Background/Purpose:

In 2015, the Canadian Rheumatology Association published their Choosing Wisely recommendations regarding HLA-B27 testing.  One of the criteria that triggers testing is inflammatory back pain in patients < 45 years old (y/o). This was chosen based on ASAS criteria for axial and peripheral SpA which were validated in patients under 45 y/o. However, studies have indicated that 3-10.6% of patients with SpA diagnosis occur in patients >= 45 y/o, hinting at a “late onset” SpA group. We sought to assess the utility of HLA-B27 testing in patients >= 45 y/o to determine how many were eventually diagnosed with SpA.

Methods:

Retrospective analysis of all patients >= 45 y/o who had HLA-B27 testing by a non-rheumatology provider (PCP, Ophthalmology, Orthopedics) at Regions Hospital/ Health Partners, a large academic vertically and horizontally integrated health care system, from 1/1/2014 – 7/1/2015. Chart review identified features of SpA (defined as inflammatory back pain > 3 months with onset < 45 y/o, peripheral synovitis, enthesitis, dactylitis, psoriasis, or uveitis) that were present at the time of HLA-B27 testing. We assessed if imaging (Xray, CT, or MRI) identifying sacroiliitis +/- 6 months from HLA-B27 order was present, the presence of inflammatory markers (ESR or CRP) +/- 1 month from the HLA-B27 order, and if an eventual diagnosis of SpA was made. Data were analyzed to generate descriptive information regarding frequency, and logistic regression was used to identify which features of SpA and SpA subsets are identified in HLA-B27 tested patients >= 45 y/o.

Results:

Over the 18 months, 291 HLA-B27 tests were ordered by non-rheumatologists. The age ranged from 1 to 92 years. 141/291 tests were in individuals >= 45 y/o [63 tests > 50 y/o, 44 tests > 55 y/o]. Diagnosis of a SpA was made in 11/141 (7.8%) (8 AS, 3 PsA) whereas 32 total diagnoses of SpA were made in the entire group (regardless of age). Thus, 11/32 (34.4%) of SpA diagnosis occurred in patients >=45 y/o.  At a 95% confidence level, psoriasis (OR 14.66) and back pain (OR 13.98) were the significant predictors for SpA in the group >=45 y/o (Table 1). There were insufficient numbers to evaluate the predictive value of the other symptoms in the group >=45 y/o. In the entire group, back pain was also the most significant predictive factor (OR 28.5) for a diagnosis of SpA. Thus inflammatory back pain can trigger evaluation for SpA regardless of age.

Conclusion:

In this study, of the 291 non-rheumatologist ordered HLA-B27 tests, 11/141 (7.8%) of patients >=45 y/o eventually received a SpA diagnosis which represents 1/3 of the eventual SpA diagnoses. This significant amount of late onset SpA combined with the highest OR being back pain emphasizes the importance of being aware of late onset SpA as well as considering inflammatory back pain regardless of age as a feature for SpA.  

Table 1. Demographics, HLA-B27 results, SpA diagnoses and features in a large integrated healthcare system.