Standardising preanalytical conditions for gestational diabetes blood test
A working party of pathologists, clinicians and researchers are working towards an international study to improve the diagnosis of gestational diabetes mellitus (GDM). Formed by the RCPA, the Australasian Association for Clinical Biochemistry and Laboratory Medicine (AACB), the Australasian Diabetes in Pregnancy Society, and led by Professor Andrea Rita Horvath, NSW Health Pathology, the group aims to standardise the preanalytical protocols for oral glucose tolerance test (OGTT) blood samples used for GDM diagnosis.
Professor Christopher Nolan, Associate Director of Research at the ANU School of Medicine and member of the working party explains that the handling of OGTT blood samples needs to be standardised in order to improve diagnosis of GDM.
“In Australia, all pregnant women without known diabetes are recommended for an OGTT to screen for GDM. OGTT has been the cornerstone of GDM diagnosis for decades, however, the preanalytical process of handling OGTT samples needs to be improved. Sample collection, storage and transport during the preanalytical phase are some of the most variable factors which can alter the result. It is therefore important to standardise the preanalytical conditions during an OGTT to avoid misdiagnosis of GDM.
“GDM increases the risk for adverse pregnancy outcomes such as preeclampsia, macrosomia and neonatal hypoglycaemia. However, these outcomes can be improved through self-monitoring blood glucose and managing hyperglycaemia by dietary and lifestyle modifications plus insulin or oral hypoglycaemic agents, if required. Accurate diagnosis therefore is essential; we need to make sure we are not missing any women who need to be treated, likewise, we don’t want to treat women who don’t need to be treated,” said Prof Nolan.
Prof Horvath explains that there are several variables that can impact on the results of an OGTT.
“A major source of error is loss of glucose from blood specimens through glycolysis during the pre-analytical phase. Many Australian sites currently collect and transport OGTT samples at ambient temperature in sodium fluoride (NaF) tubes which is likely to lead to missed diagnosis of GDM in a significant proportion of cases. Unless a blood sample is processed quickly after being taken from the patient, the glucose concentration in the sample will continue to fall. If a sample is put on ice and centrifuged quickly, glycolysis will stop and the glucose level will stay at the original value. However, this is not always a practical solution especially when the OGTT test is done in remote or rural settings that are far away from the laboratory. A potential alternative would be to change the type of blood collection tubes currently used for glucose measurement, to one that prevents glycolysis altogether.”
In June 2017, Prof Nolan and a team of researchers from ACT Pathology, led by Professor Julia Potter, undertook a study[1] to determine the effects of processing time on the rate of GDM diagnosis. By changing the processing time of OGTT blood samples, they showed that a delay in centrifuging blood samples will result in substantially lower rates of diagnosis than if blood is centrifuged early.
“This study, along with a review of the literature[2] led by working party member Emma Jamieson from the University of Western Australia, highlighted the importance of the pre-analytical phase of the total testing process. Something as simple as reducing the time between specimen collection and centrifugation can have a marked impact on patient results and therefore needs to be addressed.
“The literature review revealed that there are other factors to consider in this process, and this is something we aim to work out during the proposed study. By standardising protocols, we will improve diagnosis and as a result, patient outcomes. There are millions of OGTT tests being performed across the world every day, therefore there is a lot of international interest in this. We owe it to all Australian families to get this right,” said Prof Nolan.
