Plasma glucose reference interval in a low-risk population. 2. Impact of the new WHO and ADA recommendations on the diagnosis of diabetes mellitus

The aim of the study was to establish a reference interval of fasting venou s plasma glucose (FPG) from healthy individuals. A prospective modified cro ss-sectional population-based study was made with random selection of 2100 persons in age-stratified groups greater than or equal to 18 years identifi ed from the local Personal Identification Register. The invitation was acce pted by 755 persons, of which 726 aged 18-92 years were eligible. They did not have a diabetes diagnosis, were non-pregnant and capable of fasting for 8 h. All participants filled in a questionnaire on medical risk factors. B lood for the FPG and haemoglobin A1c (HbA1c) measurements was drawn in acco rdance with a standardized procedure. A total of 302 participants carried d iabetes risk indicators and were ruled out. The FPG concentrations in the r emaining low-risk population (n=424) was In Gaussian distributed. The FPG 9 7.50 centile in this group was 6.4 mmol/L (95% CI: 6.3-6.5 mmol/L), in cont rast to the WHO and ADA theoretical limit of 6.1 mmol/L. Their diagnostic d ecision limit of 7.0 mmol/L FPG corresponded to the 99.86 centile of the FP G reference distribution (95% CI: 6.8-7.1). Subclassification of the refere nce population showed increasing FPG with increasing BMI and age and was hi gher in men than in women. The study determined the FPG 95% interfractile r eference interval in a healthy population. The interval in glucose concentr ation between the 97.5 centile of the reference interval and the ADA-WHO di agnostic limit is very narrow. The clinical application of the diagnostic d iscriminator and the interpretation of the WHO-ADA grey zone from 6.1 to 7. 0 mmol/L FPG may consequently be biased because of poorly defined limits an d influence from BMI, age and gender.