Predicting Diabetes Complications

A new tool can predict the risk of blindness and lower limb amputation among diabetes patients to identify those at high risk of these complications, according to a new prospective cohort study.

Patients with type 1 or type 2 diabetes are at increased risk of blindness and amputation, but they generally do not have accurate assessments of the magnitude of their individual risks.

“The new algorithms calculate the absolute risk of developing these complications over a 10 year period in patients with diabetes, taking account of their individual risk factors,” stated the authors, Julia Hippisley-Cox, professor of clinical epidemiology and general practice, and Carol Coupland, associate professor in medical statistics, at Nottingham University, Nottingham, UK.

The algorithms are based on variables that patients are likely to know or that are routinely recorded in general practice computer systems. “They can be used to identify patients at high risk for prevention or further assessment,” the authors stated, and, therefore, will help personalize care and advice.

Using data derived from electronic patient records in England from 1998-2014, the authors developed the equations from 454,575 patients with diabetes from 763 general practices. Individual risk factors that could influence the results, such as ethnicity, smoking, body mass index, blood pressure, and cholesterol levels, were taken into account.

Mathematical models were then used to calculate separate risk equations for the 10-year risk of blindness and amputation.

In the derivation cohort, 4822 new cases of lower limb amputation and 8063 new cases of blindness occurred during follow-up.

Data from a further 611 general practices were used to validate the two models, which performed well, explaining around 41% and 32% of the variation in time to amputation and blindness, respectively.

“Patients with diabetes tend to overestimate their risk of complications and also overestimate the benefits of treatment,” the authors stated. They cite one study that found patients believed they were highly likely to become blind and to have a lower leg amputation.

“Some people may argue that overestimating the risk of complications might result in patients being more likely to take intensive treatment. However, from a holistic and ethical point of view, more accurate individualised information on the risk of complications may help patients to make more informed decisions about the balance of risks and benefits of treatment options reflecting their own values and choices,” the authors stated.

Overestimating the risk of diabetic complications might increase levels of anxiety and depression, which could negatively affect quality of life. “This is especially important as patients with diabetes are more likely than the general population to experience anxiety and depression,” they stated.

If clinicians could obtain better information on the absolute risk of individual complications, this could also lead to more intensive treatment of modifiable risk factors, such as lowering of HbA1c and tighter blood pressure control. These risk factors are generally considered to reduce the risk of microvascular complications, such as blindness, they noted.

The authors have developed a Web-based calculator to allow clinicians to enter their patients' data to determine the 10-year risk of these complications.

Reference: Hippisley-Cox J, Coupland C. Development and validation of risk prediction equations to estimate future risk of blindness and lower limb amputation in patients with diabetes: cohort study. BMJ 2015;351:h5441.

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