Glucose Tolerance Test-2 HR

Label Mnemonic:	GT20
Epic code:	LAB169
Order form:	Laboratory Requisition
Supply order:	Supply Order Form
Billing:	Billing Policies
CPT code:	82951 for the first 3 specimens and 82952 for each additional specimens

Specimen(s):

Plasma

Collection Medium:

	or
Gray top tube 6 mL (Na Fluoride)	or	Plasma Separator Tube 4.5 mL (Centrifuge Immediately)

Minimum:

3 mL; gray (sodium fluoride) top (or ONE microtube for pediatric patients) per specimen.

Testing Schedule:

24 hrs/day, 7 days a week, including holidays.

Turn Around Time:

1 hour (upon receipt in laboratory)

Reference Range:

If testing is intended for evaluation of gestational diabetes, consider use of the GTT 2 Hour (100 gram dose for pregnancy) [LAB8762] test.

General {Non-pregnant/Non-Postpartum}: < 155 mg/dL

Reference range for non-pregnancy glucose tolerance test using 75 g glucose.

Two-hour plasma glucose concentration:
< 140 mg/dL: normal
140-199 mg/dL: impaired glucose tolerance
200 mg/dL or higher: diabetes

Reference: Classification and Diagnosis of Diabetes: Standards of Medical Care in Diabetes—2020. American Diabetes Association. Diabetes Care 2020 Jan; 43(Supplement 1): S14-S31.

Comments:

Collect all specimens in gray top tube on patient care area and hold (sodium fluoride anticoagulant). Deliver all specimens simultaneously. Microtube specimens must be scheduled with the lab in advance and delivered immediately after drawing.

Test Limitations:

Icterus: No significant interference up to an I index of 60 
(approximate conjugated and unconjugated bilirubin concentration: 
60 mg/dL).

Hemolysis: No significant interference up to an H index of 1000 
(approximate hemoglobin concentration 1000 mg/dL).

Lipemia (Intralipid): No significant interference up to an L index of 
1000 (approximate triglycerides concentration 2000 mg/dL). There is 
poor correlation between turbidity and triglycerides 
concentration.

Methodology:

Hexokinase/UV Test

Instructions:

Gray top (Na Fluoride) collections: Transport whole blood to the laboratory within 24 hours.

Sample Processing:

Centrifuge within one hour of draw time.
Centrifuge at a speed and time necessary to get barrier separation of plasma/serum and cells.
Separate plasma or serum into labeled container and cap.

Sample Storage:

Refrigerate.

Transport Instructions:

Place labeled specimen into zip-lock type biohazard bag; seal bag.
Place completed requisition into outside pocket of bag.
Transport in cooler with refrigerated coolant packs.

CPT Code:

82951 for the first 3 specimens and 82952 for each additional specimens

See also:
GTT 2 Hour (100 gram dose for pregnancy), Plasma

See Additional Information:
Fasting Specimen Requirements