Lab result explainedInflammationLast updated November 11, 2026

HLA-B27 test: what a positive or negative result means for ankylosing spondylitis, uveitis and back pain

HLA-B27 (HLA-B27) · HLA-B27 typing (ordered alone or with CRP and ESR in a back-pain or uveitis work-up) · reported in Reported as positive (present) or negative (absent); no numeric value or units

HLA-B27 is a version of a gene that shapes a protein on the surface of almost all your cells, and the HLA-B27 test tells you whether you carry it. It is not a measure of inflammation and it does not go up or down; the result is simply positive (present) or negative (absent) and stays that way for life. About 6 to 8 percent of people of European ancestry carry HLA-B27, roughly 1 to 4 percent of people of African, East Asian or Hispanic ancestry, and the great majority of carriers never develop any related illness.

The test matters because HLA-B27 is strongly linked to a family of inflammatory conditions called spondyloarthritis. Around 90 percent of people of European ancestry with ankylosing spondylitis are positive, as are 50 to 80 percent of people with reactive arthritis, about half of those with acute anterior uveitis (sudden inflammation inside the front of the eye) and a smaller share of those with psoriatic or inflammatory-bowel-disease arthritis. In someone with months of inflammatory back pain that started before age 45, a positive result makes an inflammatory cause roughly nine times more likely.

What the test cannot do is diagnose anything on its own. Because only about 1 to 5 percent of HLA-B27 carriers ever develop ankylosing spondylitis, a positive result in a person with ordinary mechanical back pain is far more likely to be a coincidence than a diagnosis. Equally, a negative result does not rule spondyloarthritis out: 5 to 10 percent of white patients and up to half of Black patients with ankylosing spondylitis are HLA-B27 negative. The result is always read with your symptoms, examination, inflammatory markers and imaging.

HLA-B27 at a glance

What it is: a genetic test for one variant of the HLA-B gene; reported as positive or negative, never high or low.
How common: positive in about 6 to 8 percent of people of European descent (about 6 percent of US adults overall), 2 to 4 percent of Black Americans, and under 1 percent of some East Asian populations.
Positive: raises the chance of ankylosing spondylitis, non-radiographic axial spondyloarthritis, reactive arthritis, acute anterior uveitis and psoriatic or IBD-related spondylitis, but does not diagnose any of them.
Negative: makes ankylosing spondylitis less likely but does not exclude it; 5 to 10 percent of white patients and 40 to 50 percent of Black patients with the disease are negative.
Lifetime risk of ankylosing spondylitis for a positive person with no family history is about 1 to 5 percent; with an affected first-degree relative it is about 15 to 20 percent.
Next step: a positive result with inflammatory back pain, uveitis, heel pain or asymmetric joint swelling usually leads to CRP, ESR and MRI of the sacroiliac joints and a rheumatology referral.

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What HLA-B27 measures

HLA stands for human leukocyte antigen. The HLA genes on chromosome 6 code for proteins that sit on cell surfaces and present fragments of proteins to T cells, which is how the immune system inspects cells for infection. HLA-B is one of the class I genes, and B27 is one of its many variants (alleles). Everyone inherits two copies of HLA-B, one from each parent; a positive test means at least one copy is B27. Carrying two copies is rare and may slightly increase disease risk but is not usually reported.

Most US laboratories test by flow cytometry, which uses a fluorescent antibody to detect the B27 protein on white cells, or by PCR, which detects the gene itself. Flow cytometry is fast but the antibody can cross-react with HLA-B7 and a few related alleles, so an equivocal or weakly positive flow result is usually confirmed by PCR. There are more than 100 B27 subtypes; B*27:05 (the common Western subtype), B*27:02 and B*27:04 carry disease risk, while B*27:06 (Southeast Asia) and B*27:09 (Sardinia) do not appear to. Routine reports do not list the subtype unless specifically requested.

Why B27 predisposes to spondyloarthritis is still debated. Leading theories are that the B27 protein misfolds and stresses the cell, that it forms unusual pairs on the cell surface that activate immune cells, and that it presents particular microbial or self peptides in a way that triggers joint and eye inflammation. Gut bacteria appear to be involved; most people with ankylosing spondylitis have microscopic bowel inflammation even without bowel symptoms.

