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Test Code GTT4HR Glucose Tolerance, 4 hours, LAB165

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.

                                         Additional specimens will be drawn at 1/2 hour, 1 hour, 2 hours, 3 hours,

                                         and 4 hours post dose.

Note: Label specimen appropriately (plasma and fasting, 1/2 hour, 1 hour, 2 hours, 3 hours, or 4 hours post dose).



Reference Values

Fasting: <100 mg/dL

1/2 Hour: <200 mg/dL

1 Hour: <200 mg/dL

2 Hour: <140 mg/dL

3 Hour: <130 mg/dL

4 Hour: <110 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

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.

Day(s) Test Set Up

Monday through Saturday



Test Classification and CPT Coding

82951-First 3 specimens

82952-Each additional specimen