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Test Code LAB164 Glucose Tolerance, 3 Hour

Additional Codes

GTT 3 HR

Collection:

Specimen: Blood 

Preferred: Lt Green w/ Gel - Li Hep

Acceptable: Serum Separator, Plain Red or Gray Top Tube

Specimen Volume: 5 mL; Minimum 1.0 mL.Fill gray tube to draw line.

 

Pediatric Collection:

One Green, Gold or Plain Red microtainer filled to 600 uL.

.

Stability:

Blood specimens collected in a Gray Sodium Flouride tube are stable in whole blood state for:

 

Ambient: 24 Hours

Refrigerated (preferred): 72 Hours

 

Specimens collected in a Lithium Heparin Green, Gold Serum Separator or Plain Red should be separated from red cells ASAP to avoid loss of analyte concentration. Once serum/plasma is separated from cells:

 

Ambient: 8 Hours

Refrigerated (preferred): 1 Week

Frozen: 2 Weeks

Turn Around Time (TAT):

STAT: 1 HOUR

Routine: 4 HOURS

Test Availability:

24 hours a day / 7 days a week

Reference Interval:

No established reference range

Interpretive Data:

Interpretation of oral glucose tolerance test (OGTT):


1. Criteria for the diagnosis of diabetes:

 

Fasting plasma glucose (FPG) >125 mg/dL. Fasting is defined as no calorie intake for at least 8 h
                 OR
Casual plasma glucose (PG) >199 mg/dL with symptoms of diabetes including polyuria, polydipsia, and unexplained weight loss
                 OR
2-h plasma glucose >199 mg/dL during an OGTT with a 75-gm glucose load

 

Each category must be confirmed on a subsequent day unless unequivocal symptoms of hyperglycemia are present.

 

2. Hyperglycemia not sufficient to meet the diagnostic criteria for diabetes is characterized as either impaired fasting glucose (IFG) or impaired glucose tolerance (IGT)


     IFG = FPG 100 - 125 mg/dL
     IGT = 2-h PG 140-199 mg/dL

 

3.  Screening of gestational diabetes on the basis of 1-h OGTT (50-gm glucose load):

 

     1-h glucose >139 mg/dL, pursue 3-h OGTT (100-gm glucose load)

 

4. Criteria for the diagnosis of gestational diabetes on the basis of an OGTT (100-gm glucose load):

 

Two or more of the plasma glucose values must be met or exceeded
               (1) Fasting: 95 mg/dL
               (2) 1-h: 180 mg/dL
               (3) 2-h: 155 mg/dL
               (4) 3-h: 140 mg/dL

Performing Laboratory Section

Chemistry / UMC MAIN LABORATORY