Normal range for HLA-B27

Reference ranges vary between labs and by age, sex and pregnancy. Use the range printed on your own report.

Group	Typical range (Reported as positive (present) or negative (absent); no numeric value or units)	Notes
Negative	HLA-B27 not detected	The expected result for 92 to 94 percent of people of European ancestry and 96 to 99 percent of people of African or East Asian ancestry.
Positive	HLA-B27 detected	A genetic trait, not a disease. Most positive people stay well. Interpretation depends entirely on symptoms.
Equivocal or indeterminate (flow cytometry)	Weak fluorescence, often from cross-reacting HLA-B7	Usually resolved by a PCR-based test; ask whether a confirmatory method was used.
Positive in ankylosing spondylitis	About 90 percent of white patients; 50 to 60 percent of Black patients	A negative result therefore reduces but does not remove the possibility.
Positive in acute anterior uveitis	About 50 percent	B27-associated uveitis is typically sudden, painful, one eye at a time, and recurrent.
Positive in reactive arthritis	50 to 80 percent	Arthritis 1 to 4 weeks after a gut or genital infection (Chlamydia, Salmonella, Shigella, Campylobacter, Yersinia).
Positive in psoriatic or IBD-associated spondylitis	About 40 to 60 percent with spinal involvement; 15 to 25 percent with peripheral arthritis only	Lower than in ankylosing spondylitis.
Population prevalence	About 6 percent of US adults overall (NHANES 2009); up to 15 to 25 percent in northern Scandinavia and some indigenous populations	Labs do not set a reference range; prevalence is given for context.

Positive HLA-B27

A positive HLA-B27 means you carry a genetic variant that raises your susceptibility to spondyloarthritis. How much that matters depends on why the test was ordered. If you have chronic low back pain that began before age 45, came on gradually, is worse in the second half of the night and in the morning, and improves with movement rather than rest, a positive result makes axial spondyloarthritis considerably more likely and is one of the criteria used to classify it. Under the ASAS classification criteria, HLA-B27 plus two other features of spondyloarthritis (such as heel enthesitis, uveitis, psoriasis, inflammatory bowel disease, dactylitis, a good response to NSAIDs, a family history or a raised CRP) is enough to classify axial spondyloarthritis even when imaging is normal.

If you have no such symptoms, a positive result is a finding, not a diagnosis. The absolute lifetime risk of ankylosing spondylitis in a B27-positive person picked at random is around 1 to 5 percent; it rises to roughly 15 to 20 percent if a parent or sibling has the disease. Most positive people are never affected, and no monitoring is needed in the absence of symptoms. The practical value of knowing is that new inflammatory back pain, a red painful eye with light sensitivity, or a swollen heel or finger should be reported promptly rather than waited out.

A positive result in someone with a sudden red, painful, light-sensitive eye points to HLA-B27-associated acute anterior uveitis, which accounts for about half of all acute anterior uveitis. Roughly 30 to 40 percent of people with ankylosing spondylitis have at least one attack of uveitis, and in some people the eye attack is the first sign that leads to the spinal diagnosis. Each attack needs same-week treatment by an eye specialist to prevent scarring and glaucoma.

