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Equation Predicts Diabetes-Related Amputation, Vision Loss Risk

Patients with type 1 or type 2 diabetes are at increased risk of amputation and vision loss but generally do not have accurate assessments of the magnitude of their individual risks. Researchers from the United Kingdom have developed an equation that calculates the absolute risk of developing these complications over a ten-year period, taking into account the patients’ individual risk factors. They said it can be used to identify patients with diabetes in need of further assessment. The web calculator that implements the risk equations for the final models can be found at qdiabetes.org/amputation-blindness/index.php. Further research is needed, however, to evaluate the clinical outcomes and cost-effectiveness of using these risk equations in primary care.

Study: To develop the web calculator, a cohort study was conducted to derive and validate the risk equations in a large population of patients with diabetes; an external validation was also completed. The researchers examined the following predictor variables based on established risk factors for vascular disease: age at cohort entry, type of diabetes, number of years since diagnosis of diabetes, smoking status, ethnic group, Townsend deprivation score, glycated hemoglobin (HbA1c mmol/mol, continuous), systolic blood pressure, body mass index (BMI), total serum cholesterol/high-density lipoprotein cholesterol ratio, atrial fibrillation, congestive cardiac failure, cardiovascular disease, treated hypertension, peripheral vascular disease, chronic renal disease, rheumatoid arthritis, and proliferative retinopathy or maculopathy. Hazards models were used to derive separate risk equations for blindness and amputation in men and women that could be evaluated at ten years.

Lower-limb amputation: The final model for lower-limb amputation in women included age, systolic blood pressure, HbA1c, deprivation, duration of diabetes, smoking status, ethnicity, rheumatoid arthritis, congestive cardiac failure, peripheral vascular disease, and chronic renal disease. The final model in men also included type of diabetes and atrial fibrillation. BMI and the serum cholesterol/high-density lipoprotein cholesterol ratio were not significantly associated with risk in men or women. Increasing duration of diabetes was associated with an increased risk of lower-limb amputation in men and women. Increasing levels of smoking were associated with an increased risk of amputation; the association was more marked in women than in men. For heavy smokers compared with non-smokers, a 1.9-fold increase in risk of amputation was seen for women and a 1.3-fold increased risk for men. South Asian ethnic groups had a lower risk compared with people whose ethnic group was either white or not recorded; Caribbean and black African men also had lower risks. Preexisting peripheral vascular disease was associated with the highest risks (fourfold in women and threefold in men), followed by chronic renal disease (2.7-fold in women and 2.3-fold in men).

Vision loss: The final models for vision loss in men and women included age, cholesterol/high-density lipoprotein cholesterol ratio, systolic blood pressure, HbA1c, deprivation, duration of diabetes, type of diabetes, chronic renal disease, and existing proliferative retinopathy or maculopathy. BMI and smoking status were not significantly associated with risk. Increasing values of age, HbA1c, and systolic blood pressure were associated with an increased risk of vision loss, as were increasing values of the serum cholesterol/high-density lipoprotein cholesterol ratios. Increasing duration of diabetes was associated with increased risk despite adjustment for age and other risk factors. There was a significant interaction between renal disease and age. Preexisting proliferative retinopathy or maculopathy was the strongest risk factor, with a 2.7-fold increase for women and a 2.9-fold increase for men.

The study, “Development and Validation of Risk Prediction Equations to Estimate Future Risk of Blindness and Lower Limb Amputation in Patients With Diabetes: Cohort Study,” was published November 11 in The BMJ.

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