Gestational Diabetes testing procedures are in need of an overhaul for accurate diagnosis

Photo of pregnant woman

Along with the excitement and joy of pregnancy there also comes the many medical visits and routine testing to ensure the health and safety of mother and baby.  Sometime between week 24 and 28 of pregnancy, mothers undergo a test for Gestational Diabetes – a test to detect abnormally high levels of glucose in the blood.

Gestational Diabetes occurs when the body is unable to maintain normal blood glucose levels due to inadequate insulin production and/or action during pregnancy. If not detected and managed, Gestational Diabetes can result in adverse pregnancy outcomes, including macrosomia (overweight babies at birth), neonatal hypoglycaemia (low blood glucose) and high Caesarean section rates. The condition also increases the risk for preeclampsia which results in high maternal blood pressure and organ dysfunction– putting the lives of mother and baby at risk. 

In 2001, the percentage of women with Gestational Diabetes in Australia was a relatively small 5%. However, since then, the case rate has increased to almost 15% making it the fastest growing type of diabetes in Australia.

New research from the ANU Medical School has uncovered that the percentage of cases is likely even higher than the current 15%.  Professor Julia Potter and colleagues, found that simple changes to the way the blood samples of pregnant women were handled (preanalytic processing) could increase the number of cases of Gestational Diabetes identified.

Current international guidelines for testing of Gestational Diabetes recommend that the blood sample is placed in an ice slurry and centrifuged (ie. the blood sample is spun to separate the cells) within 30 minutes of collection. Doing so keeps the glucose levels in the blood at a concentration that provides an accurate diagnosis. Even before 30-minutes, glucose loss occurs through blood cells using it for energy (glycolysis). In the study, samples centrifuged within 10-minutes of collection increased the rate of diagnosis from 11.6% to 20.6%, as there was no time for glycolysis to lower the glucose concentration.

Due to circumstances the recommended ice slurry and 30-minute centrifugation guideline can’t always be followed. For example, in rural communities there are no pathology labs close by and the sample must be sent off before centrifugation for testing. This delay is leading falsely low glucose levels to undetected cases.

Senior author Professor Chris Nolan said, “The underlying problem is that the sodium fluoride in the tubes most commonly used in Australia and internationally is slow to stop glycolysis. An alternative would be to use citrate in the tubes, as it immediately stops glycolysis. Use of citrate tubes would stabilise the glucose concentration and increase accuracy of Gestational Diabetes testing irrespective of the time taken to centrifugation. Before adopting citrate tubes widely, however, some additional research is required.”

“This is a real problem leading to unreliable Gestational Diabetes test results in many countries around the world.  I’d very much like to see international consensus on an improved protocol for preanalytic blood sample handling that ensures accurate diagnosis of Gestational Diabetes no matter where the test is performed. All pregnant women tested deserve a test result that they can fully trust.”