Common causes

Inherited from a parent
HLA-B27 is passed down in the usual way: each child of a carrier has a 50 percent chance of inheriting it. It is not caused by anything you did, cannot be acquired, and does not change over time.
Ankylosing spondylitis (radiographic axial spondyloarthritis)
Chronic inflammation of the sacroiliac joints and spine with eventual visible change on X-ray. About 90 percent of white patients are positive. Typical onset is between 17 and 45, with more men than women among those who reach the radiographic stage.
Non-radiographic axial spondyloarthritis
The same disease process before X-ray changes appear, diagnosed by MRI or by HLA-B27 plus clinical features. Positive in about 70 to 80 percent; men and women are affected equally and about 10 to 40 percent progress to radiographic disease over 10 years.
Acute anterior uveitis
Inflammation of the iris and ciliary body, with sudden eye pain, redness, light sensitivity and blurred vision, usually in one eye and recurring on either side. Half of cases are B27-associated, and about half of those will turn out to have an underlying spondyloarthritis.
Reactive arthritis
Asymmetric arthritis of the knees, ankles or feet, sometimes with conjunctivitis, urethritis or skin changes, developing 1 to 4 weeks after a gut infection or chlamydia. 50 to 80 percent are positive, and positive patients have longer and more severe courses.
Psoriatic arthritis with spinal involvement
About 20 to 30 percent of people with psoriasis develop arthritis; when it involves the spine or sacroiliac joints, 40 to 60 percent are B27 positive, compared with about 20 percent when only the fingers and toes are involved.
Arthritis associated with Crohn's disease or ulcerative colitis
Around 10 to 20 percent of people with IBD develop spondyloarthritis. Those with spinal involvement are B27 positive in 50 to 70 percent of cases; peripheral joint involvement is less strongly linked.
Juvenile spondyloarthritis (enthesitis-related arthritis)
Hip, knee and heel inflammation in children, more often boys over 6. HLA-B27 is part of the classification criteria and positive in 60 to 80 percent.
False positive on flow cytometry
The antibody used in flow cytometry can bind HLA-B7 and related alleles, producing a weak or equivocal positive in a person who is truly negative. PCR-based typing resolves this.

Symptoms that can go with it

None in most carriers; HLA-B27 itself causes no symptoms
Low back or buttock pain lasting over 3 months, starting before age 45, worse at night and in the morning, easing with activity
Morning stiffness in the back lasting longer than 30 minutes
Heel pain at the Achilles tendon or sole (enthesitis), or a whole swollen finger or toe (dactylitis)
A red, painful, light-sensitive eye with blurred vision, often one side at a time (acute anterior uveitis)
Asymmetric swelling of a knee, ankle or foot, sometimes after a bout of diarrhea or a genital infection
Fatigue, chest wall pain with deep breathing, and over years, reduced spinal flexibility

Negative HLA-B27

A negative HLA-B27 is the expected result for more than 9 in 10 people and means you do not carry the variant. If the test was ordered for back pain, a negative result makes axial spondyloarthritis less likely (the negative likelihood ratio is about 0.1) but it does not exclude it. In white populations about 5 to 10 percent of people with ankylosing spondylitis are HLA-B27 negative; in Black populations it is 40 to 50 percent, and in non-radiographic axial spondyloarthritis roughly a quarter of patients are negative. Negative patients tend to be diagnosed later, partly because the result wrongly reassures.

If your back pain has the features of inflammatory back pain and your CRP is raised, or you have psoriasis, inflammatory bowel disease, uveitis or a family history of spondyloarthritis, a negative HLA-B27 should not end the work-up. MRI of the sacroiliac joints is the test that detects early inflammation regardless of HLA status, and a rheumatologist can classify axial spondyloarthritis on imaging alone. HLA-B27-negative spondyloarthritis is treated in exactly the same way as positive disease.

Common causes

The normal result
92 to 94 percent of people of European ancestry and 96 to 99 percent of people of African or East Asian ancestry do not carry HLA-B27. In most people tested, a negative result simply means the back pain has a mechanical or other non-inflammatory cause.
HLA-B27-negative ankylosing spondylitis
Other genes (ERAP1, IL23R and several other HLA-B alleles such as B*07, B*40 and B*15) and non-genetic factors contribute. Negative patients have the same spinal disease but less uveitis, later diagnosis and a weaker family clustering.
Non-radiographic axial spondyloarthritis
About 20 to 30 percent of people with inflammation on sacroiliac MRI but normal X-rays are B27 negative; the ASAS imaging arm allows classification on MRI plus one clinical feature without HLA-B27.
Psoriatic arthritis or IBD-associated arthritis
These are B27 negative in the majority of peripheral cases and in a sizeable minority of spinal cases, so a negative result carries little weight when psoriasis or IBD is present.
Mechanical back pain, disc disease or fibromyalgia
The common causes of back pain in people under 45 are not related to HLA-B27 at all. A negative result in someone without inflammatory features points back toward these explanations.
A non-disease-associated subtype
Rarely, a person carries B*27:06 or B*27:09, which flow cytometry reports as positive but which carry little or no risk; conversely, laboratories using subtype-specific PCR may report these as negative. This is uncommon outside Southeast Asia and Sardinia.

