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Glossary

HLA-B27

A gene marker found on a blood test. It's common in people with spondyloarthritis and it's also common in people with nothing wrong. So it moves the odds rather than settling anything.

One test result gets treated as a verdict, and it isn't one. What it's worth depends heavily on where your family came from, which is not something most people are told when the blood is drawn. That's the whole of this page, and the rest is the evidence for it.

Quick answerHLA-B27 is a gene marker rather than a diagnosis, and an ordinary blood test is all it takes to find it. It turns up in the ill and the healthy alike. In one study in Lebanon, 41.1 percent of patients with axial spondyloarthritis had it, and so did 3.8 percent of blood donors.
How useful the test is depends on where your family came from, and the range is wide. One study of people with ankylosing spondylitis found the marker in 85.3 percent of White patients, 86.7 percent of Latino patients, and 62.5 percent of Black patients. One Moroccan group had 136 people with the disease and just 7 of them tested positive. So a negative result means one thing in one place and something else in another, and a doctor who knows that reads your test differently.

What this test is

HLA-B27 is one form of a gene, and the gene family it belongs to has a job worth knowing about. It helps your immune system tell your own cells from things that don't belong there. Everybody has genes in that family, and this particular form turns up more often in people with spondyloarthritis than in people without.

An ordinary blood test finds it, which is part of why it gets ordered so readily. Here is the part that trips almost everybody up at first. Having this form is fairly common and developing one of these diseases is not, and putting those two facts together is what shows you why a result on its own settles very little.

What a positive result is worth

A positive result moves the odds without closing the question, and that difference is the whole of this page. One study in Lebanon typed 141 patients with axial spondyloarthritis alongside 106 blood donors. The marker was found in 41.1 percent of the patients and in 3.8 percent of the donors, so as a test it cleared 96.2 percent of the donors and a positive came with a likelihood ratio of 10.9.

A likelihood ratio of 10.9 is a genuine move and it isn't a verdict. It takes whatever chance your doctor started with and raises it. If that starting chance was low, a positive result leaves it moderate rather than certain, which is a different result than most people imagine.

Having it without being ill

Most people with the marker never develop a rheumatic disease, and one study puts a number on what that costs them. The answer turns out to be nothing at all. It looked at 407480 UK Biobank participants of European ancestry, and having the marker made no difference to death rate, at a hazard ratio of 1 with the true value from 0.97 to 1.1 and a P value of 0.349.

No rise in deaths from blood vessel disease appeared either. That paper does report a raised death rate elsewhere, and it's worth keeping the two apart. People with established ankylosing spondylitis had a standardized mortality ratio of 1.37, from 1.11 to 1.62, and that belongs to having the disease rather than to the marker itself.

One more finding from that paper is worth knowing about. Some people with axial spondyloarthritis have no damage showing on x-ray. Their death rate came in below the general population, at 0.44 from 0.23 to 0.77, which is not a result anybody expected.

It isn't the only gene involved

This marker is the famous one and it isn't the whole picture. Several genes are involved in these diseases and this happens to be the one with a name people recognize. One study built a score from many genes at once and set it against the single marker.

For the job of telling ankylosing spondylitis from healthy controls, the many-gene score reached 0.924 while the marker on its own reached 0.869. Sacroiliac scanning reached 0.885 and C-reactive protein reached 0.700. So the marker holds its own without leading the field, which is a fair summary of where it ranks.

The predictive figures make the difference concrete, so start from a one-in-ten chance. That's roughly where somebody under 45 with long-term back pain is before any test is ordered. From there the many-gene score reached a positive predictive value of 78.2 percent and a negative predictive value of 100 percent, while the single marker managed 51.9 percent and 97.9 percent.

A separate study followed 1075 patients and found two other markers in this gene family turning up slightly more often in one group. That group had joint swelling outside the spine as well. Both links were marginal and neither one is in routine use, so you won't be tested for them.

What differs between positives and negatives

One large study typed 2269 people with axial spondyloarthritis across 24 countries, of whom 1753 had the marker and 516 did not. The two groups looked different in ways worth knowing about. Those with the marker were more often men, at 72.1 percent against 54.3 percent, and they had a family history more often, at 29.8 percent against 15.3 percent. They were diagnosed younger too, at a mean of 31.6 years against 37.7 years.

Those without it more often had features outside the spine. Joint swelling elsewhere appeared in 47.5 percent against 42.1 percent, and psoriasis in 19.4 percent against 10.2 percent. Tender tendon attachments were 56.6 against 49.8 percent, and bowel disease was 12.8 against 3.4. The bowel figure is the one that is notable from that list, because it is at nearly four times the rate of the positives, and it's the clearest hint that the two groups don't line up neatly.

That doesn't change what you're offered in the clinic. It does mean one thing worth holding onto. Somebody who tests negative may have a slightly different-looking illness rather than no illness at all.

Common misconceptions.

Myth. A positive result means I have the disease.

