Background/Purpose: Inflammatory back pain (IBP) is a hallmark symptom of axial spondyloarthritis (axSpA) and is frequently used as a clinical entry point for further evaluation, including HLA-B27 testing and inflammatory marker assessment. However, the specificity of IBP for identifying individuals with immunogenetic or biochemical features of axSpA in the general population remains uncertain.

Methods: We analyzed data from the 2009–2010 cycle of the National Health and Nutrition Examination Survey (NHANES), a cross-sectional, nationally representative dataset. IBP was defined using Calin, ESSG, Berlin 7b, and Berlin 8a criteria, based on self-reported responses to the NHANES Arthritis Questionnaire. HLA-B27 typing and high-sensitivity CRP (hsCRP) were measured in a subset of 2,320 participants aged 20–69. We conducted logistic regression models adjusting for age, sex, race/ethnicity, smoking, alcohol use, diabetes, and hypertension. Causal mediation analysis was performed to assess whether CRP levels mediated any relationship between HLA-B27 and IBP.

Results: Among 746 participants with complete data, the prevalence of HLA-B27 was 6.1%. IBP prevalence ranged from 5.0% to 6.0% depending on the criteria used. In fully adjusted models, HLA-B27 positivity was not significantly associated with IBP by any of the criteria (e.g., Berlin 8a: OR 0.88 [95% CI 0.13–5.98], p=0.876) (Figure 1). Similarly, CRP levels were not associated with IBP (e.g., Berlin 8a: OR 0.94 [95% CI 0.63–1.39], p=0.694) (Figure 2). Mediation analysis showed no significant indirect effect of CRP on the HLA-B27–IBP relationship (indirect effect OR ≈ 1.00, p > 0.6 across all models) (Figure 3).

Conclusion: In a nationally representative U.S. sample, IBP as defined by established criteria was not associated with either HLA-B27 positivity or CRP levels. These findings suggest that IBP symptoms alone may have limited utility for identifying individuals with immunogenetic or inflammatory features of axSpA in the general population. Future strategies for early recognition of axSpA may require multimodal approaches that integrate clinical, laboratory, and imaging data beyond symptom-based screening alone.

Figure 1. HLA-B27 association with Inflammatory Back Pain Criteria adjusted OR for age, sex, race, smoking, DM, HTN.

Figure 2. CRP association with Inflammatory Back Pain Criteria adjusted OR for age, sex, race, smoking, DM, HTN.

Figure 3. Causal Mediation Analyses for IBP. HLA-B27 association with IBP was not signficant after adjustment (natural direct effect). CRP does not mediate the association as well (natural Indirect effect).

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ACR Meeting Abstracts - https://acrabstracts.org/abstract/inflammatory-back-pain-is-not-associated-with-hla-b27-positivity-or-crp-levels-in-a-nationally-representative-u-s-population/