Symptoms that can go with it

None; a negative result causes nothing
Persisting inflammatory back pain, uveitis or heel enthesitis despite a negative result still needs imaging and specialist assessment

Read it alongside

CRP — raised in about 40 to 60 percent of people with active axial spondyloarthritis; a raised CRP with a positive HLA-B27 strengthens the case and predicts response to biologic treatment.
ESR — a second inflammation marker; often raised in active disease but normal in many patients, so a normal value does not exclude it.
Complete blood count and hemoglobin — mild anemia of chronic disease accompanies long-standing inflammation; the CBC also screens for other causes of pain and fatigue.
Rheumatoid factor and anti-CCP — characteristically negative in spondyloarthritis (which is why it is called seronegative); positivity points toward rheumatoid arthritis instead.
Fecal calprotectin — raised in many people with spondyloarthritis who have subclinical gut inflammation; a high value prompts evaluation for Crohn's disease or ulcerative colitis.
Urine or genital chlamydia test and stool culture — when reactive arthritis is suspected, identifying the triggering infection guides treatment.
MRI of the sacroiliac joints — not a blood test, but the investigation that most often settles the question in a B27-positive person with inflammatory back pain.

What usually happens next

If you are positive and have inflammatory back pain, enthesitis, uveitis or a family history, expect a rheumatology referral with CRP, ESR and an MRI of the sacroiliac joints; X-rays are also taken but can be normal for years.
If you are positive and have no symptoms, no follow-up testing is needed; the useful action is to know the warning symptoms (night-time back pain and stiffness, a red painful eye, heel pain, a swollen digit) and report them early.
If you are negative but your symptoms fit inflammatory back pain, ask whether MRI is still appropriate; HLA-B27-negative spondyloarthritis is common enough that a negative result should not close the question.
Anyone with a B27-associated uveitis attack should be told the result, because an eye specialist will want to know, and any future red painful eye needs same-day attention.
Tell your clinician if the lab used flow cytometry and the result was reported as weak or equivocal; a PCR-based confirmation is straightforward.
Ask about screening for associated conditions when relevant: psoriasis, inflammatory bowel symptoms and, in long-standing disease, bone density and cardiovascular risk.

Diet, lifestyle and natural levers with evidence

What can move HLA-B27 once the cause is known. Nothing here replaces finding the cause.

Nothing changes the result itself

Strong evidence

HLA-B27 is inherited and fixed; no diet, supplement, herb or lifestyle change makes a positive person negative or alters the chance of a given test being positive. The levers that matter are the ones that reduce disease activity and progression in people who have developed spondyloarthritis, and they are listed below. The test can be done at any time, fasting or not, and is unaffected by medication, infection or inflammation.

Regular exercise and a structured physiotherapy program

Strong evidence

Exercise is the cornerstone of non-drug management in ankylosing spondylitis. A Cochrane review of 11 trials found that supervised group physiotherapy and home exercise improved spinal mobility, physical function (about 1.3 points better on the 10-point BASFI scale) and patient-rated wellbeing compared with no intervention, and that supervised programs outperformed home exercise alone. The 2019 ACR/SAA/SPARTAN guideline strongly recommends regular physical activity and physical therapy for all patients.

People with advanced spinal fusion or osteoporosis should avoid high-impact and spinal-manipulation therapies; chiropractic manipulation of a fused spine has caused fractures.

Stopping smoking

Strong evidence

Smoking is the lifestyle factor most consistently linked to worse outcomes. A systematic review and meta-analysis of 29 studies found smokers with axial spondyloarthritis had higher disease activity, worse function, more MRI inflammation and faster radiographic progression of the spine than non-smokers, and smoking also blunts the response to TNF inhibitors. Quitting is the one lifestyle change with evidence for slowing structural damage.

