Overview
The HLA-B27 test is a laboratory test used to detect the presence of a specific protein called Human Leukocyte Antigen B27 (HLA-B27) on the surface of white blood cells. This protein is part of the HLA system, which plays an essential role in the immune system by helping the body distinguish between its own cells and harmful substances such as bacteria and viruses.
One of the most important aspects of HLA-B27 is its strong connection with several autoimmune disorders, especially diseases related to inflammation of the spine, joints, skin, eyes, and intestines. These conditions include ankylosing spondylitis, reactive arthritis, psoriatic arthritis, and uveitis. However, having HLA-B27 does not mean a person will definitely develop a disease—it only increases the risk.
Where HLA-B27 Is Produced in the Body
The HLA-B27 protein is produced inside the cells based on instructions from the HLA-B gene, which is located on chromosome 6. After the protein is formed, it is transported to the surface of white blood cells, especially lymphocytes.
Once on the cell surface, HLA-B27 helps the immune system identify harmful substances by presenting small protein pieces (antigens) to T-cells, which then activate an immune response.
Main Functions and Importance
1. Differentiates Self vs. Foreign Cells
The HLA-B27 protein allows the immune system to recognize whether a cell belongs to the body or is an invading organism like bacteria or viruses.
2. Helps Activate Immune Responses
It plays a key role in antigen presentation, a process in which harmful particles are displayed to T-cells. This signals the immune system to destroy infected or abnormal cells.
3. Important Marker in Autoimmune Diseases
Doctors often check for HLA-B27 when they suspect conditions such as:
- Ankylosing spondylitis
- Reactive arthritis
- Psoriatic arthritis
- Uveitis
- Juvenile idiopathic arthritis
- IBD-related arthritis (Crohn’s disease, ulcerative colitis)
Because HLA-B27 is strongly linked with these diseases, its presence helps support the diagnosis, especially when combined with symptoms and imaging tests.
Causes of Low/Negative Levels
The HLA-B27 test does not measure the amount of the protein. Instead, it only checks whether the protein is present or absent.
A negative result means:
- The person does not carry the HLA-B27 gene.
- It does not completely rule out autoimmune disease, but the risk is lower.
There are no “low levels” because it is a genetic marker, not a quantitative value.
Symptoms of Low/Negative Levels
A negative result has no symptoms, because it is simply a gene test.
People who test negative can still develop autoimmune diseases, but the probability is significantly reduced compared to those with HLA-B27.
Causes of High/Positive Levels
A positive HLA-B27 test indicates that the person carries the HLA-B27 gene variant.
A positive result is strongly associated with several autoimmune and inflammatory disorders, including:
- Ankylosing spondylitis – chronic inflammation of the spine
- Reactive arthritis (Reiter’s syndrome) – joint inflammation after an infection
- Psoriatic arthritis – joint inflammation linked with psoriasis
- IBD-related arthritis – arthritis seen in Crohn’s disease or ulcerative colitis
- Juvenile idiopathic arthritis – inflammatory arthritis in children
- Uveitis – inflammation inside the eye
However, many people with HLA-B27 never develop any disease.
Symptoms of High/Positive Levels
A positive HLA-B27 result itself does not cause physical symptoms. But people who carry HLA-B27 have a higher chance of developing inflammation-based diseases, which may cause symptoms like:
1. Musculoskeletal Symptoms
- Chronic lower back pain
- Morning stiffness
- Joint swelling
- Reduced spine flexibility
2. Eye Symptoms
- Redness
- Pain
- Sensitivity to light
- Blurred vision
(These may suggest uveitis)
3. Skin Symptoms
- Scaly patches (psoriatic plaques) in psoriasis
4. Gastrointestinal Symptoms
- Abdominal pain
- Diarrhea
- Blood in stools
(seen in IBD-related arthritis)
These symptoms require medical attention, especially when persistent.
Reference Range
The test results are reported as:
- Negative: HLA-B27 not detected
- Positive: HLA-B27 detected
There is no numerical reference range because this is a genetic presence/absence test.
Sample Type
- Blood sample (venous)
- Collected from a vein in the arm
- Testing methods include:
- Flow cytometry
- Genetic testing (DNA-based methods)
Test Preparation
- No fasting required.
- No dietary restrictions.
- Inform your doctor about:
- Ongoing inflammation
- Eye redness
- Back or joint pain
- Continue regular medications unless advised otherwise.
When to Consult a Doctor
You should see a doctor if you experience:
- Chronic back pain lasting more than 3 months
- Morning stiffness that improves with activity
- Unexplained joint pain or swelling
- Recurrent eye inflammation
- Persistent digestive issues
- Family history of ankylosing spondylitis or autoimmune arthritis
A positive HLA-B27 result does not confirm disease, but symptoms plus positive results need further evaluation by a rheumatologist.
Important Word Explanations
- Antigen: A substance that triggers an immune response.
- Autoimmune disease: A condition where the immune system attacks the body’s own cells.
- Lymphocytes: A type of white blood cell involved in immunity.
- Flow cytometry: A test that analyzes cells by passing them through a laser.
- Uveitis: Inflammation inside the eye.
- Ankylosing spondylitis: A form of arthritis that affects the spine.
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