Comparison of differing diagnostic criteria for diabetes: experience from a New Zealand community laboratory

To compare rates of diabetes and impaired glucose tolerance in oral glucose tolerance tests (OGTTs) from a New Zealand community laboratory applying differing diagnostic criteria.

Results from 455 non-pregnant subjects in 75 g oral glucose tolerance tests were reviewed with diabetes assigned according to 1985 WHO criteria (either fasting plasma glucose (FPG) > or =7.8 mmol/L or two-hour glucose > or =11.1 mmol/L), the American Diabetes Association (ADA) criteria (FPG > or =7.0 mmol/L alone), or revised WHO criteria (adopted by the Australasian Working Party) for OGTT (either FPG > or =7.0 mmol/L or 2-h value of > or =11.1 mmol/L). Impaired glucose tolerance (IGT) was assigned according to 1985 WHO criteria (FPG <7.8 mmol/L and 2-h glucose > or =7.8 mmol but <11.1 mmol/L), impaired fasting glucose (IFG) according to the ADA criteria (FPG of > or =6.1 but <7.0 mmol/L), or combination of IFG and IGT (revised WHO criteria).

The 1985 WHO criteria assigned 266 cases (58.5%) as normal glucose tolerance (NGT), 93 (20.4%) as IGT and 96 (21.1%) as diabetic. The ADA fasting criterion assigned 299 (65.7%) as NGT, 82 (18%) as IFG and 74 (16.2%) as diabetic. Only 55 (47.8%) cases identified as diabetic by either criterion met both. Using the combination of FPG > or =7.0 mmol/L or the 2-h glucose of > or =11.1 mmol/L (revised WHO criteria), 115 (25.3%) were assigned as diabetic, 102 (22.4%) as IFG or IGT, and 238 (52.3%) as NGT.

There is thus a 22.9% decrease in diabetes with the ADA fasting criterion, compared with the 1985 WHO criteria. With revised WHO criteria (as adopted by the Australasian Working Party), there is a 19.8% increase in diabetes and a 9.7% increase in those with IFG/IGT. These figures have resource implications for the management of diabetes in New Zealand.