Glucose Tolerance, Gestational Screen 1 Hour


Sunquest Code:GLU1  
Epic Code:LAB3503Epic Name:Glucose Tolerance, Gest Screen1 Hour
Order Instructions:Order as GCT and add coded comment 5001 (One hour post 50 g glucose load).
Synonyms:Glu OB; Glucose 1; GTT; Glucose Challenge; GCT1; GLC; Gestational Glucose; GLU1
Methodology:Bichromatic end point, glucose oxidase
CPT Code:82950
Test Includes:Blood glucose level collected one hour after ingestion of 50 g glucose
Turnaround Time:Performed Mon-Fri, 0700-1700; turnaround time is 2 hours routine, 40 minutes stat.
Special Instructions:This is a screening test usually administered between 24-28 weeks of pregnancy.
Associated Links:

Glucose Tolerance Testing



Collection Instructions

Specimen:Blood
Optimal Volume:2.5 mL
Minimum\Peds Volume:0.6 mL
Container:Green (lithium heparin, gel) (Green (sodium heparin, no gel), Green (sodium heparin, no gel) on ICE, Gray (sodium fluoride + potassium oxalate), Red (no gel), Red or gold (gel))
Collection Instructions:Patient must plan to remain in laboratory lobby for one hour after oral 50 g glucose load. Administer 50 g glucose solution; patient should drink the solution completely in a timely manner. Collect blood specimen one hour after patient finishes the glucose solution. Patient must not eat, smoke, or ingest caffeinated drinks during the one hour period between ingestion of glucose solution and blood collection. Water is allowed. No caloric intake is required.
Patient Preparation:Patient does not need to be fasting and needs no preparation. The gestational diabetic screen is performed without regard to last meal or time of day.
Contraindications:If patient becomes ill or vomits, test must be discontinued.


Processing and Shipping

Specimen Processing:Centrifuge and aliquot 1.25 mL, 0.2 mL minimum. Store in refrigerator.
Shipping Instructions:Ship at refrigerated temperature.
Stability:Outpatient Laboratory will collect specimens in green top (heparin) or red/black top (gel) tubes to avoid hemolysis. Clinic should collect in gray top (NaF) tubes because specimens may not be delivered promptly. For Women's Health Clinic: 1) WHC will drop off request form to be filed in the future order file. 2) Patient will check into the lab to drink the 50g glucola (no blood is drawn pre-glucola for the 50g screen). 3) OP Lab will set the timer for 1 hour. 4) OP Lab will send a lab staff to WHC to draw the 1 hour post sample and other labs if needed. Stability: Once separated from cells, Room temperature - 8 hours; refrigerated - 72 hours.
Test Performed at or Referral Lab Chemistry  (University of Minnesota Health Maple Grove Clinics, Fairview Range - FRMC, UMMC-East Bank, Oxboro Bloom, Fairview Lakes - FLMC, Fairview Ridges - FRH, Fairview Northland - FNMC, Fairview Southdale - FSH, UMMC/UMMCH-West Bank)


Interpretive

Reference Range:

Reference value at 1 hour less than or equal to 130 mg/dL following 50 g glucose load. This is a screening test for gestational Diabetes Mellitus. If results are abnormal a Standard Gestational Glucose Tolerance test should be ordered.

 

Interpretation:

A fasting glucose greater than 126 mg/dL or a casual plasma glucose greater than 200 mg/dL meets the threshold for the diagnosis of diabetes if confirmed on a subsequent day and precludes the need for a glucose challenge. In the absence of this degree of hyperglycemia, evaluation for GDM in women at average or high risk should follow one of two approaches.

 

Two-Step Approach:

Perform initial screening with glucose challenge (GCT), a plasma/serum glucose 1 hour after 50 g oral glucose load. Perform a gestational oral glucose tolerance (OGTT) on the subset of women exceeding the glucose threshold value on the GCT. A glucose greater than or equal to 140 mg/dL on the GCT identifies approximately 80% of women with GDM, and the yield is further increased to 90% by using a cutoff of greater than or equal to 130 mg/dL.

 

One-Step Approach:

Perform gestational oral glucose tolerance test (OGTT) without prior screening.

 



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