Q: Is an OGTT good enough for CF diabetes testing?

Glucose Tolerance DrinkJamie, a 13-year-old girl with cystic fibrosis (CF), has been referred to the Paediatric Diabetes clinic because of an abnormal oral glucose tolerance test (OGTT) in her recent CF Annual Review. It showed impaired glucose tolerance. Continuous glucose monitoring system (CGMS) over three days showed normal fasting and pre-prandial glucose but frequent post-prandial glucose excursions between 11.1 mmol/l and 16.0 mmol/l. In retrospect, although Jamie‚Äôs previous OGTT carried out at Annual Review were normal, her lung function had gradually deteriorated over the past three years. This had been attributed to increasing episodes of infective exacerbations. You wondered for how long Jamie has had abnormal glucose metabolism which had gone undetected in her previous OGTT.The cut-offs which turn a test, especially one with a ‘continuous outcome’ from negative to positive are frequently debated… and with good reason. Those who see the ‘late’ diagnoses wish for greater sensitivity, but those who repeatedly see the fear produced by a false positive wish for better specificity. Underlying it all are values which are often decided by the most statistically attractive cut point, rather than an appreciation the the costs and benefits (in financial, clinical resource and patient experience)
of the effects the statistics imply.

What about here – is the OGTT just too coarse a measure for the job of detecting CF induced diabetes? Ngee Lek and Carlo L Acerini from Cambridge (UK) have set themselves the task of answering the question.

Acknowledgement: Image from gisarah under CreativeCommons2.0

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