Specimen Collection

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.

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PROCEDURE for performing a Glucose tolerance test:

Note: Two bloods are to be collected a) Fasting blood (before glucose drink) b) 2 hours post-glucose drink

1. For three days prior to the test the patient must be on a diet containing more than 150 g of carbohydrate daily.

2. Drug therapy should be stopped on the morning of the test.

3. The patient must not smoke during the test.

4. Following a fast of at least 8h, an oral dose of glucose is given.

Dose:

Adult: 75 g anhydrous glucose in 300-350 mL water

Pregnant Women: 75 g anhydrous glucose in 300-350 mL water

Also see Gestational Diabetes for details of the non-fasting 50 g oral glucose screening test (Polycose test)

Children: 1.75 g/kg of body weight (maximum dose 75g)

5. Two blood specimens are collected: fasting, and two hours after glucose.

4 mL Fluoride Blood
Turnaround Time: Within 3 hours
Diagnostic Use and Interpretation

INTERPRETATION:

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.

Contact Information

Emails to chemicalpathologist@adhb.govt.nz will receive priority attention from the on-call chemical pathologist.

If the query concerns a specific patient please include the NHI number in your email.

If email is not a suitable option, please contact the on-call chemical pathologist via Lablink (Auckland City Hospital ext. 22000 or 09-3078995).

Individual chemical pathologists may be contacted but will not be available at all times.

After-hours : contact Lablink (Auckland City Hospital ext. 22000 or 09-3078995) or hospital operator for on duty staff after hours.

Dr Samarina Musaad (Clinical Lead) : SamarinaM@adhb.govt.nz ext. 22402

Dr Cam Kyle: CampbellK@adhb.govt.nz ext 22052

Dr Weldon Chiu: WeldonC@adhb.govt.nz ext. 23427

Dr Campbell Heron: CHeron@adhb.govt.nz ext. 23427

Dr Sakunthala Jayasinghe: Sakunthala@adhb.govt.nz ext. 23427