FRAX tool in type 2 diabetic subjects: the use of HbA1c in estimating fracture risk

Abstract

Aims: Patients with type 2 diabetes mellitus (T2DM) have an increased risk of fractures, despite having greater bone mineral density (BMD) than non-diabetic subjects. This has led to the hypothesis that the presence of impaired bone quality among diabetics reduces bone strength. The Fracture Risk Assessment Score (FRAX) algorithm, introduced to facilitate the evaluation of fracture risk, underestimates the risk of fracture in diabetic patients. The purpose of this study is to confirm the relationship between the degree of metabolic compensation and the 10-year probability of a major fracture or a hip osteoporotic fracture observed in our previous study and to ascertain whether glycosylated hemoglobin (HbA1c) can improve the predictive value of FRAX in patients with T2DM. Methods: Our data derive from a retrospective clinical study conducted at the “Tor Vergata” Polyclinic in Rome on 6355 subjects over 50 years of age evaluated for osteoporosis. All available clinical records were examined. HbA1c was available for 242 of these subjects and all had had a Dual-energy X-ray Absorption (DXA) scan of the lumbar spine and femoral neck. The risk of fracture was estimated using the Italian version of the FRAX algorithm. Result: Patients with T2DM had BMD and T-scores higher than those of non-diabetic subjects, while FRAX average values were higher in the non-diabetic group. HbA1c and FRAX are inversely correlated with each other: for each incremental percentage point of HbA1c growth, the FRAX major osteoporotic fracture probability is reduced by 0.915 points and the FRAX hip osteoporotic fracture probability by 1.438 points. The introduction of a correction factor derived from HbA1c, resulted in mean FRAX values of diabetic patients equivalent to those of non-diabetic subjects. Conclusions: We propose a correction factor derived from HbA1c that could enhance the predictive ability of fracture risk estimated by the FRAX algorithm in subjects with T2DM.