Glucose Tolerance Test (Blood)

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Auckland Te Toka Tumai

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Glucose Tolerance Test (Blood)

Testing Laboratory

Auckland Te Toka Tumai | Auckland Hospital

Department

Chemical Pathology

Delphic Registration Code (Alpha Code)

GTTF (Fasting) / 0042. GTT2 (2 Hrs) / 0041

Test Code (Numeric Code)

0042

Laboratory Handling

Phlebotomy

See additional information for GTT procedure. Note: Two bloods are to be collected a) Fasting blood (before glucose drink) b) 2 hours post-glucose drink.

Transport

Fluoride tubes should be used if specimens are expected to take >1 hour to arrive at the lab.

Registration

If registration form has glucose tolerance test and serum glucose selected/written only register for glucose tolerance test.

Test Adds Requirement

PST/Heparin tubes are acceptable if Fluoride tube is not available. Please check sample collection time prior to test add.

Sample Stability

See glucose test for details.

Associated Tests

Glucose (Blood)

Synonyms

GTT

Turnaround Time

3 hours

Specimen Type

Plasma

Specimen Requirements

Tube/Container Type:

Preferred

Fluoride (Grey Cap)

Acceptable

Lithium Heparin - Non-gel (Green Cap)
Lithium Heparin PST- Gel (Light Green Cap)
Plain (Red Top)
SST II (Gold Cap)

Preferred Sample Volume (ml)

Minimum Sample Volume (ml)

Paediatric Specimen Requirements

Tube/Container Type:

Preferred

Lithium Heparin PST- Gel (Light Green Cap)

Preferred Sample Volume (ml)

0.5

Minimum Sample Volume (ml)

0.5

Pre-testing Requirements

The following criteria are from the Australian Diabetes Society, NZ Society for the Study of Diabetes, the Royal College of Pathologists of Australasia, and the Australasian Association of Clinical Biochemists (Ref: New classification and criteria for diagnosis of diabetes mellitus. PG Colman et al. MJA 1999; 170: 8)

Prior to commencement of the test, a random or fasting blood glucose must be tested.

The glucose tolerance test must NOT be performed if:
1. The fasting glucose is >9 or random glucose >13 mmol/L
2. The patient is very ill (the test is invalid in the presence of intercurrent illness or stress such as that induced by trauma, surgery etc.).
3. The patient is a known diabetic.

Diagnostic Use

A patient is DIABETIC if they have:

Symptoms plus:
a. A random glucose > 11.1 mmol/L orb. A fasting glucose >7.0 mmol/L

No symptoms plus:
a. Two random glucoses >11.1 mmol/L or
b. Two fasting glucoses >7.0 mmol/L or
c. One random glucose >11.1 mmol/L and one fasting glucose >7.0 mmol/L or
d. In a Glucose Tolerance Test:
A fasting glucose >7.0 mmol/L and / or a 2 hour glucose >11.1 mmol/L

IMPAIRED GLUCOSE TOLERANCE (IGT) is defined as:
In a Glucose Tolerance Test:
A fasting glucose < 7.0 mmol/L and a 2 hour glucose > 7.8 mmol/L and < 11.1 mmol/L.

IMPAIRED FASTING GLYCAEMIA (IFG) is defined as:
A fasting glucose > 6.1 mmol/L and < 7.0 mmol/L
2 hour post glucose load (if measured) < 7.8 mmol/L

GESTATIONAL DIABETES

Pregnant women may be screened at 24 – 28 weeks gestation with a 50g oral glucose load (non-fasting). Blood is taken at 1h after the glucose load; a glucose of > 7.8 mmol/L is abnormal (this was previously called the Polycose test).

1. Those patients with a normal result but with risk factors should be re-screened at 32 – 34 weeks.
2. Women with an abnormal screen test should undergo a fasting 2 hr Glucose Tolerance Test, with a 75 g glucose load. This should be interpreted according to the following criteria:

NOTE: Only the fasting and 2 hour values are used for the interpretation of gestational glucose tolerance tests consistent with the recommendations of the New Zealand Society for the Study of Diabetes.

Interpretation
a) If either fasting >5.5 mmol/L or 2 hour >9.0 mmol/L: Gestational diabetes is confirmed
b) If both fasting < 5.5 mmol/L and 2 hour < 9.0 mmol/L: Normal pregnancy GTT

Glucose tolerance may deteriorate during pregnancy so repeat GTT in four weeks may be warranted if it is clinically indicated.
Clinical indications (risk factors) include a history of macrosomia, obesity, strong family history of gestational diabetes or diabetes, and a past history including previous GDM, macrosomia or intrauterine death or still-birth.See glucose test for details.

Test Method

See Glucose (Blood)

Uncertainty of Measurement

See Glucose (Blood)

Last updated: 10/08/2026

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A B C D E F G H I J K L M N O P Q R S T U V W X Y Z #

Testing Laboratory

Department

Delphic Registration Code (Alpha Code)

Test Code (Numeric Code)

Laboratory Handling

Phlebotomy

Transport

Registration

Test Adds Requirement

Sample Stability

Associated Tests

Synonyms

Turnaround Time

Specimen Type

Specimen Requirements

Tube/Container Type:

Preferred

Acceptable

Preferred Sample Volume (ml)

Minimum Sample Volume (ml)

Paediatric Specimen Requirements

Tube/Container Type:

Preferred

Preferred Sample Volume (ml)

Minimum Sample Volume (ml)

Pre-testing Requirements

Diagnostic Use

Test Method

Uncertainty of Measurement

Contact Information

Enquiry Form

Search tests

Glucose Tolerance Test (Blood)

Overview

Testing Laboratory

Department

Delphic Registration Code (Alpha Code)

Test Code (Numeric Code)

Laboratory Handling

Phlebotomy

Transport

Registration

Test Adds Requirement

Sample Stability

Associated Tests

Synonyms

Turnaround Time

Specimen

Specimen Type

Specimen Requirements

Tube/Container Type:

Preferred

Acceptable

Preferred Sample Volume (ml)

Minimum Sample Volume (ml)

Paediatric Specimen Requirements

Tube/Container Type:

Preferred

Preferred Sample Volume (ml)

Minimum Sample Volume (ml)

Pre-testing Requirements

Referral

Clinical Information/Test Method

Diagnostic Use

Test Method

Uncertainty of Measurement

Additional Information

Contact Information

Contact Information

Enquiry Form

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