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New tools calculate absolute risk for blindness, amputation in adults with diabetes
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Two new algorithms can accurately calculate the absolute risk during a 10-year period for developing blindness or needing limb amputation, two potentially serious complications for men and women living with type 1 or type 2 diabetes, according to research in The BMJ.
In a prospective cohort study of database information collected for more than 450,000 patients with diabetes, Julia Hippisley-Cox, PhD, and Carol Coupland, BSc, MSc, PhD, both professors at the University of Nottingham, United Kingdom, said the tools — similar to the QRISK2 algorithm to predict cardiovascular risk — are based on variables that patients are either likely to know or are recorded routinely in general practice visits.
“Patients with type 1 or type 2 diabetes are at increased risk for blindness and amputation, but generally do not have an accurate assessment of the magnitude of their individual risk,” Hippisley-Cox told Endocrine Today. “There are currently no tools available to calculate risk for other complications, such as amputation or blindness. This is important since these are the complications which patients with diabetes fear most and which most impair quality of life.”
Hippisley-Cox and Coupland analysed electronic medical records from 454,575 patients aged 25 to 84 years with type 1 or type 2 diabetes in the United Kingdom between 1998 and 2014, using the QResearch and Clinical Practice Research Datalink databases. The researchers randomly allocated 763 of the general practices involved to the derivation dataset; 254 general practices were allocated to a validation dataset. The researchers determined patient entry date; patients were entered at the earliest date of diagnosis for either blindness, limb amputation or death.
The researchers examined predictor variables, including age at cohort entry, type of diabetes and number of years since diagnosis, smoking status, ethnic group, HbA1c, BMI, systolic blood pressure, treated hypertension and CVD, and used established methods to develop risk prediction equations for both limb amputation and blindness (separate equations were derived for men and women).
The final model for lower limb amputation in women included age, systolic BP, HbA1c, deprivation, duration of diabetes, smoking status, ethnicity, rheumatoid arthritis, congestive cardiac failure, peripheral vascular disease and chronic renal disease. For men, the final model included the additional variables of diabetes type and atrial fibrillation. BMI and the serum cholesterol/HDL cholesterol ratio were not significantly associated with risk for limb amputation in men or women, the researchers wrote.
For blindness, the final models in men and women included age, cholesterol/HDL cholesterol ratio, systolic BP, HbA1c, 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 for blindness.
“Pre-existing proliferative retinopathy or maculopathy was the strongest risk factor [for blindness], with a 2.7-fold increase for women and a 2.9-fold increase for men,” Hippisley-Cox and Coupland wrote.
The tools, Hippisley-Cox said, are intended to better inform screening and treatment decisions.
“[Blindness and amputation] are also the complications for which patients are most likely to overestimate their risk and overestimate the benefits of intensive treatment,” Hippisley-Cox told Endocrine Today. “This new tool provides a way for patients and doctors to calculate their chances of having these complications based on their profile.” – by Regina Schaffer
Disclosure: Hippisley-Cox is the co-director of QResearch, a nonprofit organization and leading commercial supplier of IT for general practices in the U.K., and reports serving as a paid director of ClinRisk Ltd, which produces open- and closed-source clinical software. Coupland reports serving as a paid consultant statistician for ClinRisk Ltd.
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