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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

Day(s) Test Set Up

Monday through Saturday

Test Classification and CPT Coding

82951-First 3 specimens

82952-Each additional specimen

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.