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Test Code GTT2H Glucose Tolerance, 2 hours, LAB169



Performing Laboratory

St. Luke's Hospital Cedar Rapids

Specimen Requirements


Preferred: Green-top (lithium heparin) tube

Acceptable: Gold-top serum gel tube or plain red-top tube

Specimen Volume: 0.1 mL of plasma or serum

Stability: Separated specimens are stable for as long as 8 hours at 25°C and up to 72 hours at 4°C.

Collection Instructions: A fasting specimen will be drawn, then a 75 g glucose load given.

                                         A second specimen will be drawn 2 hours after glucose load is given.

Note: Label specimen appropriately ( fasting and 2 hours post dose).



Reference Values


Fasting: <100 mg/dL

2 Hour: <140 mg/dL


Fasting: 100-126 mg/dL

2 Hour: 140-200 mg/dL


Fasting: >126 mg/dL

2 Hour: >200 mg/dL


Critical Lows

0-2 days:  <46 mg/dL

>2 days:  <70 mg/dL

Critical Highs

0-7 days: >200 mg/dL

>1 week: >400 mg/dL

Day(s) Test Set Up

Monday through Saturday

Test Classification and CPT Coding


82950-Post glucose

Useful For

Glucose Tolerance tests have traditionally been used for the diagnosis of reactive hypoglycemia. “Reactive” hypoglycemia is hypoglycemia that occurs following a meal and is classified as alimentary, functional, or that found in diabetics or people with impaired glucose tolerance.