Omega-3 fatty acids

Preliminary evidence

A small Swedish randomized trial in 24 people with ankylosing spondylitis found that a high dose of omega-3 (4.55 g a day of EPA plus DHA) for 21 weeks lowered disease activity on the BASDAI score, while a low dose (1.95 g) did not. Evidence in spondyloarthritis specifically is thin, but omega-3 has broader anti-inflammatory evidence in rheumatoid arthritis, where meta-analyses show reduced joint pain and NSAID use at doses of 2.7 g a day or more.

High doses increase bleeding tendency and, in some cardiovascular trials, atrial fibrillation; discuss if you take anticoagulants or NSAIDs.

Gut-directed measures: fiber, Mediterranean-style eating and treating bowel inflammation

Preliminary evidence

Up to 60 percent of people with spondyloarthritis have microscopic gut inflammation, and gut bacteria are thought to help trigger B27-associated disease. Small studies report lower disease activity with Mediterranean-style diets, and treating coexisting inflammatory bowel disease improves joint symptoms. A low-starch diet popularized for ankylosing spondylitis has only uncontrolled, decades-old evidence and is not recommended by any guideline.

Restrictive diets risk weight loss and nutrient deficiency; discuss any major dietary change with your clinician or a dietitian.

When to see a clinician promptly

A sudden red, painful eye with light sensitivity and blurred vision: possible acute anterior uveitis, which needs same-day assessment by an eye specialist to prevent permanent damage.
Back or neck pain after even a minor fall or bump in someone with long-standing ankylosing spondylitis: a fused spine fractures easily and the fracture can injure the spinal cord; this is an emergency.
Back pain that wakes you in the second half of the night, lasts more than 3 months and started before age 45, especially with morning stiffness over 30 minutes.
A hot, swollen knee or ankle, a swollen whole finger or toe, or heel pain that does not settle, particularly within a month of a gut or genital infection.
New chest pain, breathlessness or palpitations in someone with ankylosing spondylitis, which can affect the heart valves and conduction system.
Numbness, weakness or bladder or bowel difficulty with back pain, which needs urgent assessment regardless of HLA-B27 status.

Frequently asked questions

What does HLA-B27 positive mean?

It means you carry one particular variant of the HLA-B gene, as do about 6 to 8 percent of people of European ancestry. It is a genetic trait, not a diagnosis. It raises your susceptibility to ankylosing spondylitis, reactive arthritis, acute anterior uveitis and related conditions, but most carriers never develop any of them; the lifetime risk of ankylosing spondylitis for a positive person without a family history is roughly 1 to 5 percent. Whether the result matters depends on whether you have symptoms.

Can you have ankylosing spondylitis and be HLA-B27 negative?

Yes. About 5 to 10 percent of white patients and 40 to 50 percent of Black patients with ankylosing spondylitis are HLA-B27 negative, and about a quarter of people with non-radiographic axial spondyloarthritis are negative. A negative result lowers the probability but never rules the diagnosis out. If you have inflammatory-type back pain, a raised CRP, psoriasis, inflammatory bowel disease or uveitis, an MRI of the sacroiliac joints is the next step whatever your HLA-B27 result.

What is the connection between HLA-B27 and uveitis?

HLA-B27 is the single strongest genetic risk factor for acute anterior uveitis, a sudden painful inflammation of the iris. About half of all cases are B27-associated; these attacks typically affect one eye at a time, alternate between eyes over the years and respond well to prompt steroid eye drops. About half of people with B27 uveitis have or will develop a spondyloarthritis, so an ophthalmologist who finds B27 uveitis will often ask about back pain and refer to rheumatology.

What are the chances of passing HLA-B27 to my children?

