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Test Code 8155 Glucose Tolerance Test, 75 G/2 Hour, Pre-Diabetes-Z13.1 (Type 1/Type 2 Diabetes), Non-Gestational, Plasma

Performing Laboratory

Barnes-Jewish Hospital Laboratory


Enzymatic (Hexokinase)
Literature References:

Package insert: Glucose/HK, Roche Corporation, 1/2006.

Specimen Requirements

Note: This test is to be ordered for pre-diabetes or diabetes screening when the diagnosis code Z13.1 is used.


Patient Preparation:
An 8 to 14 hour fast after 3 days of adequate carbohydrate loading (>150 g/day) is required.


Collection Procedure:
 1. Glucometer pre meter check is not for diagnostic purposes per American Diabetes Association; Diabetes Care:19(Suppl):562-6.

2. This test is not indicated if fasting glucose is >125 mg/dL.


Obtain glucometer reading and proceed as follows:


If glucometer glucose is <150 mg/dL
1. Draw fasting venous specimen.
2. Give patient 75 g glucose tolerance beverage.
3. Draw venous specimen at 2-hours post consumption.


If glucometer glucose is >150 mg/dL
1. Do not give glucose tolerance beverage.
2. Draw a venous specimen. Send STAT to Barnes-Jewish Hospital Laboratory for #1857 Glucose, Fasting.


If STAT Glucose, Fasting is <140 mg/dL
1. Give patient 75 g glucose tolerance beverage.
2. Draw venous specimen at 2-hours post consumption.


If STAT Glucose, Fasting is >140 mg/dL
Contact physician before proceeding. 


Specimen Type: Plasma

Container/Tube: Grey top (potassium oxalate/sodium fluoride)

Specimen Volume: Full tube


Additional Information: Draw times are required.

Day(s) Test Set Up

Monday through Sunday
Turnaround Time:
STAT: 1 hour after receipt in laboratory
Routine: 2 to 4 hours after receipt in laboratory

Reference Values

Glucose Tolerance Testing Reference Interval:

Type 1/Type 2 Diabetes Non-Gestational Adults:



Impaired Glucose Tolerance Possible Diabetes
Fasting 70-99 mg/dL 100-125 mg/dL ≥126 mg/dL
2-Hour 70-139 mg/dL 140-199 mg/dL ≥200 mg/dL

Intermediate 2-hour value indicates impaired glucose tolerance, while intermediate fasting value indicates impaired fasting glucose.

Critical result (automatic call-back): ≤50 mg/dL or ≥450 mg/dL

Literature Reference:

Diabetes Care 2005;28:Supplement 1,S37-S42.

Test Classification and CPT Coding

82947TS-Glucose, quantitation

82950TS-Glucose, post glucose dose

Additional Information

For BJH Laboratory Use Only
Alternate Tube:

1 dark green-top (lithium heparin) tube

1 lavender-top (EDTA) tube

1 mint green-top (lithium heparin) tube

1 red-top tube
Analyte Stability:

See Analyte Stability Chart in Special Instructions.

Laboratory Processing Instructions:
Test performed in BJH Core Lab.  Processed by automated line for delivery to the Cobas 8000. Completed specimens are stored refrigerated for 5 days. 

Specimen Transport Temperature


Special Instructions

LOINC Code Information

Name LOINC Code
Glucose in blood 2339-0
Fasting Glucose 1558-6
Glucose- 2 hours post 75 g glucose PO 1518-0