GPs may be missing a ‘significant proportion’ of diabetes and impaired glucose tolerance cases because they are being encouraged to use the wrong test in women who have had gestational diabetes, UK researchers have warned.
The study – presented at the Diabetes UK conference in Glasgow this week – says NICE guidelines on gestational diabetes should be changed to ensure all women receive an oral glucose tolerance test (OGTT).
Current guidelines specifically rule out the ‘gold standard’ test and instead recommend a fasting glucose test six weeks after delivery and annually thereafter.
The study collected data on all women with gestational diabetes attending a clinic over seven years. The 147 women identified were given both tests postpartum and the results were compared.
Fifty-two of the 147 women had a persistent abnormality in glucose metabolism. Twenty-three had impaired fasting glycaemia, 21 had impaired glucose tolerance and eight women had diabetes.
According to a cut-off of 7.0 mmol/l for diabetes, one of the eight women with diabetes (12.5%) and all 21 women with impaired glucose tolerance would have been missed if a fasting blood glucose test alone was used.
In contrast, no cases of diabetes would have been missed if an OGTT were performed; however, 16 (76%) cases of impaired glucose tolerance would have been missed.
Dr Franklin Joseph, study lead and a consultant in diabetes and endocrinology at the Countess of Chester NHS Foundation Trust, said both tests should be used routinely in all cases of gestational diabetes, but added: ‘An OGTT in all women with gestational diabetes remains the gold standard test.’
‘Postnatal fasting blood glucose alone is inadequate to identify all women with diabetes.’
Professor Philip Home, professor of diabetes medicine at Newcastle University, said: ‘NICE is wrong here. Fasting plasma glucose is not a suitable screening test and has been shown many times to miss people with diabetes.’
‘There is no absolute consensus on how to follow high risk people, which is what ex-gestational diabetes women are, for diabetes, but many would now suggest that yearly HbA1c is preferable to repeated challenge tests such as the OGTT.’
Dr Colin Kenny, a GP in Dromore, County Down and a member of the Primary Care Diabetes Society Steering Committee, said the study’s proposals were impractical and agreed HbAlc testing may be the better option: ‘There are quite a few issues around doing OGTT in practice, as it is hard to standardise them and they are often done poorly in practice.
Current NICE guidance
· Women who were diagnosed with gestational diabetes should have their blood glucose tested to exclude persisting hyperglycaemia
· They should be offered lifestyle advice (including weight control, diet and exercise) and offered a fasting plasma glucose measurement (but not an OGTT) at the six-week postnatal check and annually thereafter
Source: NICE clinical guideline 063, March 2008