Glucose Tolerance Test-2 HR
Label Mnemonic: GT20
Epic Lab Code: LAB169
Downtime Form: A-1a General Laboratory Requisition
Chemistry
6240 RCP
356-3527
Specimen(s):
Plasma
Collection Medium:
Gray top tube 6 mL (Na Fluoride)
Alternate Collection Media:
Call laboratory for additional acceptable specimen collection containers.
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:
The criteria proposed by the Fourth International Workshop-Conference on Gestational Diabetes Mellitus (GDM) defines GDM as present if two or more of the following plasma glucose values are met or exceeded:
    Fasting plasma glucose concentration > 95 mg/dL (5.3 mmol/L)
    One-hour plasma glucose concentration > 180 mg/dL (10 mmol/L)
    Two-hour plasma glucose concentration > 155 mg/dL (8.6 mmol/L)
    Three-hour plasma glucose concentration > 140 mg/dL (7.8 mmol/L)

American Diabetes Association (ADA) guidelines define a 2 hr plasma glucose concentration of 200 mg/dL or greater following a 75 gram oral glucose load as one of the criteria for diagnosing diabetes mellitus.

References: (1) Carpenter MW, Coustan DR. Criteria for screening tests for gestational diabetes. Am J Obstet Gynecol 1982; 144:768; (2) Diabetes Care 34(Suppl 1): S62-S69, 2011.
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. Two hour Glucose Tolerance Test should include the following specimens: Fasting glucose 1 hour post glucose 2 hour post glucose CPT code is 82947 x number of specimens CPT code = 82947 x number of glucose performed
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
CPT Code:
See comments