Each child has a 50 percent chance of inheriting the variant if one parent carries it, and a 75 percent chance if both do. Inheriting the gene is not the same as inheriting the disease: a child of a parent with ankylosing spondylitis who is B27 positive has roughly a 15 to 20 percent chance of developing it, and a B27-negative child has a much lower risk. Testing children without symptoms is not generally recommended, because a positive result cannot be acted on and may cause unnecessary worry.

Is HLA-B27 a type of arthritis or an autoimmune disease?

Neither. It is a normal variant of an immune-system gene found in millions of healthy people. The diseases linked to it (spondyloarthritis, uveitis, reactive arthritis) are inflammatory conditions that sit between classic autoimmunity and autoinflammation. People sometimes say they have HLA-B27 as shorthand for having a B27-associated disease, but the gene itself is not an illness and does not need treatment.

Does HLA-B27 cause back pain?

Not directly. The gene increases the chance of developing inflammation in the sacroiliac joints and spine, which causes a distinctive pattern of back pain: gradual onset before age 45, worse with rest and at night, better with movement, with prolonged morning stiffness. Ordinary mechanical back pain, which is far more common, is unrelated to HLA-B27, so a positive test in someone with activity-related pain that eases with rest does not explain the pain.

Do I need to fast or stop medication for an HLA-B27 test?

No. It is a genetic test on white blood cells and the result is the same at any time of day, with or without food, and regardless of medications, infections or flares. It never needs repeating once done by a reliable method, although an equivocal flow cytometry result is sometimes repeated by PCR to be sure.

What other tests are done if HLA-B27 is positive?

If you have symptoms, the usual additions are CRP and ESR to measure inflammation, a complete blood count, and an MRI of the sacroiliac joints (and sometimes the spine), which can show inflammation years before X-rays change. Depending on the picture, your clinician may add tests for psoriasis, inflammatory bowel disease (fecal calprotectin), a triggering infection (chlamydia, stool culture) and an eye examination. If you have no symptoms, no further testing is needed.

References

HLA-B27 antigen. MedlinePlus Medical Encyclopedia, US National Library of Medicine (2024)
Reveille JD, Hirsch R, Dillon CF, Carroll MD, Weisman MH. The prevalence of HLA-B27 in the US: data from the US National Health and Nutrition Examination Survey, 2009. Arthritis and Rheumatism (2012)
Rudwaleit M, van der Heijde D, Landewé R, et al.. The development of Assessment of SpondyloArthritis international Society classification criteria for axial spondyloarthritis (part II): validation and final selection. Annals of the Rheumatic Diseases (2009)
Sieper J, Poddubnyy D. Axial spondyloarthritis. The Lancet (2017)
Braun J, Sieper J. Ankylosing spondylitis. The Lancet (2007)
Ward MM, Deodhar A, Gensler LS, et al.. 2019 update of the American College of Rheumatology/Spondylitis Association of America/Spondyloarthritis Research and Treatment Network recommendations for the treatment of ankylosing spondylitis and nonradiographic axial spondyloarthritis. Arthritis Care and Research (2019)
Wakefield D, Clarke D, McCluskey P. HLA-B27 anterior uveitis: immunology and immunopathology. Ocular Immunology and Inflammation (2016)
Dagfinrud H, Kvien TK, Hagen KB. Physiotherapy interventions for ankylosing spondylitis. Cochrane Database of Systematic Reviews (2008)
Villaverde-García V, Cobo-Ibáñez T, Candelas-Rodríguez G, et al.. The effect of smoking on clinical and structural damage in patients with axial spondyloarthritis: a systematic literature review. Seminars in Arthritis and Rheumatism (2017)
Sundström B, Stålnacke K, Hagfors L, Johansson G. Supplementation of omega-3 fatty acids in patients with ankylosing spondylitis. Scandinavian Journal of Rheumatology (2006)
Ankylosing spondylitis. Merck Manual Professional Version (2024)
Khan MA. Update on the genetic epidemiology of HLA-B27 and ankylosing spondylitis. Current Opinion in Rheumatology (2017)

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This page is educational and is not medical advice or a diagnosis. Lab results have to be interpreted together with your history, symptoms and other results by a clinician who knows you. Do not start or stop a supplement to change a lab value before the cause is known.