HLA B27 Flow Cytometry

HLA, short for human leukocyte antigen, is a protein present on our white blood cells (cells that help the body fight against infections). This protein helps the immune system identify the body’s own cells and distinguish them from harmful germs and foreign substances. There are several types of HLAs, and each person inherits a unique set of these proteins from their parents. HLA-B27 is a specific HLA type found on white blood cells in some people, and its presence is associated with certain health conditions, particularly autoimmune diseases. These are conditions in which the body’s immune system mistakenly attacks its own healthy tissues rather than protecting them.

The HLA-B27 test is a blood test that checks for the presence or absence of the human leukocyte antigen-B27 on an individual's white blood cells. It is also known as the human leukocyte antigen B27 test, ankylosing spondylitis-HLA test, psoriatic arthritis-HLA test, and reactive arthritis-HLA test.

This test helps doctors check for autoimmune diseases such as ankylosing spondylitis (which causes spine pain and stiffness), reactive arthritis (joint pain after an infection), juvenile rheumatoid arthritis (a joint disease in children that causes pain and swelling), and eye inflammation called uveitis (which causes red, painful eyes).

The test mainly focuses on the immune system and how it affects joints (spine, neck, chest), eyes, and sometimes the gut, where pain, swelling, and long-term inflammation can occur. Although it does not confirm a disease on its own, the HLA-B27 test supports diagnosis based on symptoms and findings of other tests, such as the rheumatoid factor (RF) test, erythrocyte sedimentation rate (ESR), and C-reactive protein (CRP).

The HLA-B27 test is done when a doctor thinks a person may have certain autoimmune conditions that affect the joints, spine, or eyes. You may need this test if you have symptoms like:

• Ongoing pain and swelling in the spine, neck, or chest
• Gradual stiffness in the back that makes movement difficult over time
• Long-term joint pain with inflammation that feels like arthritis
• Repeated eye problems such as redness, pain, or blurred vision (uveitis)

This test may be recommended for:

• Individuals suspected of having a spine disease like ankylosing spondylitis (causing back pain and stiffness)
• Individuals with joint pain that started after an infection (reactive arthritis)
• Patients with repeated eye inflammation (uveitis), causing redness and pain, or skin rashes
• Young adults (below 40 years) with long-term joint or back pain
• Individuals with a family history of autoimmune diseases
• Patients with relevant findings for inflammatory arthritis with other blood tests (like RF, ESR, CRP)

The HLA B27 test procedure does not require routine repeated testing and is usually performed based on specific clinical needs.

The HLA-B27 test report is used to support the evaluation of certain autoimmune and joint-related conditions. The following conditions may be assessed with the help of this test:

• Ankylosing spondylitis: A long-term arthritis that mainly affects the lower spine and pelvis joints, causing pain, swelling, and stiffness. Over time, the bones in the spine may slowly fuse together.
• Psoriatic arthritis: A form of arthritis seen in people with a skin problem called psoriasis.
• Reactive arthritis (Reiter’s syndrome): A type of arthritis that develops after an infection and may also affect the eyes, skin, and urinary or genital systems.
• Juvenile rheumatoid arthritis: A type of arthritis seen in children and teenagers, which can cause joint pain, swelling, and stiffness.
• Uveitis: Inflammation of the middle layer of the eye, which can cause redness, pain, and blurred vision.
• Inflammatory bowel disease (Crohn’s disease or ulcerative colitis): Joint pain that happens along with bowel (stomach/intestine) disease.
• Sacroiliitis: Inflammation of the joint where the lower spine connects to the hip bones.

What to Expect Before the HLA B27 Test

No fasting is required for a standalone HLA B27 test. You can eat and drink normally. However, if it is part of a broader package that includes fasting tests, your doctor may advise fasting for 8-12 hours. Avoid strenuous exercise for 24 hours before the test, as intense physical activity can temporarily raise HLA B27 levels and affect interpretation. Always inform your doctor about any ongoing medications.

What to Expect During the Blood Collection

A phlebotomist cleans the skin with an antiseptic, then places an elastic band around your upper arm to make the veins easier to access. A small needle is inserted into the vein; you may feel a brief pinch. Blood is collected into a labelled tube in under a minute.

What to Expect After the HLA B27 Test

A small cotton swab and bandage are placed over the site to stop any minor bleeding. You can return to normal activities immediately. Minor bruising is normal and disappears quickly. If dizzy, sit and rest for a few minutes.

This test measures a single key parameter related to immune and genetic markers:

• HLA-B27 (Human Leukocyte Antigen B27): A protein on white blood cells that helps identify the body’s own cells and is associated with certain immune-related joint and spine diseases.

The HLA-B27 test is a qualitative test, meaning it does not have a numerical “normal range.” Instead, the results are reported as either positive or negative.

Note

• This test is usually done using the HLA B27 flow cytometry test (a laboratory method that checks for specific proteins on blood cells using special machines).

The table below shows what different HLA-B27 test results may mean.

Important Note:

• A positive result does not always mean disease, as some healthy people may also have HLA-B27.
• This test cannot tell the exact disease, severity, or future outcome.

The HLA B27 blood test is generally safe, but minor risks, which are rare and resolve quickly, include:

• Mild pain at the blood draw site
• Slight bruising or bleeding
• Feeling dizzy or lightheaded.

Understanding HLA B27 Test Limitations

• Results should always be interpreted along with symptoms and clinical findings.
• The test may rarely show a false positive result because the testing antibodies can sometimes react with similar HLA proteins in the blood.
• This test alone cannot confirm a disease, because bone and joint changes may take years to appear, and the test only supports diagnosis. So, additional tests may be needed for confirmation.
• HLA-B27 is inherited from parents and has different subtypes (like B2705 and B2702), but its exact role in disease risk is still not fully known.

If HLA-B27 blood test results need further evaluation, additional tests may be done to better understand joint pain, inflammation, and related conditions. These may include:

• Anti-CCP antibody test
• C-reactive protein (CRP) test
• Erythrocyte sedimentation rate (ESR) test
• Rheumatoid factor (RF) test
• X-rays (used to look for changes or damage in bones and joints)

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