Stability

Room Temperature

18-28°C

≤ 24 Hours

 

Refrigerated

 2-8°C

≤ 7 days

 

Frozen

≤-18 °C

≤ 1 year

 

Rejection Criteria

Gross Hemolysis

Result Reporting and Reference Values

Reported in mg/dL.

Age

Low

High

Critical Low

Glucose Tolerance for Non-Pregnant 75 gram load:

Test note: 2 hour result reference based on ADA guidelines. Categories for increased risk for diabetes: a 2 hour result of 140-199 mg/dL is an increased risk of diabetes (prediabetes) or a 2 hour value ≥ 200 mg/dL with a confirmed result on a subsequent day is diagnostic for diabetes.

½ hour (Optional)

110

170

50

1 hour

120

170

50

1 ½ hour (Optional)

100

140

50

2 hour

70

139

50

3 hour

70

105

50

4 hour

70

105

50

5 hour

70

105

50

Glucose Tolerance 50 gram load for Gestational Diabetes:

 

Normal

Critical Low

1 hour

< 140

50

Glucose Tolerance for Gestational Diabetes 100g load (ADA Recommendation)

 

Normal

Critical Low

Fasting

< 99

50

1 hour

< 180

50

2 hour

< 155

50

3 hour

< 140

50

Reflex Testing

None

Limitations

  • Ortho reports a bias with the following:
    • Glutathione at 61.5 mg/dL has a -8.6 bias
  • Ortho reports no significant interference with the following:
    • Bilirubin at 40 mg/dL

Useful For

Glucose is a primary cellular energy source. Fasting plasma glucose concentrations and tolerance to a dose of glucose are used to establish the diagnosis of diabetes mellitus and disorders of carbohydrate metabolism. Glucose measurements are used to monitor therapy in diabetics and in patients with dehydration, coma, hypoglycemia, insulinoma, acidosis, and ketoacidosis.

A fasting specimen is analyzed before beginning the GTT. The testing beverage is administered based on the results of the fasting glucose level. In general, glucose levels should return to normal within 2 hours after ingesting of the glucose.