1 hour Oral Glucose Tolerance Test, OGTT, GTT , one hour oral glucose challenge test, GCT (serum, plasma)
| Units | Fasting | 1 hour | ||
| mg/dL | Not required | 130 or 140 | ||
| mmol/L | Not required | 7.2 or 7.8 |
The one hour oral glucose challenge test [GCT] is a screening test for gestational diabetes that measures plasma or serum glucose concentration 1 hour after a 50-g oral glucose load. A blood sugar value >140 mg/dl (7.8 mmol/l) identifies approximately 80% of women with gestational diabetes (GDM), a cutoff of >130 mg/dl (7.2 mmol/l) identifies 90% of women with GDM.The California Diabetes and Pregnancy Program recommends that women with values 140 mg/dl to 179 mg/dl should have a 3-hour 100 gram oral glucose tolerance test (OGTT) within one week. If the patient has a screening value > 180 mg/dl, a fasting blood sugar should be checked as soon as possible. If the fasting is > 95 and the one hour screening test > 180 mg/dl this provides two abnormal values and the 3 hour OGTT is not required. If the fasting value is less than 95 then proceed with the 3 hour OGTT.
A glucose challenge test is not necessary in patients with a fasting plasma glucose level >126 mg/dl (7.0 mmol/l) or a casual plasma glucose >200 mg/dl (11.1 mmol/l) since these values meet the threshold for the diagnosis of diabetes.
References:
1. Guidelines for Care, California Diabetes and Pregnancy Program,2002
2. American Diabetes Association.Diagnosis and classification of diabetes mellitus. Diabetes Care. 2009 Jan;32 Suppl 1:S62-7. PMID:19118289
Important Note
This is a non-fasting test.
This test is recommended and only available as a screen for PREGNANT patients at 24-28 weeks gestation. The patient is given a 50 gram oral glucose load and blood is drawn one hour later.
For outpatient collection: Providers please instruct patient to arrive at least 90 minutes prior to the lab closing to ensure there is enough time to complete the test. LINK: List of Laboratory Locations and Hours
Test Name Alias
Glucose 1 hr Post 50 g | Glucose Tolerance | Glucose | GTT | OGTT | 8040
Interface Order Alias
10146
Ordering Instructions
This test is recommended and only available as a screen for PREGNANT PATIENTS at 24-28 weeks gestation.
For safety and accuracy of testing, patients are encouraged to have Oral Glucose Tolerance Tests (OGTT) performed at one of our Outpatient Service Centers.
GlucoCrushTM, the glucola drink used in Spectrum Health Grand Rapids Laboratory does not contain gluten.
Specimen Requirements
Specimen Collection: Blood
Container(s): 4.5 mL Mint Green Top (Lithium Heparin Gel) or 5.0 mL Gold Top (Serum Separator-SST Gel)
Preferred Volume to Collect: 4.5 mL
Minimum Volume to Collect: 1.0 mL
Capillary collect ok? Yes
Microtainer acceptable: Yes
Collection Instructions:
- Avoid hemolysis
- After collection, gently invert tube 8-10 times.
- Specimen should be processed within 2 hours – See Processing Instructions.
Processing Instructions (Laboratory, Outpatient or Off-site collection)
- Processed Specimen: Plasma or Serum
- Centrifuge/Spin: Yes
- Aliquot: Yes
- Processes Minimum Volume: 0.5 mL Plasma or Serum
- Processing Instructions:
- Plasma is preferred specimen type
- Green Tube/Plasma: Centrifuge within 1 hour after collection.
- Gold Tube/Serum: Allow blood to clot for 30 minutes in a vertical position and centrifuge within 2 hours.
- Minimum plasma/serum volume: 0.5 mL
- Transport Temperature: Refrigerated
GlucoCrushTM, the glucola drink used in Spectrum Health Grand Rapids Laboratory does not contain gluten.
Specimen Stability
Ambient: 8 hours
Refrigerate: 72 hours
Frozen: aliquot plasma/serum for longer storage
Laboratory Retention: 72 hours
Test Frequency
Available daily, usual TAT 1 day.
Reference Range
Female
65 – 135 mg/dL
Performing Department
CHEMISTRY
Performing Department Laboratory Location
Spectrum Health Regional Laboratory, Grand Rapids, MI
Spectrum Health Big Rapids Laboratory, Big Rapids, MI
Spectrum Health Blodgett Laboratory, Grand Rapids, MI
Spectrum Health Gerber Laboratory, Fremont, MI
Spectrum Health Kelsey Laboratory, Lakeview, MI
Spectrum Health Ludington Laboratory, Ludington,
MI
Spectrum Health Pennock Laboratory, Hastings, MI
Spectrum Health Reed City Laboratory, Reed City, MI
Spectrum Health United Laboratory, Greenville, MI
Spectrum Health Zeeland Laboratory, Zeeland, MI
CPT
82950-LAB-GLUCOSE 1 HOUR TOTAL
LOINC
Glucose 1Hr PP: 1504-0
Beaker LOINC
GLUCOSE 1HR POST 50 GRAMS: 10449-7
Beaker Names
Beaker Procedure Name: GLUCOSE 1 HOUR POST 50 G
Beaker Display Name: Glucose Tolerance, 1 hour test, 50 g (Gestational Diabetes Screen)
BEAKER TEST NAME: GLUCOSE 1 HOUR POST 50 G
BEAKER TEST REPORT NAME: Glucose 1 hour Post 50 g
Beaker Synonyms
No synonym on file
Beaker Location, Container and Temperature
BW CHEMISTRY: GREEN LI HEPARIN PST TUBE R (Preferred)-Refrigerated
BW CHEMISTRY: GOLD TOP SST TUBE R (Acceptable)-Refrigerated
BL CHEMISTRY: GREEN LI HEPARIN PST TUBE R (Preferred)-Refrigerated
BL CHEMISTRY: GOLD TOP SST TUBE R (Acceptable)-Refrigerated
BR CHEMISTRY: GREEN LI HEPARIN PST TUBE R (Preferred)-Refrigerated
BR CHEMISTRY: GOLD TOP
SST TUBE R (Acceptable)-Refrigerated
GM CHEMISTRY: GREEN LI HEPARIN PST TUBE R (Preferred)-Refrigerated
GM CHEMISTRY: GOLD TOP SST TUBE R (Acceptable)-Refrigerated
KL CHEMISTRY: GREEN LI HEPARIN PST TUBE R (Preferred)-Refrigerated
KL CHEMISTRY: GOLD TOP SST TUBE R (Acceptable)-Refrigerated
LH CHEMISTRY: GREEN LI HEPARIN PST TUBE R (Preferred)-Refrigerated
LH CHEMISTRY:
GOLD TOP SST TUBE R (Acceptable)-Refrigerated
PH CHEMISTRY: GREEN LI HEPARIN PST TUBE R (Preferred)-Refrigerated
PH CHEMISTRY: GOLD TOP SST TUBE R (Acceptable)-Refrigerated
RC CHEMISTRY: GREEN LI HEPARIN PST TUBE R (Preferred)-Refrigerated
RC CHEMISTRY: GOLD TOP SST TUBE R (Acceptable)-Refrigerated
UN CHEMISTRY: GREEN LI HEPARIN PST TUBE R (Preferred)-Refrigerated
UN
CHEMISTRY: GOLD TOP SST TUBE R (Acceptable)-Refrigerated
ZH CHEMISTRY: GREEN LI HEPARIN PST TUBE R (Preferred)-Refrigerated
ZH CHEMISTRY: GOLD TOP SST TUBE R (Acceptable)-Refrigerated