HLA-B27: Meaning, Test & Associated Diseases
HLA-B27 is a genetic marker found on white blood cells that is associated with certain joint and spinal conditions. A positive result increases the risk of diseases such as ankylosing spondylitis.
Things worth knowing about "HLA-B27"
HLA-B27 is a genetic marker found on white blood cells that is associated with certain joint and spinal conditions. A positive result increases the risk of diseases such as ankylosing spondylitis.
What is HLA-B27?
HLA-B27 (Human Leukocyte Antigen B27) is a specific protein molecule found on the surface of immune system cells. It belongs to the group of MHC class I molecules (Major Histocompatibility Complex) and plays a central role in regulating immune responses. The marker is encoded by genes on chromosome 6 and is inherited.
In Central European populations, approximately 6–9% of people carry the HLA-B27 marker. A positive result is not proof of disease but rather a genetic risk factor.
Biological Function
HLA molecules present short protein fragments (peptides) to the immune system – both self-derived and foreign ones (e.g., from bacteria or viruses). This allows the immune system to recognize whether a cell is healthy or needs to be attacked. Under certain conditions, HLA-B27 can form misfolded protein structures or overactivate immune cells, which may promote inflammatory responses.
Associated Conditions
HLA-B27 is strongly associated with a group of conditions known as spondyloarthritides. These include:
- Ankylosing Spondylitis (Morbus Bechterew): A chronic inflammatory disease of the spine and sacroiliac joints. Approximately 90% of those affected are HLA-B27 positive.
- Reactive Arthritis (formerly Reiter syndrome): Joint inflammation following an infection (e.g., with Chlamydia or Salmonella).
- Psoriatic Arthritis: Joint inflammation associated with psoriasis.
- Enteropathic Arthritis: Joint inflammation related to inflammatory bowel diseases such as Crohn's disease or ulcerative colitis.
- Acute Anterior Uveitis: Inflammation of the front part of the eye.
Importantly, not every person with HLA-B27 develops one of these conditions. Only approximately 1–5% of HLA-B27-positive individuals develop spondyloarthritis.
Diagnosis – The HLA-B27 Test
The HLA-B27 test is a straightforward blood test that examines the presence of the antigen on white blood cells (leukocytes). Analysis is typically performed using flow cytometry or molecular genetic methods (PCR).
When is the Test Ordered?
- When an inflammatory spinal condition is suspected (e.g., chronic low back pain in young adults)
- To support the diagnosis of spondyloarthritis
- In cases of unexplained uveitis or reactive arthritis
- As part of the workup for joint inflammation of unclear origin
Interpretation of Results
A positive result means that the HLA-B27 antigen has been detected. This increases the risk of certain conditions but does not confirm active disease. A negative result does not completely rule out spondyloarthritis, as a small percentage of affected individuals are HLA-B27 negative.
Clinical Relevance
The HLA-B27 test is an important diagnostic tool that is evaluated in combination with clinical findings, imaging (MRI, X-ray), and laboratory values (e.g., CRP, ESR). It does not replace a complete rheumatological workup but provides valuable clues in the early detection of spondyloarthritides.
References
- Sieper J. et al. – Ankylosing spondylitis: an overview. Annals of the Rheumatic Diseases, 2002.
- German Society for Rheumatology (DGRh) – S3 Guideline Axial Spondyloarthritis, 2019.
- Khan MA – HLA-B27 and its subtypes in world populations. Current Opinion in Rheumatology, 1995.
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