In the long term, continuing monitoring and analysis of a subset of 302 participants from the original Diabetes Prevention Program (DPP) trial of more than 3,000 patients, researchers found detectable retinopathy in 7.6% of patients with prediabetes.

That finding ultimately may warrant both earlier screening for prediabetes and earlier treatment of individuals with recent-onset diabetes. About 13% of participants who had developed diabetes since the start of the DPP outcomes trial were found to have retinopathy.

"These lesions are clearly the same ones we see in type 2 diabetes, but at this point we do not know their meaning or natural history," said DPP vice chair Richard Hamman, MD, DrPH, chair of the department of preventive medicine and biometrics at the University of Colorado School of Medicine in Denver. "This confirms that diabetic retinopathy occurs in prediabetes, but what this means for screening and treatment are questions we cannot really answer yet." The retinopathy study was funded by the National Eye Institute.

Although the lesions that researchers saw were not severe enough to affect vision, the fact that those changes were detectable with targeted photographic testing suggests that "the complications of diabetes may begin years before diagnosis, and much earlier than we thought," said Richard Kahn, PhD, the ADA's chief scientific and medical officer. "'That is really the big news here, because we have not known when the changes start to occur."

In the longitudinal study, patients were evaluated twice yearly for up to five years. Studies involving prediabetes have been few and have been limited in scope, Drs. Kahn and Hamman noted. As such, the retinopathy study's twice annual evaluation of patients provides potentially valuable data that may help researchers determine when the transition from prediabetes to diabetes occurs and the chief clinical reasons the transition is occurring.

The findings are especially important since the clinical diagnosis of diabetes occurs, in some cases, three to five years after onset, Dr. Hamman noted. That might suggest that earlier screening for any sign of prediabetes might yield benefits in prevention — if patients who are at risk and have conditions associated with later development of diabetes can be encouraged to modify contributing lifestyle factors and possibly begin treatment as soon as impaired glucose tolerance is detected.

"What is unique about this is that only a handful of studies have looked at prediabetes — so now we know that we should be looking at patient's eyes as they make this conversion and consider aggressive blood sugar and blood pressure control very early," Dr. Hamman said. "The point is that there is a long time course, and we need to at least be on top of the things that we can control easily." In response to questions from attendees about what the study's findings signal for type 2 diabetes diagnosis threshold levels, Dr. Hamman said further studies involving larger numbers of patients are needed before clinicians and the medical community consider modifying the threshold hemoglobin A1c levels that qualify a patient as having diabetes, since statistically, an estimated 40% of Americans have abnormal blood glucose levels without having diabetes.

Source: Diabetes In Control.com: ADA 65th Annual Scientific Sessions: Late-breaking trials. Presented June 12, 2005.

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