Molecular and Serologic Detection of HLA-B27 among Ankylosing Spondylitis Patients with Some Clinical Correlations

Abstract

ABSTRACT:BACKGROUND: HLA-B27 can effect clinical presentation and course of ankylosing spondylitis. Different detection techniques of HLA-B27 are available with variable sensitivities and specificities. OBJECTIVE: To compare serologic and molecular diagnostic techniques of detecting HLA-B27 status and to correlate it with some clinical variables among ankylosing spondylitis patients.PATIENTS AND METHODS: A cross-sectional study was conducted on 83 Iraqi patients with ankylosing spondylitis. Clinical and laboratory evaluations were reported. HLA-B27 status was determined in all patients by real-time PCR using HLA-B27 RealFast™ kit; ELISA method was used as well to detect soluble serum HLA-B27 antigens using Human Leukocyte Antigen® kit. RESULTS: The mean age of patients ± SD was (38.4±9.8) years. Male to female ratio was 9:1. Disease onset occurred <30 years in 78% of cases. All (100%) cases had lower back pain, 44 (54%) patients had enthesitis, 14 (16.9%) had peripheral arthritis, 12 (14.5%) had eye involvement, while cardiovascular disease and psoriasis were present in one patient (1.2%) each. HLA-B27 was detected in 55 (66.3%) patients by real-time PCR. The disease onset was earlier and disease duration was longer in HLA-B27-positive patients (p-value<0.05 for both). Uveitis was significantly associated with HLA-B27 positivity (p=0.032). HLA-B27 positive cases by ELISA test were 32 (38.6%) patients. Comparing HLA-B27 gene detection by real-time PCR with sHLA-B27 detection by ELISA revealed that the sensitivity of ELISA was 38.18%, specificity was 60.71% and positive predictive value (PPV) was 61.8%.HLA-B27 typing by microlymphocytotoxicity (MLCT) test from initial old serologic typing was available for a subgroup of 28 (33.7%) cases. Comparison of ELISA and MLCT results with real-time PCR in this subgroup of 28 cases revealed that ELISA method showed a sensitivity of 60.6%, specificity of 72.72% and PPV of 86.95%, while MLCT showed a sensitivity of 68.96%, specificity of 80%, and PPV of 90.9% CONCLUSION: Real-time PCR detection of HLA-B27 status is superior to serological techniques (ELISA and MLCT) as the latter two yielded high false results, with MLCT being relatively better than ELISA.