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| GLUCOSE TOLERANCE TEST |
| Department: | Biochemistry |
| Alternate Names for Test: |
GTT OGTT ORAL GLUCOSE TOLERANCE TEST |
| Specimen Collection Requirements: | |
| Patient Preparation: | NOTE: Glucose tolerance test is rarely indicated for diagnosis of type two diabetes, but is still required for diagnosis of Gestational diabetes. HbA1c is now the preferred diagnostic test for type two diabetes. However HbA1c measurements may be misleading in cases of haemoglobinopathy, increased red cell turnover or post transfusion. Contact Laboratory for appointment. Must be FASTING for at least 8-14 hours (water allowed) prior to test. Patient should allow a minimum of two hours. Test usually commenced before 9:00 am due to diurnal variation. PRECAUTIONS:(The commercial glucose used contains Carbonated water, glucose, food acid(330), flavour preservative(202, 211). Please indicate if patient has a known allergy to these food additives so an alternative glucose load can be used. |
| Phlebotomist Instructions: | Refer to procedure in Phlebotomy Manual For adults and children 43 kg and over a glucose load of 75g is given as per instructions found in the procedures (above). For children under 43kg a load of 7ml per kg is given. |
| Patient Instruction Sheet: | |
| Sample Type: |
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| Sample Type Notes: | 2x 2ml blood, Fluoride (grey top) tube collected fasting and at 2 hours |
| Minimum Sample Volume: | 1mL whole blood per sample |
| Additional Information: | NOTE: Test can be extended to 3, 4 or 5 hours if specifically requested. Take consecutive one hourly glucose blood |
| In the Lab: | |
| Lab Test Code: | GTTSTD |
| Testing Schedule: | Analysed daily, Monday - Friday |
| Turnaround Time: | Daily, Monday - Friday |
| Reference Interval & Interpretation: | NOTE: Glucose tolerance test is rarely indicated for diagnosis (except in Gestational diabetes). HbA1c is now the preferred diagnostic test for type 2 diabetes. Fasting 3.0- 6.0 mmol/L 2 hour < 7.8 mmol/L Diabetic Range: 2 hour >= 11.1 mmol/L Impaired Range: Fasting < 7.0 mmol/L and 2 hr hour level 7.8-11.0 mmol/L Diabetes must also be diagnosed if fasting glucose is >= 7.0 mmol/L with symptoms of diabetes or if >= 7.0 mmol/L on two occasions without symptoms. Impaired fasting glycaemia is present when glucose is 6.1-6.9 mmol/L and 2 hour level is <7.8 mmol/L (if measured). GTT may be prolonged (up to 5 hours) where reactive hypoglycaemia is suspected. GTT is not indicated for known diabetes. Refer also Glucose Tolerance Test (Gestational). |
| Method: | Roche Modular P800, Glucose Hexokinase |
| Units of Measurement for Test: | mmol/L |
| Stability Time Limit for Add-On Tests: | 1 day |
| Reflex / Confirmatory Tests: | A confirmatory/reflex ketone test may be generated. Additional charges may incur. |
| Link to Application and Diagnostic Use Website: | http://www.rcpamanual.edu.au/index.php?option=com_pttests&view=tests&Itemid=77 |
| Notes: | Specimen Collection Instructions: 1. Collect the Fasting glucose blood, time and date the specimen. Label #1 2. Give the patient the glucose load of 75g GLUCAID (0.25g/mL) or (7mL/kg) for children. NOTE: at 43 kg and over, the full 75g load is given) and fill in history sheet. 3. The patient is not to leave the laboratory or eat, drink or smoke during the test. 4. Take the 2 hour glucose blood sample, time and date the specimen. Label #2 NOTE: Test can be extended to 3, 4 or 5 hours if specifically requested. Take consectutive one hourly glucose blood. |
| Contact Details: | |
| Lab Contact: | Max Reed and Dr Michael Crooke |
| Department Name: | Biochemistry |
| Phone: | (04) 3815900 ext 850 |
| Fax: | (04)3815985 |
| Email: | mreed@apath.co.nz |
Test Information last updated on 13/08/2012
Website last updated on 17/06/2013 09:00
1x Grey (Fluoride/Oxalate) tube 2.0mL