Reality. It doesn't, and most people who have this marker never develop a rheumatic disease at all. What a positive does is raise the odds, and in one study it came with a likelihood ratio of 10.9, which is a real move. Raising the odds and settling a question are two different things, and your symptoms, your exam, and your scans still do most of the work.

Myth. A negative result rules it out.

Reality. Far from it, and the numbers make that plain. In one study of 141 patients with axial spondyloarthritis, only 41.1 percent had the marker, and its negative predictive value was 55.13 percent. In one Moroccan group of 136 patients, just 7 tested positive, so a negative result leaves the question open and how far open depends on where your family came from.

Myth. Everyone with ankylosing spondylitis has it.

Reality. Most do and not all, which is a distinction worth holding. One study of 925 people with the disease found it in 85.3 percent of White patients and 86.7 percent of Latino patients, while among Black patients it was 62.5 percent. A second study split people by x-ray damage and found 82 percent among those with damage against 68 percent among those without, at a P value of 0.03.

Myth. Having it will shorten my life.

Reality. Not on the evidence here, and the study behind that is a large one. It looked at 407480 UK Biobank participants of European ancestry, and having the marker made no difference to death rate at all, at a hazard ratio of 1 from 0.97 to 1.1. The raised death rate in that paper belonged to people with established disease rather than to people who simply have the marker.

Myth. It's the only genetic thing that counts.

Reality. It's the best known one and it isn't the whole story. One study built a score from many genes at once, and that score told ankylosing spondylitis from healthy controls at 0.924, against 0.869 for this marker alone. A separate study found two other markers turning up more often in people who also had joint swelling outside the spine.

Related terms.

References.

  1. Ziade N; Abi Karam G; Merheb G et al. HLA-B27 prevalence in axial spondyloarthritis patients and in blood donors in a Lebanese population: Results from a nationwide study. Int J Rheum Dis. 2019;22:708-714. 10.1111/1756-185X.13487Nationwide study in Lebanon
  2. Jamalyaria F; Ward MM; Assassi S et al. Ethnicity and disease severity in ankylosing spondylitis a cross-sectional analysis of three ethnic groups. Clin Rheumatol. 2017;36:2359-2364. 10.1007/s10067-017-3767-6Cross-sectional analysis of 925 patients with ankylosing spondylitis enrolled in a longitudinal outcomes cohort
  3. Li Z; Khan MK; van der Linden SM et al. HLA-B27, axial spondyloarthritis and survival. Ann Rheum Dis. 2023;82:1558-1567. 10.1136/ard-2023-224434Two linked analyses
  4. Li Z; Wu X; Leo PJ et al. Polygenic Risk Scores have high diagnostic capacity in ankylosing spondylitis. Ann Rheum Dis. 2021;80:1168-1174. 10.1136/annrheumdis-2020-219446Development and validation of polygenic risk scores in people of European and East Asian ancestry
  5. Chaudhary H; López-Medina C; Khan MA et al. Clinical profile and treatment utilisation based on HLA-B*27 status in axial spondyloarthritis: results from ASAS-PerSpA study. RMD Open. 2023;9. 10.1136/rmdopen-2023-003179Journal Article
  6. Essouiri J; Abourazzak FE; Kona I et al. Profile of Patients with Spondyloarthritis in Morocco. Curr Rheumatol Rev. 2018;14:258-263. 10.2174/1573397113666170406125338Retrospective observational study in one Moroccan rheumatology department analysing the records of 136 patients diagnosed with spondyloarthritis between January 2009 and June 2014
  7. Hong C; Kwan YH; Leung YY et al. Comparison of ankylosing spondylitis and non-radiographic axial spondyloarthritis in a multi-ethnic Asian population of Singapore. Int J Rheum Dis. 2019;22:1506-1511. 10.1111/1756-185X.13603Comparative study of 262 patients with axial spondyloarthritis in a Singapore registry
  8. Frantz C; Portier A; Etcheto A et al. Acute anterior uveitis in spondyloarthritis: a monocentric study of 301 patients. Clin Exp Rheumatol. 2019;37:26-31. PMID 30620268Cross-sectional single-centre observational study
  9. Naovarat BS; Gensler L; Ward M et al. Associations of sociodemographic, clinical factors and HLA-B alleles with enthesitis and peripheral arthritis in patients with ankylosing spondylitis. RMD Open. 2025;11. 10.1136/rmdopen-2024-004589Multicentre longitudinal observational cohort of 1075 patients with ankylosing spondylitis from the Prospective Study of Outcomes in Ankylosing Spondylitis

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This page gathers the published research on this subject into one place. The studies behind it were published between 1989 and 2026, and every figure links to the paper it came from. Those studies were peer reviewed. This summary of them was not. Dr. Sarah Luebker is reviewing these pages one at a time and has not reached this one yet, so it carries no medical review date and nothing here is her opinion or her advice to you. Each page gets updated as she reaches it. It is here in the meantime because the science is worth having in one organized place that is easy to find and easy to read. Talk to your own clinician before acting on any of it.