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Epic Test Code LAB164 Glucose 3 Hour Tolerance Test (Non-pregnant Adults and Pediatrics)

Performing Location(s)

BMC,CRH,LFH,HRK,OCH,FTT,FOX,FCC

Alternatives to OGTT

A challenge is not necessary if fasting blood sugar is >126 mg/dL on two occasions or a casual blood glucose > 200 mg/dL on two occasions as these are diagnostic for diabetes.

Specimen Type

Serum or Plasma

Preferred Container

Gold or Red top tube

Alternate Container

Green or Gray top tube

Blood Tube Draw Volume

Min 50% draw volume  

Minimum Volume to Submit for Testing

0.5 mL Serum or Plasma

  • Multiple test can be performed from this volume. For question please contact the lab at 547-3975.  

Transportation Needs

 Deliver specimen to laboratory within 1 hour of collection if unspun. If not possible see "storage Requirements". 

Storage Requirements

Sample tubes should be centrifuged within 2 hour of collection followed by transfer of the serum (red or gold top) or plasma (green top) to a labeled plastic, aliquot tube.

See Causes of Rejection for temperature requirements.
Gray top tubes do not require centrifugation for transport up to 48 hrs.

Causes for Rejection

Mislabeled or unlabeled specimen
Less than 50% draw for Vacutainer tubes
Patient not fasting prior to start of GTT
Stressed patient (surgery, infection, corticosteroids).
Specimen not labeled with hourly times.
>72 hours Refrigerated
> 8 hours Room Temperature
>5 days Frozen
Hemolysis > 500 mg/dL HgB
Lipemia > 700 mg/dL Trig
Bilirubin > 40 mg/dL Bili

Limitations

The oral glucose tolerance test is used for the diagnosis of gestational diabetes mellitus. It has also been used for the diagnosis of types 1 and 2 diabetes mellitus, but is not the optimal test for that purpose
The American Diabetes Association (ADA) recommends the fasting plasma glucose determination rather than the OGTT for the diagnosis of type 1 and type 2 diabetes mellitus.
Glucose will decrease in samples left on the clot, and in tubes other than fluoride (gray top tube) prior to analysis
Failure to have patients on 3 day high carbohydrate diet may result in a falsely abnormal GTT
Capillary collected blood may differ from venous due to contamination from hemolysis or interstitial fluid.

Reference Values

Diagnosis criteria for 3 Hr GTT (3GTTL)
(100 gram dose) 
Two or more glucose concentrations must exceed the reference range

Specimen

Normal Reference Range (mg/dL)

High Critical Value

Low Critical Value

Fasting

70- 100

>450

<40

1 hour

105 - 160

>450

<40

2 hour

95 - 130

>450

<40

3 hour

70 - 110

>450

<40

Days of Analysis

All

Available STAT

Yes

Includes

Fasting blood glucose followed by glucose levels drawn at timed intervals after administration of a glucose load – Urine is no longer collected or examined as a part of the glucose tolerance test.

Additional Information

Patient Instructions for Fasting Laboratory Testing
OGTT is contraindicated in the presence of obvious diabetes mellitus
Emesis may be an indication to cancel the remainder of a GTT for that day

Methodology

Beckman AU/Dx Series

CPT Code

82951 (x3), 82952

Last Updated

18-Mar-22 KT