Traditional clinical risk factors outperform disease activity and hematologic indices for FRAX hip fracture risk in rheumatoid arthritis.

BACKGROUND

Hip fractures are among the most devastating complications of osteoporosis, yet determinants of the Fracture Risk Assessment Tool (FRAX)-estimated 10-year hip fracture probability (FRAX-Hip) in rheumatoid arthritis (RA) remain incompletely defined. The incremental value of RA disease activity and complete blood count (CBC)-derived inflammatory indices beyond traditional FRAX clinical risk factors is uncertain.

OBJECTIVES

To identify determinants of 10-year FRAX-Hip risk in RA and to compare the predictive performance and incremental value of RA disease activity indices and CBC-derived inflammatory markers.

METHODS

In a cross-sectional cohort of 248 RA patients undergoing dual-energy X-ray absorptiometry, we calculated femoral neck bone mineral density (BMD)-adjusted FRAX-Hip and defined high risk as FRAX-Hip ≥3%. Determinants were assessed using Firth penalized logistic regression and multivariable linear regression, and incremental value was evaluated using changes in area under the receiver operating characteristic curve (AUC), net reclassification improvement (NRI), and integrated discrimination improvement (IDI).

RESULTS

High FRAX-Hip risk was mainly driven by older age, female sex, lower body mass index, glucocorticoid exposure, and lower femoral neck BMD. Among disease activity measures, the Simplified Disease Activity Index (SDAI) provided the largest-yet modest-incremental improvement over a base clinical model (ΔAUC = 0.013; NRI = 0.903; IDI = 0.075). In contrast, CBC-derived inflammatory indices showed poor discrimination (AUC 0.46-0.62) and negligible incremental value. The clinical model explained >93% of the variance in log-transformed FRAX-Hip.

CONCLUSIONS

Traditional FRAX clinical factors dominate FRAX-Hip risk estimation in RA. SDAI adds only modest incremental value, whereas CBC-derived indices do not improve risk stratification. FRAX with BMD remains a robust tool for identifying high-risk patients, underscoring the importance of optimizing age-, glucocorticoid-, and bone density-related risk factors while maintaining tight RA disease control.