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 diagnosis 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 HLA genes express their products on the surface of white blood cells. White blood cells are essential components of our immune system and are involved in fighting infections. Some HLA genes are expressed on all nucleated cells.
There are two 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 HLA-B27 and ankylosing spondylitis or 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, 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, your risk of developing this disease increases.
Watch this video on 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 that persists for more than three 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 diagnosing AS on my Youtube Channel.
If the patient has a positive HLA-B27 and additional clinical features like:
- Inflammatory back pain
- Heel pain
- Sausage digits
- Uveitis/inflammation of the eyes
- Positive family history for SpA
- Inflammatory bowel disease
- Alternating buttock pain
- Positive response to non-steroidal anti-inflammatory drugs (NSAIDs)
- Elevated acute phase reactants (ESR or CRP), 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.
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. Your medical journey will be easier if you have the proper medical support, education, and a true advocate. Rheumatologist OnCall is a telemedicine company that offers support, diagnostic and the most advanced therapeutic options for your disease affordably and transparently 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