CONTENTS. 1. Health and Safety Personnel and Training Requirements Purpose of the Test Principle Of the Test...

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1 Berkshire & Surrey Pathology Services CONTENTS 1. Health and Safety Personnel and Training Requirements Purpose of the Test Principle Of the Test Limitations and Contraindications Specimen Requirements, Means Of ID Required Equipment and Reagents Instructions for Performance of Examination Patient Preparation Procedure Interpretation of Results Recording Results References... 6 NB Anyone wishing to use this procedure should first check the website for the current version. Only the version on the website is authorised.

2 Berkshire & Surrey Pathology Services Glucose Tolerance Test (GTT) 1. HEALTH AND SAFETY GLP Colour Codes COSHH Information Good Laboratory Practice (GLP), Personal Protective Equipment(PPE), use of SOPs, clear work place Red = High hazard } Blue = Medium hazard } if GLP is followed Green = Low hazard } Substance COSHH Reference COSHH Score Hazard Requirement for Use Blood and body fluids COSHH MEDIUM Biological GLP/PPE Risk Assessment RA Reference Rating Requirement for Use Glucose Tolerance Test CIU-RSCH-RA Medium Avoid if fasting plasma glucose >8.0mmol/L, staff training & immunisation, needlestick reporting incident form & phlebotomy risk assessments 2. PERSONNEL AND TRAINING REQUIREMENTS Local guidance on personnel who may perform the test is available in the relevant phlebotomy SOPs. In CIU, the test can be carried out by a band 6 nurse with medical supervision. 3. PURPOSE OF THE TEST The oral glucose tolerance test (GTT) is used for the diagnosis of diabetes mellitus, as recommended by the World Health Organisation.

3 4. PRINCIPLE OF THE TEST Berkshire & Surrey Pathology Services The ability of the body to handle a glucose load provides an indication of the glycaemic status. 5. LIMITATIONS AND CONTRAINDICATIONS There are no contraindications to glucose tolerance testing. If fasting capillary blood glucose on a point of care testing device meter is <3.0 mmol/l or >10.0 mmol/l, do not proceed with the glucose load. A fasting venous plasma glucose should be sent to the laboratory for confirmation of the diagnosis. 6. SPECIMEN REQUIREMENTS, MEANS OF ID Glucose is measured on fluoride oxalate plasma (grey top vacutainer). Samples must be labelled in accordance with the SPS policy for Rejection of Samples (GEN- SPS-SOP REQUIRED EQUIPMENT AND REAGENTS Venesection materials 75 g anhydrous glucose

4 Berkshire & Surrey Pathology Services 8. INSTRUCTIONS FOR PERFORMANCE OF EXAMINATION 8.1 PATIENT PREPARATION The patient should be taking a normal, unrestricted diet, with a minimum of 150 g carbohydrate for at least 3 days prior to the test. The patient should fast overnight (10-14 hours), but can drink clear water freely. The patient should continue taking medications as usual unless otherwise instructed by their doctor (occasionally patients taking metformin for example will have the test carried out while off metformin). During the test the patient should be sitting down as exertion can give a misleadingly low 120 minute glucose value. Smoking is not permitted during the test. For patients who have undergone bariatric surgery, the GTT can be performed if a gastric band has been used. It is not appropriate to perform a GTT on patients who have had a gastric sleeve or by-pass surgery (Roux-en-y). A patient information leaflet is available for glucose tolerance tests (BIO-SPS-DOC-005). 8.2 PROCEDURE Check that the patient is fasted and explain the procedure to the patient. Take a capillary blood specimen, analyse the glucose level on the point of care device (as per the relevant Standard Operating Procedure) and record the level on the GTT worksheet, or request form as appropriate. If the capillary blood glucose level is <3.0 mmol/l or >10.0 mmol/l do not proceed with the glucose load but take a venous blood specimen and send to the laboratory for fasting glucose analysis. Explain to the patient that the test will not continue. If the capillary blood glucose is mmol/l, take a venous blood specimen and proceed with the test. Give 75g anhydrous glucose dissolved in ml water orally at 0 minutes. This should be consumed within a five minute period. o In children give glucose 1.75 g/kg ideal body weight to a maximum of 75 g.

5 Berkshire & Surrey Pathology Services At 2 hours, take a venous blood specimen. (In CIU, a capillary plasma specimen is also measured and recorded on the worksheet.) 9. INTERPRETATION OF RESULTS Normoglycaemia Fasting (mmol/l) 120 mins after glucose (mmol/l) Venous whole blood <5.6 <6.7 Capillary whole blood <5.6 <7.8 Venous plasma <6.1 <7.8 Impaired Fasting Glycaemia Venous whole blood 5.6 & <6.1 Capillary whole blood 5.6 & <6.1 Venous plasma 6.1 & <7.0 Impaired Glucose Tolerance Venous whole blood 6.7 & <10.0 Capillary whole blood 7.8 & <11.1 Venous plasma 7.8 & <11.1 Diabetes Mellitus Venous whole blood 6.1 <10.0 Capillary whole blood Venous plasma A diagnosis of diabetes mellitus cannot be made from a single glucose result in an asymptomatic patient: a minimum of two glucose results is required. The diagnosis may be made from a single glucose result if the patient is symptomatic. Venous plasma glucose measurements by the laboratory analyser should be used for diagnosis. The fasting capillary blood glucose measurement is used solely to assist with the decision whether to proceed with the glucose load. (In CIU, the two hour capillary glucose is used as a check to help confirm that the specimens sent for laboratory analysis are the correct way round.)

6 10. RECORDING RESULTS Berkshire & Surrey Pathology Services Capillary blood glucose levels measured by the point of care device should be recorded on the request form (or on the GTT worksheet in CIU). Laboratory results are recorded in the LIMS. For GTTs performed in CIU, the Consultant Chemical Pathologist issues a signed report to the requesting clinician. 11. REFERENCES Bouloux, PMG and Rees LH. Diagnostic tests in endocrinology and diabetes. Chapman and Hall Medical Press Definition and diagnosis of diabetes mellitus and intermediate hyperglycaemia. World Health Organisation, 2006.