Gestational Glucose Tolerance Diagnostic Test (Three-hour, ACOG Recommendations)

CPT: 82951; 82952
Print Share

Test Details

Synonyms

  • Glucose Tolerance, Gestational Diabetes (Fasting, One-hour, Two-hour, and Three-hour)

Test Includes

100-g glucose load; plasma glucose measured fasting, and at one, two, and three hours

Use

Diagnose gestational diabetes

Methodology

Enzymatic

Contraindications

Patient with known history of diabetes mellitus

Reference Interval

See table.

Specimen*

Plasma or Serum Glucose Level

(Carpenter and Coustan Conversion)

Plasma Glucose Level

(National Diabetes Data Group Conversion)

*The diagnosis of GDM can be made based on the result of the 100-gram, three-hour oral glucose tolerance test, for which there is evidence that treatment improves outcome. Either the plasma or serum glucose level established by Carpenter and Coustan or the plasma level designated by the National Diabetes Data Group is appropriate to use. A positive diagnosis requires that two or more high thresholds be exceeded. The Carpenter and Coustan conversion is used to establish LabCorp reference intervals.

Fasting

65−94 mg/dL

65−105 mg/dL

One-hour

65−179 mg/dL

65−190 mg/dL

Two-hour

65−154 mg/dL

65−165 mg/dL

Three-hour

65−139 mg/dL

65−145 mg/dL

Additional Information

In 2013,2 the American College of Obstetricians and Gynecologists (ACOG) recommended that all pregnant women be screened for gestational diabetes mellitus (GDM)—whether by patient history, clinical risk factors, or with a 50-gram, one-hour loading test at 24 to 28 weeks of gestation to determine blood glucose levels—and suggested relying on the result of the 100-gram, three-hour oral glucose tolerance test for diagnosis (often referred to as a "two-step" method).

The American Diabetes Association (ADA)1 released standards that vary from the ACOG recommendations. The ADA standards recommend a simplified "one-step" approach to the screen and diagnosis of gestational diabetes mellitus with a 75-gram, two-hour glucose tolerance test. The LabCorp test according to the ADA recommendations is Gestational Glucose Tolerance Screening and Diagnostics Test (Two-hour, ADA Recommendations) [101000].

Specimen Requirements

Specimen

Serum or plasma

Volume

1 mL serum or plasma each tube

Minimum Volume

0.5 mL serum or plasma each tube

Container

Gel-barrier tubes (4) or gray-top (sodium fluoride/potassium oxalate plasma) tubes (4)

Patient Preparation

For three days prior to the test, patients should eat an unrestricted diet of 150 or more grams of carbohydrate and be permitted unrestricted physical activity. Patients should be instructed to eat and drink nothing 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.

Collection

Draw a fasting blood sugar before administering 100-gram glucose, and draw blood at one, two, and three hours. The subject should remain seated and not smoke throughout the test. Submit 1 mL serum or plasma for fasting, one-hour, two-hour, and three-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 patient's name and collection time interval (ie, fasting, one-hour, two-hour, and three-hour).

Storage Instructions

Maintain specimen at room temperature.3

Stability Requirements

Temperature

Period

Room temperature

14 days

Refrigerated

14 days

Frozen

14 days

Freeze/thaw cycles

Stable x3

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, two-hour, and three-hour)

Clinical Information

Special Instructions

The ADA 2011 standards1 vary from the ACOG recommendations.2 See Additional Information below.

Footnotes

1. American Diabetes Association. Standards of Medical Care in Diabetes—2015: Summary of revisions. Diabetes Care. 2015 Jan; 38(Suppl 1):S4. 25537706
2. American College of Obstetricians and Gynecologists. Committee on Practice Bulletins—Obstetrics. Practice Bulletin N° 137: Gestational diabetes mellitus. Obstet Gynecol. 2013 Aug; 122(2 Pt 1):406-416. 23969827
3. LabCorp internal studies.

LOINC® Map

Order Code Order Code Name Order Loinc Result Code Result Code Name UofM Result LOINC
102004 Gestational Glucose Tolerance 102012 Glucose - Fasting mg/dL 1558-6
102004 Gestational Glucose Tolerance 102020 Glucose - 1 hour mg/dL 1501-6
102004 Gestational Glucose Tolerance 102038 Glucose - 2 hour mg/dL 1514-9
102004 Gestational Glucose Tolerance 102046 Glucose - 3 hour mg/dL 1530-5
102004 Gestational Glucose Tolerance 102047 Note: N/A
102004 Gestational Glucose Tolerance 102049 Gest Glucose Tolerance (4) N/A

For Providers

Please login to order a test.

 

© 2017  Laboratory Corporation of America® Holdings and Lexi-Comp Inc. All Rights Reserved.

CPT Statement/Profile Statement

The LOINC® codes are copyright © 1994-2017, Regenstrief Institute, Inc. and the Logical Observation Identifiers Names and Codes (LOINC) Committee. Permission is granted in perpetuity, without payment of license fees or royalties, to use, copy, or distribute the LOINC® codes for any commercial or non-commercial purpose, subject to the terms under the license agreement found at https://loinc.org/license/. Additional information regarding LOINC® codes can be found at LOINC.org, including the LOINC Manual, which can be downloaded at LOINC.org/downloads/files/LOINCManual.pdf