National survey on the execution of the oral glucose tolerance test (OGTT)

The aim of the present survey was to evaluate the adherence of Italian laboratories to the internationally accepted guidelines in carrying out the OGTT for the diagnosis of diabetes in the general population and for the screening of gestational diabetes mellitus (GDM). A questionnaire was designed to investigate issues related to the OGTT and sent to 400 specialists in laboratory medicine working in public or private laboratories nationwide. Only 50% of the laboratories performed the OGTT according to protocols defined in agreement with local reference diabetes centres. OGTT using 75 g of glucose in adults and 1.75 g/kg for children, as recommended by WHO, was performed by 87.1% of the laboratories. WHO indications to collect samples at baseline and at 120 min were followed by 33.2% of the centres. Higher variability was highlighted with respect to the methodology for GDM screening: 49.8% of the laboratories always adopted the twostep procedure consisting of a glucose challenge test and subsequent OGTT in positive cases; 4.9% performed the 100-g OGTT with four blood samples; 1.6% the 75-g OGTT with two blood samples; and 2.7% the 75-g OGTT with four blood samples. Relevant variability was highlighted for performance of the OGTT in general and GDM screening in particular. A variable relationship between laboratories and diabetes centres was also detected, which might represent a relevant indicator for the rationalisation and standardisation of the method for performing an OGTT.