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Test Code LAB169 Glucose, Standard Tolerance Test, 75 g Glucose Load, Plasma or Serum

Important Note

NOTE: Glucola must be consumed within 10 minutes.

NOTE: Specimen cannot be collected prior to the time due and no more than 10 minutes past the time due.

Reporting Title

Standard OGTT “75g”

Methodology

Roche Diagnostics, Hexokinase

According to 2004 American Diabetic Association guidelines:  Either oral glucose tolerance test (OGTT) or fasting plasma glucose (FPG) may be used to diagnose diabetes, however, FPG is greatly preferred due to ease of administration, convenience, acceptability, and lower cost.

Performing Laboratory

OhioHealth Laboratory Services - RMH, BH, DH, DMH, GMC, GMH, HMH, MGH, MH, OBH, SH Core Laboratories

Specimen Requirements

Patient Preparation

1. Patient should fast overnight (8-14 hours).

2. Patient should have had at least 3 days of unrestricted diet (with >150 g of carbohydrate per day) and unlimited physical activity. Patients on low carbohydrate diets must maintain 150 g carbohydrate diet for 3 days for valid results.

3. Patient should remain seated, with nothing to eat, drink, or chew during test except for water if desired. Patient may not smoke.

4. It is best if patient does not take medication during test or 3 days prior. Salicylates, diuretics, and anticonvulsants decrease insulin secretion.

 

Performance of Test

1. Draw a fasting specimen. Label specimen with time of draw and as “fasting.”

2. Administer a 75 g dose of GlucolaTM which should be consumed as quickly as possible. Note time that patient finishes GlucolaTM. To determine correct amount of GlucolaTM, refer to side of bottle. There are 10 g of glucose per ounce, therefore, give patient 7.5 oz.

4. If patient vomits, test must be rescheduled.

5. Draw specimen 2 hours after GlucolaTM was finished. Label specimen with time of draw and as “2 hour.”

 

Specimen Collection

Submit only 1 of the following specimens:

 

Preferred:

Draw blood in a  grey-top (potassium oxalate/sodium fluoride) tube. Send whole blood
Note:  1.  Label specimens appropriately to indicate specimen timing.

 

Alternate:

Serum or plasma

Draw blood in a plain, red-top; gold-top; or speckled-top serum gel tube(s) or a green mint top (Heparin) gel tube.  Spin down and send 1 mL of serum or plasma refrigerated. It is important to separate cells from serum as soon as possible..

Note:  1. Indicate serum or plasma on the specimen.
            2. Label specimen appropriately to indicate collection timing.

 

Specimen Stability Information

 

Specimen Type Temperature Time
Serum or plasma Refrigerated 72 hours
  Ambient  8 hours
  Frozen  3 days

 

SODIUM FLORIDE TUBE STABLE FOR 3 DAYS AT ROOM TEMPERATURE

 

Specimen Transport Temperature

Refrigerate: OK

Ambient: OK

Frozen: OK

Reference Values

Fasting:  65-99 mg/dL

 

2 hour:  65-139 mg/dL

 

American Diabetic Association 2005 guidelines for diagnosis of diabetes mellitus:  A diagnosis of diabetes must be confirmed by retesting on a subsequent day unless unequivocal symptoms of hyperglycemia are present. Retest may be by FPG (indicative of diabetes mellitus [DM] at ≥126 mg/dL) or by OGTT, or by random plasma glucose if symptoms are present (indicative of DM at ≥200 mg/dL).

Test

Normal

(mg/dL)

IFG*

or IGT**

(mg/dL)

Diabetes

(mg/dL)
       

FPG

65-99

100-125

≥126

2-Hour Post 75 g Glucose Load (OGTT)

65-139

140-199

≥200
     

Symptoms of DM and random plasma glucose ≥200

*Impaired Fasting Glucose

**Impaired Glucose Tolerance

 

Critical values: <56 mg/dL or >400 mg/dL

Alerting category:  Always called within 1 hour 

Day(s) Test Set Up

Monday through Sunday

Test Classification and CPT Coding

82947 - fasting glucose

82950 - post-GlucolaTM dose (includes GlucolaTM)