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Test Code LAB4099 GTT, 3 HOUR

Specimen Type

Preferred Specimen: Lithium Heparin Plasma (Mint Green Top, Dark Green Top)
Alternative Specimen: Serum (SST, Gold, Corvac, Tiger, Red Top Tube) Sodium Flouride (Gray Top Tube)

Collection Instructions

Draw fasting specimen just prior to 100 gram glucose load. Draw second sample 1 hour post dose, the third sample 2 hours after the dose and the fourth sample 3 hours after the dose. Clearly label specimens

Specimen Volume

2 mL each specimen

Minimum Volume

0.3 mL each specimen

Turnaround Time

STAT: 1 hour after receiving all specimens
Routine: 4 hours

Test Schedule

Daily

Sample Stability

3 days if separated from the cells within 30 minutes of collection

Method

Hexokinase

Reference Ranges

Gestational Diabetes Mellitus (GDM) screening:

  • Fasting < 95 mg/dL
  • 1 hour < 180 mg/dL
  • 2 hour < 155 mg/dL
  • 3 hour < 140 mg/dL

The diagnosis of Gestational Diabetes Mellitus (GDM) is met if 2 or more of the following criteria are met or exceeded.

These threshold values apply to blood glucose levels (measured fasted 1,2, and 3 hours) after 100 gram oral glucose load. These criteria apply to women at 24-28 weeks of gestation not previously diagnosed with diabetes. 

 

A 3 hour tolerance is no longer recommended for the diagnosis of Type 2 Diabetes.

Synonyms

GLUCOSE TOLERANCE, 3 HR (4 SPECIMENS)

CPT Codes

82950

Patient Prep

This test should be done in the morning after an overnight fast of between 8 and 14 hours, and after at least 3 days of unrestricted diet (150 or more grams carbohydrate per day) and unlimited physical activity. The patient should remain seated and should not smoke throughout the test. Patient can have nothing by mouth except water during test period. GLUCOSE DOSE: 100 grams