Retinopathy study challenges current approach to diabetes diagnosis

A joint Australian-American study has found there is no distinct glycaemic threshold for the onset of retinopathy, further challenging the concept that diabetes can be defined simply by a blood sugar result. The study used multiple retinal photographs of each eye from about 11,000 participants in the Blue Mountains Eye Study and AusDiab, and the Multi-Ethnic Study of Atherosclerosis in six American Communities. The overall prevalence of retinopathy was 11.5%. “However, we found inconsistent evidence of a uniform glycaemic threshold for prevalent and incident retinopathy, with analyses suggesting a continuous relationship,” the researchers said. The fasting blood glucose level of 7.0 mmol/L, widely used to diagnose diabetes, had a sensitivity of only 40% for detecting retinopathy, with a specificity ranging from 81% to 96%. The 7.0 mmol/L criterion for diagnosis was based on three studies in the 1990s that suggested a clear glycaemic threshold separating people at high and low risk of diabetic microvascular complications, especially retinopathy. However, the studies were limited by an incomplete and imprecise ascertainment of retinopathy: one used direct clinical ophthalmoscopic examination, and the others used a single retinal photograph. Findings from this latest study had a number of implications. The first was that retinopathy was much more common than previously thought, although not all cases were necessarily a result of elevated blood glucose levels. The second was that retinopathy was more like other diabetic microvascular and macrovascular complications than previously thought, having a continuous, graded relationship with blood glucose. “These findings suggest that the criteria for diagnosing diabetes could need reassessment,” the researchers concluded. An editorial commented that the study raised more questions than it answered. The retinal lesions detected in people with ‘normal’ glucose levels were not always predictive of future diabetes, and there were wide racial variations within the American participants. The current 7.0 mmol/L threshold did seem reasonably effective at distinguishing people with a substantially higher risk of diabetes-related harm, and the study did not propose any alternative diagnostic criteria. The findings re-emphasised the need to comprehensively assess risk factors rather than relying on a single laboratory result, the editorial said. Reference...