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Test Name:
Glucose Tolerance, 2-Hour, Gestational (24-28 weeks), with 75g Glucose Load

• SBMF No:
  29054
• Performance Lab Name:
  Automated Lab
• Test Mnemonic:
  GTT2 75G
• ABN:
  Not required
• CPT Code:
  82951
• LOINC Code:
  12646-6; 1518-0; 1558-6
• Test Includes:
  Fasting glucose test result
  75 g glucose dose
  1- and 2-hour post-glucose test results (3 samples total)
• Also Known As:
  Gestational (24-28 weeks) Glucose Tolerance Test
  Pregnancy Glucose Tolerance
• Spec Type:
  Plasma
• Spec Container:
  Light green top (PST) tube
• Alt Spec Type:
  Plasma
• Alt Spec Container:
  Gray top (fluoride/oxalate) tube
  Note: Although not preferred, serum samples are acceptable, but must be removed from cells within 60 minutes of collection and refrigerated
• Pref Vol:
  1.0 mL
• Min Vol:
  0.3 mL
• Fasting:
  Yes
• Patient Prep:
  Fasting at least 8 hours; 12-hour fast is preferred; fasting should not exceed 14 hours
• Spec Collect:
  

  Routine venipuncture
  Collect at specified times:

  • Fasting sample (pre-glucose dose)
  • 1- and 2-hour samples (post-glucose dose)

• Spec Process:
  

  PST or gray top tubes:

  – Promptly centrifuge 15 minutes and refrigerate

  Gold top or red top tubes:

  – Clot 30 minutes
  – Promptly centrifuge 15 minutes
  – Within 60 minutes of collection, transfer serum to separate plastic tube and refrigerate

• Spec Store Transport:
  Refrigerated
• Spec Stability:
  1 week refrigerated (2-8°C)
• Spec Reject:
  Plasma (serum) in contact with RBC more than 1 hour
• Spec Remarks:
  For diagnostic purposes, plasma samples are recommended, rather than serum. Plasma glucose results are generally 5% lower than serum and the cutoff values for diagnostic testing, as recommended by the Hyperglycemia and Adverse Pregnancy Outcome (HAPO) study, were established using plasma. The reference ranges posted on SBMF glucose reports are also based on plasma studies.

  Urine specimens will not be routinely collected and tested for the tolerance test

• Methodology:
  Photometric
• Use:
  Establish the diagnosis of diabetes mellitus in the pregnant patient
• Reference Range:
  GTT with a 75g glucose load at 24 to 28 weeks gestation
  Diagnostic of gestational diabetes if one or more of glucose results meet the following criteria:

  Fasting 1 hour 2 hour

  >= 92 mg/dL >= 180 mg/dL >= 153 mg/dL

  Reference: International Association of Diabetes and Pregnancy Study Groups Recommendations on the Diagnosis and Classification of Hyperglycemia in Pregnancy. Diabetes Care, vol 33, No 3, March 2010

• Day Run:
  Mon-Sat
• Time Run:
  As received
• Time Reported:
  Same day
• Test Type:
  OBSTETRIC-NEONATAL