FRAX fracture risk in women with a recent fracture of the distal forearm: agreement between assessments with and without bone mineral density and impact of measurement side in the individual patient

The Fracture Risk Assessment Tool (FRAX) has been developed by the World Health Organization to evaluate the 10-year risk of a hip fracture and a major osteoporotic fracture. We examined the agreement between fracture risk calculated with and without femoral neck bone mineral density (BMD) in individual patients and the impact of BMD measurement side. Bilateral femoral neck BMD results obtained by dual-energy X-ray absorptiometry and clinical risk factor data from 140 women (age 66 +/- 8 years) with a recent distal forearm fracture were used for FRAX analyses. Discrepancies between pairs of risk assessments were analysed by the Bland-Altman method. Agreement on the individual level was expressed as 95 % limits of agreement (LoA) and on the group level as the mean (or median) of intra-individual differences (the bias). The femoral neck T-score was -1.69 +/- 0.87 (hip with lowest BMD value). The risk of a major fracture and a hip fracture based on the lowest femoral neck BMD value was 23.8 +/- 21.4 % and 7.6 +/- 8.3 %, respectively. For major fracture risk assessed without versus with the lowest BMD value, lower and upper LoA were -12.3 and 21.1 percentage points (pp) (bias 4.4 pp, p < 0.0001). The corresponding LoA for hip fracture risk were -11.6 and18.6 pp (bias 3.5 pp, p < 0.0001). LoA for major fracture risk assessed with the lowest versus the highest BMD value were 0.0 and 9.5 pp (bias 2.0, p < 0.0001), and correspondingly for hip fracture risk 0.0 and 9.5 pp (bias 1.0 pp, p < 0.0001). Intra-individual differences increased with increasing fracture risk. In conclusion, the 10-year fracture risk calculated without BMD was on the average slightly overestimated compared to calculations with BMD. On the individual patient level differences between fracture risk assessments with and without BMD were pronounced. The side of BMD measurement may also significantly influence the risk assessment result in individual patients.