# Lupus nephritis and U1-RNP-antibodies are associated with low bone mineral density and osteoporosis in patients with systemic lupus erythematosus: baseline findings in a sub-cohort of patients with inflammatory rheumatic diseases

## TL;DR

This study finds that lupus patients with certain disease features, like lupus nephritis and specific antibodies, are more likely to have low bone density and osteoporosis.

## Contribution

The study identifies lupus nephritis classes III and IV, U1-RNP antibodies, and high C-reactive protein as novel risk factors for osteoporosis in SLE patients.

## Key findings

- 35% of SLE patients had lupus nephritis, with classes IV and V being most common among those with osteoporosis.
- 3D-DXA femur parameters showed potential in identifying past fragility fractures.
- Clinical remission and higher BMI were positively associated with better bone mineral density.

## Abstract

Patients with systemic lupus erythematosus (SLE) are at higher risk for osteoporosis and fragility fractures. Our study aimed to identify disease-specific factors with impact on bone mineral density (BMD) and the risk of osteoporosis, and to evaluate the effectiveness of DXA-derived 3D femur parameters versus BMD and trabecular bone score (TBS) in discriminating pre-existent fragility fractures.

We analyzed baseline data of a consecutive subcohort of patients with SLE with current or past GC treatment, fulfilling the EULAR/ACR 2019 SLE classification criteria. We used multivariable linear and logistic regression models to identify BMD- and osteoporosis-related factors. DXA-derived 3D measurements of the femur were performed with 3D-Shaper software. Discriminatory performance of BMD, TBS and 3D femoral parameters for fragility fractures was assessed by AUC values.

Forty-one percent of 110 patients with SLE had osteoporosis. Lupus nephritis (LN) was present in 35% of cases, with 61% (23/38) of these being predominantly classified as classes IV and V. Factors significantly associated with lower BMD included LN classes III and IV, U1-RNP antibodies, higher C-reactive protein, and longer disease duration. Clinical remission, higher Siglec-1 levels, higher body mass index, and higher health assessment questionnaire (HAQ) scores correlated positively with BMD. Osteoporosis was linked to LN, higher age, HAQ, and complement factor 3 levels. Our findings suggest that 3D bone structure analysis may be helpful in discriminating past vertebral fractures.

Disease severity indicated by LN, high CRP, presence of U1-RNP antibodies, and extended disease duration are detrimental to bone health. Moreover, 3D-DXA parameters can be integrated in clinical practise to assess bone health.

The online version contains supplementary material available at 10.1186/s13075-025-03610-y.

SLE patients have lower bone mineral density and higher fracture risk than healthy individuals, but the impact of disease-specific risk factors is unclear.

SLE patients have lower bone mineral density and higher fracture risk than healthy individuals, but the impact of disease-specific risk factors is unclear.

Identifies lupus nephritis (classes III and IV), C-reactive protein, and U1-RNP antibodies to be associated with an increased risk of osteoporosis, while clinical remission appears to benefit bone health.Proposes that bone structural parameters as measured by 3D-DXA can be used to discriminate past fragility fractures.

Identifies lupus nephritis (classes III and IV), C-reactive protein, and U1-RNP antibodies to be associated with an increased risk of osteoporosis, while clinical remission appears to benefit bone health.

Proposes that bone structural parameters as measured by 3D-DXA can be used to discriminate past fragility fractures.

Underlines the importance of DXA screening for patients with SLE, especially in those with high disease activity and longer duration of the disease.Suggests that new methods for assessing bone structure could help in providing better fracture risk assessments.

Underlines the importance of DXA screening for patients with SLE, especially in those with high disease activity and longer duration of the disease.

Suggests that new methods for assessing bone structure could help in providing better fracture risk assessments.

The online version contains supplementary material available at 10.1186/s13075-025-03610-y.