What Is the HLA-B27 Test for Ankylosing Spondylitis?

Ankylosing spondylitis (AS) is the most common type of spondyloarthritis. These are arthritis conditions that affect the spine, sacroiliac (SI) joints, and entheses (the areas where ligaments and tendons attach to bones).

AS is also an autoimmune disease, meaning that the immune system malfunctions and attacks healthy tissues. It causes inflammation that primarily causes pain and stiffness in the spine and SI joints connecting the base of the spine (sacrum) to the pelvis. 

AS is strongly linked to the human leukocyte antigen B27 (HLA-B27) genetic mutation. This mutation is associated with the development of the condition. It might also be related to the disease's severity. HLA genes generally help the immune system recognize and remove foreign invaders like bacteria and viruses. 

The frequency of HLA-B27 in people with AS is 85%. HLA-B27 is also found in people with other types of spondyloarthritis, including psoriatic arthritis (PsA), but the strongest link to HLA-B27 exists with AS.

Having this gene mutation increases your risk for AS, but it is possible to have the gene mutation and never get AS or not have it and still get AS.  

If a healthcare provider suspects you have AS, they might recommend a blood test for HLA-B27. They will make this decision based on your symptoms or the results of other tests. 

This article covers the purpose of HLA-B27 testing, potential risks and contradictions, what to expect before, during, and after the test, results, and more. 

Purpose of Test 

HLA proteins help the immune system distinguish between healthy cells and harmful substances. These proteins are made based on instructions from inherited genes. 

The HLA-B27 test looks for the HLA-B27 protein found on the surface of white blood cells. A healthcare provider will request this test to assess your likelihood of developing an autoimmune disease like AS. They might also use it to confirm a suspected diagnosis of AS. 

Testing will be considered if you have symptoms of AS or another form of spondyloarthritis. Symptoms include inflammation and pain in the spine, hips, or peripheral (large joints), eye inflammation, and severe fatigue.

A healthcare provider might also suspect AS if you are a young adult male because AS is more common under age 40 in people assigned male at birth.

Risks and Contraindications 

The HLA-B27 involves a blood draw in a laboratory or a healthcare provider's office. Risks linked to this test and routine blood draws are minimal.

It is possible to feel discomfort when the needle is inserted and the blood is drawn. Some people might feel pain at the puncture site during the test. 

Blood tests can carry some general risks, but these are rare. These include: 

• Difficulty finding a puncture site, resulting in multiple needle sticks
• Mild pain or bruising where the needle was inserted 
• Excessive bleeding at the needle site
• Fainting or lightheadedness 
• A hematoma—the accumulation of blood under the skin
• Infection at the needle site

You likely will not experience serious problems or side effects from having an HLA-B27 blood test. 

What to Expect

An HLA-B27 test will likely take place once. It might confirm a diagnosis of AS or rule it out. HLA-B27 testing is not definitive, but it adds an extra layer of information to help your healthcare provider reach a diagnosis. 

HLA-B27 testing typically accompanies other tests for autoimmune diseases. Additional testing might include rheumatoid factor, erythrocyte sedimentation rate (ESR), or C-reactive protein (CRP) blood tests. 

Rheumatoid factor is found in the blood of people with rheumatoid arthritis, a type of autoimmune arthritis that attacks the synovial linings of the joints. ESR and CRP tests measure inflammation in the body. 

Before the Test 

The HLA-B27 test requires a standard blood draw. Generally, no special preparation is necessary. 

Your healthcare provider's office, a lab, or a hospital may administer the blood test. Make sure you arrive early to check in, fill out any required forms, show your insurance card, and pay any co-pays or other costs. 

HLA-B27 usually does not require you to fast (abstain from food or drink), but you should check with your healthcare provider to see if you need to stop taking any of your medications before the test. You may also want to avoid strenuous activities before the blood draw, including exercise and heavy lifting.

The technician will usually draw the blood from your arm. Wearing a short-sleeved shirt or a shirt with loose sleeves will make your arm more accessible to them.

During the Test 

The HLA-B27 test is a standard blood draw. A phlebotomist (a healthcare worker trained in drawing blood), lab technician, or nurse performs this.

