A Nomogram Model for Rheumatoid Arthritis-Related Low Muscle Strength was Developed Based on the HALP Score Combined With Clinical Characteristics

Background: Low muscle strength is a common but underrecognized complication of rheumatoid arthritis (RA), associated with functional disability, impaired mobility, reduced quality of life, and adverse health outcomes. This study aimed to identify factors associated with low muscle strength in RA patients and evaluate the incremental value of the hemoglobin, albumin, lymphocyte, and platelet (HALP) score for its identification.Methods: This retrospective multicenter study included patients with RA who were hospitalized in the Departments of Nephrology, Rheumatology and Immunology at Jinhua Hospital of Traditional Chinese Medicine and Lanxi Hospital of Traditional Chinese Medicine between January 2022 and June 2026. Univariate and multivariate logistic regression analyses were performed to identify factors associated with low muscle strength. Multicollinearity among candidate variables was assessed using the variance inflation factor (VIF). To evaluate the incremental value of HALP beyond the clinical-variable selection process, the Clinical Base Model was initially established without including HALP. After the Clinical Base Model was finalized, HALP was added as a single additional variable to construct the nested Base + HALP Model. The incremental discriminative performance of the HALP score was evaluated by comparing changes in the area under the receiver operating characteristic curve (ΔAUC), integrated discrimination improvement (IDI), and net reclassification improvement (NRI). Decision curve analysis (DCA) was performed to assess the estimated net benefit of each model across a range of risk thresholds. Internal validation was conducted using bootstrap resampling, and sensitivity analysis was performed among patients aged ≥50 years using the same analytical procedures.Results: A total of 220 patients with RA were included, of whom 81 (36.8%) had low muscle strength. Compared with patients without low muscle strength, those with low muscle strength were older, had lower body mass index (BMI) and HALP scores, higher erythrocyte sedimentation rate disease activity score (DAS28-ESR) values, and were more likely to be female. Multivariate logistic regression analysis identified age, sex, BMI, DAS28-ESR, current glucocorticoid (GC) use, and HALP score as independent factors associated with low muscle strength. The clinical base model demonstrated an apparent AUC of 0.784 (95% confidence interval (CI), 0.722–0.847). After the addition of the HALP score, the AUC increased to 0.829 (95% CI, 0.775–0.883), with a ΔAUC of 0.045 (DeLong test, p = 0.020). The Base + HALP model also demonstrated improved classification performance, with an NRI of 0.663 (95% CI, 0.402–0.924; p = 0.001) and an IDI of 0.072 (95% CI, 0.039–0.107; p = 0.002). After 1000-bootstrap internal validation, the AUCs of the clinical base and Base + HALP model were 0.766 (95% CI, 0.707–0.826) and 0.809 (95% CI, 0.757–0.863), respectively. Decision curve analysis demonstrated that the Base + HALP model provided a greater estimated net benefit than the clinical base model and the treat-all and treat-none strategies, particularly across threshold probabilities from approximately 10% to 60%.Conclusions: The HALP score, age, sex, BMI, DAS28-ESR and current GC use were independently associated with low muscle strength in patients with RA. The Base + HALP Model demonstrated good discrimination, calibration and estimated net benefit. However, further independent external validation and prospective studies are still needed in the future to clarify the role of this model.