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Gestational Glucose Tolerance Screening and Diagnostic Test (Two-hour, ADA Recommendations)
- Glucose Tolerance Test, Gestational (Fasting, One-hour, and Two-hour)
Expected Turnaround Time
Turnaround time is defined as the usual number of days from the date of pickup of a specimen for testing to when the result is released to the ordering provider. In some cases, additional time should be allowed for additional confirmatory or additional reflex tests. Testing schedules may vary.
Serum or plasma
1 mL serum or plasma each tube
0.5 mL serum or plasma each tube
Gel-barrier tubes (3) or gray-top (sodium fluoride/potassium oxalate plasma) tubes (3)
Draw a fasting blood sample before administering glucose. Administer a 75-gram glucose and draw blood after one hour and two hours. The patient should remain seated throughout the test. Submit 1 mL serum or plasma for fasting, one-hour, and two-hour specimens. Separate serum or plasma from cells within 45 minutes of venipuncture. Gray-top tubes only, may be submitted without centrifugation. Label each tube with the patient's name and collection time interval (ie, fasting, one-hour, and two-hour).
Maintain specimen at room temperature.1
Patient should be active and eat a regular diet that includes at least 150 grams of carbohydrate daily for three days prior to the test. The patient should be instructed not to eat or drink anything except water for at least eight hours and not more than 14 hours before the test. Patients should also be advised to discontinue, whenever possible, all nonessential medication that can affect glucose metabolism at least three days before testing.
Causes for Rejection
Frozen gray-top tube (frozen plasma from gray-top is acceptable); stressed patient (surgery, infection, corticosteroids) should not have GTT; specimens not labeled with collection time intervals (i.e., fasting, one-hour, and two-hour)
Screening and diagnosis of gestational diabetes
Specimen (Two-hour GGT Test)*
*A positive diagnosis requires that only one of the high thresholds be exceeded.
American Diabetes Association Standards of Medical Care in Diabetes recommendations:2
• Screen for undiagnosed type 2 diabetes at the first prenatal visit in those with risk factors using the standard nongestational diagnostic criteria.
• In pregnant women not known to have diabetes, screen for gestational diabetes mellitus (GDM) at 24 to 28 weeks of gestation using the Gestational Glucose Tolerance Screening and Diagnostic Test (Two-hour, ADA Recommendations).
• Screen women with GDM for persistent diabetes 6 to 12 weeks postpartum using nonpregnant OGTT criteria, hemoglobin A1c(102525), fasting plasma glucose (001818), or a 75-gram, two-hour oral glucose tolerance test (101200), two specimen WHO glucose tolerance test).2 Women diagnosed with GDM should, in subsequent pregnancies, be re-evaluated.
• Women with a history of GDM should have lifelong screening for the development of diabetes or prediabetes at least every three years.
Note: The American Diabetes Association (ADA) released recommendations that vary from the American College of Obstetrics and Gynecology (ACOG) recommendations. The ADA recommends the current (101000) simplified “one-step” for screening and diagnosis of gestational diabetes mellitus using a 75-gram, two-hour glucose tolerance test. The ACOG recommendations3 use a 100-gram, three-hour glucose tolerance test (102004).
|Order Code||Order Code Name||Order Loinc||Result Code||Result Code Name||UofM||Result LOINC|
|101000||Gestational 2 hour GTT||011121||Glucose, Fasting||mg/dL||1558-6|
|101000||Gestational 2 hour GTT||011122||Glucose, 1 hour||mg/dL||1507-3|
|101000||Gestational 2 hour GTT||011123||Glucose, 2 hour||mg/dL||1518-0|
|101000||Gestational 2 hour GTT||103033||Glucose (3)||N/A|