At the start of the blood test, the nurse or technician will clean your arm in the area where they will draw the blood. They will then tie a rubber band to your upper arm and ask you to make a fist so they can better see the veins. 

The person administering the HLA-B27 test will take a blood sample from a vein inside the elbow or the back of the hand using a small needle. The needle is inserted into the vein, and the blood flows gently through a tube.

When the technician has taken the sample, they remove the needle and rubber band and apply a bandage or clean cotton with medical tape to the needle site. 

You might feel some pain at the puncture site during the test. Let the person administering the blood test know if you feel dizzy or faint, but side effects from routine blood tests are rare. 

After the Test 

When the HLA-B27 is complete, the technician will advise you to put some pressure on the cotton pad or to wear a bandage for a specific time. You should also avoid strenuous activity or heavy lifting for several hours after a blood test to prevent bleeding. 

Apply an ice pack to your arm if you feel stiffness or notice any bruising at the needle site. If stiffness or bruising does not improve or you experience swelling in your arm, reach out to a healthcare provider right away. 

Routine blood tests like HLA-B27 typically do not cause side effects or adverse reactions. Anyone who experiences any worrisome symptoms following blood work should contact a healthcare provider.

Interpreting Results 

About 6% of the U.S. population is positive for HLA-B27 (1 in 17 people). Results from an HLA-B27 test will be negative or positive. Your test results are generally available within a day, but depending on the location of your test, they may take longer. 

A negative test result means HLA-B27 was not found in your blood, though this does not rule out an autoimmune disorder. Your healthcare provider will consider this test result, along with symptoms and additional testing. 

If your HLA-B27 test is positive, HLA-B27 is present in your blood. Though a positive test could cause concern, it does not mean you will go on to have ankylosing spondylitis, psoriatic arthritis, or another autoimmune disease.

To diagnose AS or another autoimmune disorder, a healthcare provider will rely on your symptom history, medical and family history, and the results of other blood work and diagnostic exams (i.e., X-rays and other imaging). 

Follow-Up

If your HLA-B27 is positive and your healthcare provider confirms you have ankylosing spondylitis, you will get a referral to a rheumatologist. A rheumatologist is an internal medicine doctor specializing in musculoskeletal conditions, autoimmune diseases, and inflammatory disorders in people of all ages.

Seeing a rheumatologist is key to managing your AS. They will confirm your diagnosis and get you started on early, aggressive treatment to slow down the disease's progression. Delaying the disease prevents joint and spine damage and other complications, like eye and heart problems. 

Summary 

If a healthcare provider suspects you have ankylosing spondylitis, they will request an HLA-B27 blood test. This blood test looks for HLA-B27 proteins on the surface of white blood cells. HLA-B27 positivity could mean an increased risk for autoimmune diseases like AS, where your immune system malfunctions and starts to attack healthy tissues. 

The HLA-B27 test is a routine blood test that requires no preparation. It typically involves a blood draw from a vein inside the elbow or the back of the hand. 

The results of the HLA-B27 test are either negative or positive. If you test positive and are experiencing symptoms of AS or another autoimmune disease, your healthcare provider will request further testing to confirm a diagnosis. HLA-B27 positivity also occurs in people who do not have autoimmune diseases. 

A Word From Verywell

When you experience symptoms of an autoimmune disease like ankylosing spondylitis, getting a confirmatory diagnosis can take time. Diagnostic testing, including a physical exam, blood work, and imaging, might be necessary. 

With some tests, like blood work, you can walk into a lab for testing and get the results quickly. You must make an appointment and wait longer for the results of other tests, such as magnetic resonance imaging (MRI) or computed tomography (CT). For many people, waiting for results is one of the most stressful parts of the diagnostic process. 

The stress you feel waiting for test results is normal and experienced by many others in the same position. While you wait for answers, find ways to distract yourself. Spend time with loved ones, exercise, or try relaxation activities like yoga, deep breathing, and meditation.

If you find that waiting for answers becomes overwhelming and you are struggling to cope, consider asking your healthcare provider for a referral to a counselor or other mental health provider.