Download SOP - GTT IN PREGNANCY

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Pathology at the Royal Derby Hospital
Glucose Tolerance Test in Pregnancy
Standard Clinical Guideline
Chemical Pathology Department
Document Code: CHISCG9
Valid until : 31st March 2015
Glucose Tolerance Test in Pregnancy
INTRODUCTION
The term gestational diabetes mellitus (GDM) is restricted to women in whom the
onset or recognition of diabetes mellitus first occurs during pregnancy. Women with
glucose intolerance during pregnancy have an increased life time risk of developing
diabetes mellitus in later life, as well as there being an increased risk of macrosomia
and neonatal hypoglycaemia in the baby.
The oral glucose tolerance test (GTT) is used in the investigation of GDM. 75g of
anhydrous glucose (or its equivalent) in a final volume of 300 mL is used as
recommended by the WHO Expert Committee on Diabetes Mellitus.
All glucose values in this document refer to venous plasma glucose levels. Glucose
results obtained from “near patient” testing strips should not be used in the diagnosis
of gestational diabetes.
INDICATIONS
1)
Screening for gestational diabetes:
a) Urine should be tested for glycosuria at every antenatal visit.
b) Laboratory glucose measurements should be made:
i) Whenever glycosuria (1+ or more) is detected
ii) At 28 weeks gestation.
If the random glucose concentration is >11 mmol/L the diagnosis of diabetes is
confirmed and the glucose tolerance test is unnecessary. Refer the patient to the
Consultant Diabetologist in Diabetic Obstetric Clinic (DOC).
2)
A glucose tolerance test is indicated if:
a) The random plasma glucose concentration is ≥6 but ≤11 mmol/L.
b) There is a strong clinical indication of the possibility of GDM (see
indications for risk factor screening contained in the ‘Diabetes Services in
Obstetrics’ guideline OBS/Diabetes/10:2011/D1).
CONTRAINDICATIONS
None
CHISCG9 - Glucose Tolerance Test in Pregnancy
Revision No 6
Expiry Date: 31st March 2015
Authorised by Julia Forsyth
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CG-Path /2006/02
SIDE EFFECTS
Occasionally nausea, vomiting or diarrhoea as the glucose drink is hyperosmolar.
PRECAUTIONS
None
PREPARATION
Planning
A GTT is an outpatient procedure carried out jointly between the Antenatal Unit and
the Phlebotomy Department at RDH. A GTT can be performed Monday to Friday
morning by appointment with the Antenatal Unit.
Patients using this service may be either:
a) Already booked in at the Antenatal Clinic
b) Referred by their Midwife/GP.
A GTT can be carried out at Clinic F at the LRCH but where possible, it is preferable
that the patient has the test at the Antenatal Unit.
Patient
The patient should have a normal diet containing more than 150g carbohydrate daily
for three days prior to the test.
Guide to the carbohydrate content of some common foods
Food item
Approximate carbohydrate content (g)
1 Slice of bread
Tablespoon of rice
Egg sized potato
2 Weetabix
Packet of crisps
10
12
10
30
15
All medication the patient is receiving should be noted on the request form.
The patient should fast from 10.00 p.m. the previous evening to give a minimum 10
hour fasting period. Water is permitted. The procedure should start between 8.30
am and 10.00 am.
CHISCG9 - Glucose Tolerance Test in Pregnancy
Revision No 6
Expiry Date: 31st March 2015
Authorised by Julia Forsyth
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Uncontrolled when printed
CG-Path /2006/02
Equipment
a) For use in GP surgeries
Glucose - dissolve 1 packet of dextrose (82.5g glucose monohydrate) in 250
mL water, this gives a final volume of 300 mL. This is equivalent to 75g
anhydrous glucose. Note the dextrose is lemon flavoured to make it more
palatable. Chemical Pathology, RDH obtains the glucose from pharmacy and
provides supplies for GPs. Note: “Glucose BP” is glucose monohydrate.
b) For use in LRCH and RDH
Polycal - this is a carbohydrate drink based on maltodextrin a partial
hydrolysate of corn starch. It is supplied by Cow and Gate in 200 mL bottles.
Only 113 mL is required for each patient. This is equivalent to 75g anhydrous
glucose. If 3 patients are being tested 2 bottles are sufficient.
