Is There a Test for Ankylosing Spondylitis? Here's How Doctors Diagnose This Spinal Condition

Back pain can be debilitating, so it makes sense to try to find the root cause. Ankylosing spondylitis (AS) is just one possible diagnosis, and a rare one at that, affecting less than 1% of the population, per Johns Hopkins Medicine.

But if there's any reason to suspect AS, your doctor will likely refer you to a rheumatologist for further evaluation. At that point, there are a few key steps to figuring out whether you have the condition.

Is there a test for ankylosing spondylitis?

There are three main assessments that help a doctor determine if your symptoms are the result of ankylosing spondylitis.

"Ankylosing spondylitis is diagnosed by clinical examination, radiographic findings, and also the serum marker HLA-B27," says Nick Shamie, MD, chief of orthopedic spine surgery and professor of orthopedic surgery and neurosurgery at UCLA School of Medicine.

In other words, it's a combination of what your doctor can see, and what you say, when you're in the exam room; what an X-ray or MRI shows; and what a specific blood test reveals.

One test by itself isn't enough to qualify for ankylosing spondylitis, Dr. Shamie tells Health. Your doctor will be looking for evidence both in the examination (like pain or stiffness) along with evidence from an imaging test, like inflammation of the sacroiliac joints (which connect the pelvis and lower spine) or fusion of vertebrae.

Patient history and physical exam

When you visit your doctor, expect to answer questions about how long you've been feeling pain or stiffness in your back. The point is to determine whether it's a chronic problem, which is typically "for more than three months," Dr. Shamie says. Your doctor may also ask you about what you've tried to treat your back pain in the past and how well it's worked, and if you have any other symptoms that concern you.

Next, your doctor will test the range of motion in your spine by having you bend and twist in different directions, as well as watch you take a breath to check that your is able to fully expand. In advanced cases, ankylosing spondylitis can fuse the spine in such a way that the ribs aren't able to move well during inhalation. And that make it more difficult for you do breathe, says the UK-based National Axial Spondyloarthritis Society.

Last, your doctor may press on or move areas that typically cause you pain to see if they can recreate it.

Imaging tests

An X-ray is typically the main imaging test a doctor orders when they suspect ankylosing spondylitis. An X-ray gives your doctor a picture of your spine to see if there are any changes occurring—specifically, it can help them understand whether bones have begun to fuse along the spine, per Dr. Shamie.

But early cases of ankylosing spondylitis may not show up in the bones, in which case, a doctor may also order an MRI. The MRI can identify areas of inflammation along the spine joints, which can be an early indicator of ankylosing spondylitis, says Dr. Shamie.

Lab tests

There is no one lab test that can determine whether or not a patient has ankylosing spondylitis, and your doctor may order several different tests to get a better understanding of what's causing your pain.

Some common tests for inflammation include C-reactive protein (CRP) and erythrocyte sedimentation rate (ESR)—aka your "SED" rate, says the Spondylitis Association of America.

There is one blood test specifically associated with ankylosing spondylitis, called HLA-B27. This test evaluates whether you have a specific protein on your white blood cells. A positive test result can't tell you whether you have ankylosing spondylitis—it just tells you that you have the protein, which may increase your disease risk, according to the Cleveland Clinic. Along with physical symptoms, a positive HLA-B27 test can be helpful in firming up a diagnosis, says the US National Library of Medicine. But a positive test alone doesn't mean have you have ankylosing spondylitis.

In fact, its significance varies by race and ethnicity, notes the Spondylitis Association of America. Most white people with ankylosing spondylitis—about 95%—test positive for HLA-B27. Among people with AS from Mediterranean counties, 80% test positive; among African-Americans with AS, only 50% are HLA-B27-positive.

What to expect after your diagnosis

The first goal for new patients is to get their pain under control. This is usually accomplished with prescription-strength non-steroidal anti-inflammatory drugs (NSAIDs), such as ibuprofen, naproxen, or indomethacin, per the Spondylitis Association of America. (And when those first-line treatments aren't enough, other types of medicines for reducing pain and swelling and controlling inflammation may be prescribed.)

Next, your doctor will want to understand how well and how safely you're able to move. "We want to prevent a fall or a high-velocity injury because the spine in ankylosing spondylitis is not forgiving," Anand Veeravagu, MD, assistant professor of neurosurgery and director of minimally invasive neurospine surgery at Stanford Medicine, tells Health.

From there, it's about keeping you up and moving. "We think about how to slow down some of the pain associated with ankylosing spondylitis and prevent areas that are mobile from being overworked," says Dr. Veeravagu.

That often means physical therapy, which can help strengthen muscles that support the spine, pelvis, and lower body, as well as help with balance. It may also include learning some new ways of moving that avoid painful and stiff areas of the body, notes Dr. Veeravagu.