Oral Glucose Tolerance Tests (OGTTs) in Primary Care: a reliable test?

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Oral Glucose Tolerance Tests (OGTTs) in Primary
Care a reliable test?

• Bowles S.A.1, Ewins D.2, Goenka N.2, Heathcote
  K.1, Worth R.2
• 1Countess of Chester Hospital, Chemical
  Pathology, 2Countess of Chester Hospital,
  Diabetes and Endocrinology,

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Background

• Oral Glucose Tolerance tests (OGTTs) are
  performed in Primary Care practices to confirm or
  exclude
• Diabetes Mellitus / Impaired Glucose Tolerance /
  Impaired Fasting Glycaemia.
• OGTTs must be performed according to the WHO
  protocol
• In 2004, The Diabetes Unit in COCH issued
  guidelines on the performance and interpretation
  of these test
• Having scrutinised requests for OGTTs, it was
  suspected that the standards for the performance
  of these tests were not being uniformly adhered
  to.

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Audit To determine whether local Primary Care
practices are following appropriate protocols for
the performance of OGTTs

• A survey, in the form of a questionnaire, was
  sent out to the 47 Primary Care practices in our
  local area.
• The Clinical Audit Department collected the
  returned forms and collated the data provided.
• 30 forms were returned a return rate of 64.

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OGTTs in house or patients sent elsewhere?

• Patients from the 10 practices, which reported
  that the tests were done elsewhere, came to the
  Countess of Chester or one of 3 other local
  hospitals.
• The remainder of the data is derived from the
  responses from the 18 practices, which reported
  performing OGTTs in house.

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Period of fasting advised?

• Written information given to patients in 61 of
  Practices
• explanation of test
• preparations required
• Period of fasting advised before the OGTT was
  variable
• For most practices, fell within the 10-14 hours
  of the WHO protocol.

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Nature of standard glucose load?

• Volume used varied considerably
• Potential difference in the glucose load of over
  20g between the highest and lowest volumes.

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Nature of standard glucose load?

• It was not obvious that a specific preparation
  was being consistently used
• In 6 practices, the patients were requested to
  bring their own!

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Rest during test?Handling of blood specimens?

• According to the OGTT protocol, patients should
  rest during the test
• Only 56 of respondents reported that they asked
  the patient to remain in the Practice until after
  the 2-hour blood specimen is collected.
• All the practices did send their specimens to our
  Laboratory for testing
• Fasting and 2-hour specimen were sent together as
  a single batch.

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Results from OGTTs

• OGTTs over a 12-month period
• 3 Practices using 380 / 381ml Lucozade
• Total 135 patients
• 1 Practice using 450 ml
• Total 120 patients
• T-test
• Fasting blood glucose
• P 0.364
• 2-hour glucose
• P 0.016

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Conclusion (1)

• Despite the provision of local guidelines, OGTTs
  are notperformed in a uniform fashion in local
  Primary Care practices.
• The standard glucose load was evidently
  anything but standard (ranging from approximately
  63 85g)
• this is likely to have an impact on the
  diagnostic category to which patients are
  assigned.
• Lucozade is convenient and palatable as the
  glucose solution but
• Changes in the formulation - the volume required
  to provide 75g of glucose can vary.
• It is necessary to keep up to date with any
  changes in its production to ensure the glucose
  load provided is correct.

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Conclusion (2)

• The 2004 local guidelines stipulated 420 ml
  Lucozade Original
• In April 2008, the Lucozade website indicated
  that, if using Lucozade Energy Original, the
  appropriate volume was 394ml.
• From early May 2008, the energy content was being
  reduced
• the volume required increased to 410ml
• transition period when both variants would be
  available
• Practitioners advised to check the label to
  confirm which formulation was being used.
• Other preparations of Lucozade (eg Orange, Lemon,
  Tropical etc) contain different concentrations of
  carbohydrate
• need to specify Lucozade Original or, as it is
  now known, Lucozade Energy Original.

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Conclusion (3)

• The guidelines for the performance of the OGTT
  are being revised, reiterating the need to follow
  the WHO protocol.
• Considering the variation in volumes of Lucozade
  being used by Practices, it seems unlikely that
  information regarding the formulation is being
  sought or the need to do so recognised.
• To obviate the need to keep up to date with
  Lucozades formula changes, the new guidelines
  will stipulate that the preparation Polycal
  should be used as the glucose load.
• It is intended that the audit will be repeated 12
  months after the issue of the new guidelines.