Measure 113 mL Polycal into a special beaker and add water up to 200 mL
mark. Secure plastic cap firmly onto beaker, shake to mix. Polycal is now
ready.
Note:
A further 100 mL of water must be drunk by the patient to make the
final volume 300 mL.
c) Specimen tubes required
Each test requires two fluoride/oxalate tubes.
PROCEDURE
A. Procedure for Antenatal unit, RDH
a)
A fasting venous blood sample (minimum volume 1 mL in a
fluoride/oxalate tube) is taken in the Phlebotomy Department. The
patient returns to the Antenatal Unit.
b)
The Polycal drink is given in the Antenatal Unit and should be taken
within five minutes followed by 100 mL of water. This is time “0 hours”.
c)
At 2 hours after taking the Polycal drink, a venous blood sample
(minimum volume 1 mL in a fluoride/oxalate tube) is taken in the
Phlebotomy Department.
d)
Samples must be clearly labelled with the patient’s name, date and the
time the sample was taken.
CHISCG9 - Glucose Tolerance Test in Pregnancy
Revision No 6
Expiry Date: 31st March 2015
Authorised by Julia Forsyth
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Uncontrolled when printed
CG-Path /2006/02
B. Procedure for LRCH Phlebotomy Clinic or GP Surgeries
Ideally GTTs on pregnant patients should be carried out in the antenatal unit
at RDH, but if this is not feasible the procedure as summarised below can be
carried out in a phlebotomy clinic.
Table 1 - Summary of GTT procedure:
Time
Fasting
sample
0 hours
2 hours
sample
Event
Minimum volume 1 mL venous blood in fluoride/oxalate tube.
Give Polycal drink, to be drunk within 5 minutes, followed by 100
mL of water.
Minimum volume 1 mL venous blood in fluoride/oxalate tube.
The patient may drink additional water during the test and should be seated quietly
throughout the test. Smoking or eating is not permitted during the test. The test is
completed when the 2 hour blood sample has been collected.
INTERPRETATION
Table 2 - Interpretation of the 75 g oral glucose tolerance test during pregnancy:
Fasting Glucose
mmol/L
2 Hour
Glucose
mmol/L
<7.8
≤5.5
5.6 – 6.0
and/
or
7.8 – 8.2
> 6.0
and/
or
>8.2
Diagnosis
Action
Normal
None
“Borderline”
(Gestational
diabetes but low
risk)
Gestational
diabetes
Review case notes in
line with management
guidelines
(OBS/10:2011/D1)
Refer patient to next
DOC
TURNAROUND TIME
24 hours
CHISCG9 - Glucose Tolerance Test in Pregnancy
Revision No 6
Expiry Date: 31st March 2015
Authorised by Julia Forsyth
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CG-Path /2006/02
REFERENCES AND FURTHER READING
1.
WHO Expert Committee on Diabetes Mellitus. WHO Technical Report Series
727,1985.
2.
Jardine Brown et al. Report of the Pregnancy and Neonatal Care Group.
Diabetic Medicine 1996; 13: 543-553.
3.
American Diabetes Association Report of the Expert Committee on the
diagnosis and classification of diabetes mellitus. Diabetes Care 1997; 20:
1183-1197.
4.
Prevention of Diabetes Mellitus. WHO Technical Report Series (2000).
5.
Recommendations for the Management of pregnant women with diabetes
(including gestational diabetes).
Diabetes Care Advisory Committee,
Diabetes UK (July 2001). www.diabetes.org.uk
6.
Screening for Gestational Diabetes OBS/01:06/D1a
7.
Comparison of international and New Zealand guidelines for the care of
pregnant women with diabetes. Diabetic Medicine 2006; 23(5): 460-468.
8.
Management of Diabetes, A National Guideline (No 55).
Intercollegiate Guidelines Network (Nov 2001).
Reviewed by:
SCG group
SCG group
SCG group
SCG group
Helen Seddon
Helen Seddon
R Stanworth/H Seddon
Date:
September 1999
August 2001
November 2003
March 2006
August 2008
December 2009
March 2012
CHISCG9 - Glucose Tolerance Test in Pregnancy
Revision No 6
Expiry Date: 31st March 2015
Authorised by Julia Forsyth
Valid Until:
August 2001
October 2003
October 2005
October 2007
October 2009
December 2011
March 2015
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