Background: Several estimates of the risk of progression to diabetes in people with impaired fasting glucose (IFG) or impaired glucose tolerance (IGT) have been reported.

Objective: To provide an estimate of the risk of progression to diabetes and regression to normoglycemia in these populations.

Design: Systematic overview and meta-analysis of prospective cohort studies published from 1979 until 2004.

Setting: Global cohort studies.

Patients: People with IFG or IGT detected by a screening oral glucose tolerance test.

Measurements: Fasting and post-load plasma glucose levels.

Results: The absolute annual incidence of diabetes in individuals with various categories of IFG or IGT varied from 5 to 10%. Compared to normoglycemic people the meta-analyzed relative risk and 95% confidence interval for diabetes was: 6.35 (4.87-7.82) in people with IGT; 5.52 (3.13-7.91) in people with isolated IGT; 4.66 (2.47-6.85) in people with IFG; 7.54 (4.63-10.45) in people with isolated IFG; and 12.13 (4.27-20.00) in people with both IFG and IGT. People with IGT were 0.33 times as likely to be normoglycemic after 1 year compared to people with normal glucose tolerance (95% CI 0.23-0.43).

Limitations: Studies that used differing criteria for IFG and IGT were included, and participants were classified on the basis of only one test.

Conclusion: IFG and IGT are associated with similar, high relative risk for incident diabetes. The combined abnormality of IFG plus IGT is associated with the highest relative risk.