The HLA-B27 test is a blood test that detects the presence of the human leukocyte antigen B27 (HLA-B27) protein on the surface of white blood cells. This protein is part of the body's immune system and helps distinguish between its own cells and foreign substances.
Understanding HLA-B27
- Human Leukocyte Antigens (HLAs): These proteins are found on the surface of nearly every cell in the body. They play a critical role in the immune system's ability to recognize and respond to foreign invaders like bacteria and viruses.
- HLA-B27: This is a specific type of HLA. While it's normal for HLAs to vary from person to person, the presence of HLA-B27 is associated with an increased risk of developing certain autoimmune diseases.
Purpose of the HLA-B27 Test
The HLA-B27 test is primarily used to help diagnose or rule out certain autoimmune and inflammatory conditions, particularly those affecting the spine and joints.
- Ankylosing Spondylitis: A chronic inflammatory disease that primarily affects the spine.
- Reactive Arthritis: Joint pain and swelling triggered by an infection in another part of the body.
- Psoriatic Arthritis: A form of arthritis that affects people with psoriasis.
- Juvenile Idiopathic Arthritis: A type of arthritis that affects children.
- Uveitis: Inflammation of the middle layer of the eye (uvea).
It's important to note that having HLA-B27 does not guarantee that a person will develop any of these diseases, it simply indicates an increased risk. Many people with HLA-B27 never develop associated health problems. Conversely, it is also possible to have one of the diseases listed above and not have HLA-B27.
How the Test is Performed
The HLA-B27 test requires a blood sample, which is typically drawn from a vein in the arm. No special preparation is usually needed. The blood sample is then sent to a laboratory for analysis. The lab will determine if the HLA-B27 protein is present on the white blood cells.
Interpreting the Results
- Positive Result: A positive result means that the HLA-B27 protein was detected in the blood sample. This suggests an increased risk for certain autoimmune diseases, but further evaluation and clinical correlation are necessary to establish a definitive diagnosis.
- Negative Result: A negative result means that the HLA-B27 protein was not detected in the blood sample. This makes certain diagnoses less likely, but it does not completely rule them out.
| Result | Meaning |
|---|---|
| Positive | HLA-B27 protein is present; indicates increased risk for certain autoimmune diseases. |
| Negative | HLA-B27 protein is not detected; makes certain diagnoses less likely but does not rule them out entirely. |
