Ankylosing Spondylitis -Is HLA-B27 essential for diagnosis?

Back pain is one of the most common complaints in the physician’s office.  A test like HLA- B27 gets frequently checked by physicians. If the test comes back positive, many patients get concerned about an inflammatory disease of the back, called ankylosing spondylitis. Can HLA-B27 make the diagnoses of Ankylosing spondylitis? In this article,I will discuss:

  • What is HLA-B27?

  • What is the meaning of HLA-B27 positive? 

  • Is HLA-B27 essential for a diagnosis of ankylosing spondylitis?

What is HLA-B27? 

HLA stands for “Human leukocyte antigens”. These are a collection of genes located on chromosome 6 that encodes for molecules involved in the immune system function. Most of the HLA genes express their products on the surface of white blood cells. White blood cells are important components of our immune system and they are involved in fighting infections. Some HLA genes are expressed on all nucleated cells. 

There are 2 classes of HLA genes:

  • Class I (HLA-A, B, and C). These HLA-Class I antigens are expressed on almost all cells of the body, except a few cell types like red blood cells.
  • Class II (HLA-DP, DQ, and DR). These HLA-Class II molecules are expressed on antigen-presenting cells (like dendritic cells, macrophages, or B cells). These are the cells of our immune system and they are involved in inflammation.

What is the meaning of HLA-B27 positive? 

Over one hundred diseases are associated with “classical” HLA class I and II genes. The most common associations are between HLA-B27 and ankylosing spondylitis or between HLA-DR4 and rheumatoid arthritis.

Let’s talk about what a positive HLA-B27 means?

The association between HLA-B27 and ankylosing spondylitis was recognized in 1973. HLA-B27 is positive for about 6 percent of  normal people in the USA. However only 2 percent of these people are developing AS over their lifetime.  But when we look at people with AS,  80 to 95 percent of these patients have an HLA- B27 positive.

Studies in healthy HLA-B27 positive individuals have a different microbial gut composition, which is distinct from the composition of the gut microbiome of HLA-B27 negative. 

Is HLA-B27 essential for a diagnosis of ankylosing spondylitis?

There are many theories about how HLA-B27 can contribute to the pathogenesis of ankylosing spondylitis. However, at this point, it is still unclear what is the role of HLA-B27 in the pathogenesis of  the disease. If you have a first or second degree relative with ankylosing spondylitis, and you test positive for HLA B27, then your risk to develop this disease is increased.

Watch this video in my Youtube channel where I go over all these questions: 

In 2013 the SpondyloArthritis International Society (ASAS) proposed an algorithm to diagnose AS. If a patient that is less than 45 years old, has chronic lower back pain persistent for more than 3 months , but has no signs of sacroiliitis on the X-Rays, then we should look for the HLA-B27.  You can find more information about how to diagnose AS, on my Youtube Channel.

If the patient has a positive  HLA-B27 and additional clinical features like:

Clinical Features for Diagnosis of Ankylosing Spondylitis
  • Inflammatory back pain
  • Heel pain
  • Sausage digits
  • Uveitis / inflammation of the eyes
  • Positive family history for SpA
  • Inflammatory bowel disease
  • Alternating buttock pain
  • Psoriasis
  • Positive response to non-steroidal anti-inflammatory drugs (NSAIDs)
  • Elevated acute phase reactants (ESR or CRP), then he/ she most likely has ankylosing spondylitis.

Remember, a positive test for HLA-B27 alone is not diagnostic for AS, while a negative test for HLA-B27 does not exclude the diagnosis of AS.

Positive HLA-B27 is not diagnostic for Ankylosing Spondylitis

HLA-B27 can be used as a screening tool in primary care in patients presenting with chronic back pain or inflammatory back pain. 

Thus, these patients with a positive HLA -B27 positive need to be sent to rheumatology for further evaluation including imaging such as X-Rays or MRI.

Navigating the medical system these days can be very challenging. If you have the proper medical support, education, and a true advocate on your side, your medical journey will become easier. Rheumatologist OnCall is a telemedicine company that offers support, diagnostic and the most advance therapeutic options for your disease in an affordable and transparent way, when you need it the most. No waiting time for months and no need to travel for tens or hundreds of miles. You can have a medical appointment from the comfort of your home.

If you have any of the symptoms of back pain or other joint pain, I strongly recommend you schedule an appointment and be evaluated by a rheumatology specialist that will provide you with an accurate diagnosis and treatment. If you are interested to learn more, check out Dr. Girnita’s online resources, including other blog posts, instagram, facebook, our Autoimmune and Arthritis support group or check out the videos on our Youtube channel.  

Contributors to this article

Diana Girnita MD, PhD and Ana Girnita

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