Ankylosing spondylitis (AS) is a common, highly heritable inflammatory arthritis affecting primarily the spine and pelvis and affects approximatively 0.5% of the population. Accumulating evidence has demonstrated that human leukocyte antigen (HLA) class I molecule B27 (HLA-B27) is strongly associated to AS : >90% of AS patients are HLA-B27 positive. Over 100 different allelic variants of B27 have been recognized (HLA-B2701 to HLA-B27106) in AS patients, among which B27*05 and B27*02 are widely prevalent in European populations, and B27*04 is predominant in Asian populations. The lamp human HLA-B27 tag detection kit detects the SNP rs4349859, which tags for the European most AS associated subtypes B*2702 and B*2705. This SNP does not tag for African or Asian subtypes. A large genome-wide association study demonstrated that a tag-single-nucleotide polymorphism (SNP) can be used to determine HLA-B*27 status. It was shown that one single nucleotide polymorphism (SNP), rs4349859, had a strong ability to tag HLA-B27 in European patients from Australia and Great Britain. This SNP has a very high negative predictive value and a high positive predictive value : - 99% of Specificity (True negative) - 98% of Sensitivity (True positive) It is important to note that the HLA-B27 test is not a diagnostic test for ankylosing spondylitis. Also, the association between AS and HLA-B27 varies among different ethnic and racial groups. It can be a very strong indicator in that more than 95 percent of people in the Caucasian population who have AS test positive for HLA-B27. However, close to 80 percent of AS patients from Mediterranean countries and only 50 percent of African American patients with AS are HLA-B27 positive.