Human leukocyte antigen B27 (HLA-B27) is found in varying degrees all throughout the world. For a study, researchers sought to determine the prevalence of HLA-B27 in an Argentinian cohort with axial spondyloarthritis (axSpA), to compare HLA-B27–positive and HLA-B27–negative individuals, and assess its effectiveness as a diagnostic biomarker. An observational study of individuals over the age of 18 with axSpA diagnosed in a fast track program was conducted (Reuma-Check SpA). Blood tests, HLA-B27, sacroiliac imaging, and ultrasound for enthesitis were performed on all patients. In addition, sociodemographic information and SpA symptoms were gathered. The clinical assessor was not aware of any other investigations that were being conducted. Patients with persistent low back pain without axSpA who did the same circuit in the same period were utilized as controls for the sensitivity and specificity study and were paired 1:1. (sex & age). 

There were 150 patients in all, 75 of whom had axSpA and 75 of whom did not. HLA-B27 was found in 43% of people (95% CI, 30–53). Age of start of low back pain (36 vs 46 years), BASFI (Bath Ankylosing Spondylitis Functional Index) (4 vs 5), and extra-articular SpA characteristics such as uveitis and inflammatory bowel disease were shown to be different between HLA-B27–positive and HLA-B27–negative individuals (29% vs 50% ). When comparing this frequency (low back pain control group), the difference was 43% versus 9% (odds ratio, 7.7; 95% CI, 2.8–24), and HLA-B27 had a sensitivity of 43%, specificity of 91%, the positive predictive value of 85%, the negative predictive value of 58%, and likelihood ratio of 4.9 (95% CI, 3–8). HLA-B27 was found in 43% of patients with axSpA; positive individuals had an earlier age of onset (36), a higher BASFI, and more SpA characteristics. HLA-B27 has high specificity but low sensitivity for SpA diagnosis.