HLA-B27 (Ankylosing Spondylitis & Spondyloarthritis)
Also known as: Human Leukocyte Antigen B27, HLA-B27 PCR, Ankylosing Spondylitis Gene Test, HLA-B27 Flow Cytometry
Parameters Measured in the Report
A breakdown of individual biomarkers and biological reference intervals typically found in your report:
| Biomarker | Standard Range | Unit | What It Means |
|---|---|---|---|
HLA-B27 (PCR / Flow Cytometry) (HLA-B27 Allele) | Negative / Absent | qualitative | Molecular genetic or cytometric detection of the HLA-B27 surface antigen; positive in >90% of ankylosing spondylitis patients. |
* Note: Reference ranges may vary slightly between testing instruments and reagent kits. Always refer to the reference interval printed on your specific pathology report.
Clinical Focus
Genetic presence of the Human Leukocyte Antigen B27 allele encoded in the Major Histocompatibility Complex (MHC Class I) on chromosome 6.
Sample & Specimen
Venous blood (EDTA lavender-top tube)
Fasting Protocol
No fasting required. Maintain regular water intake.
Turnaround Time
24–48 hours
What Is This Test?
Why Did Your Doctor Order This Test?
Physicians routinely prescribe the HLA-B27 in the following clinical scenarios:
How to Prepare Before Your Test
- No fasting or special preparation required.
- Because HLA-B27 is an inherited genetic marker, the result never changes over your lifetime — it only ever needs to be tested once.
Understanding Your Results
What higher or lower readings generally mean in clinical practice:
If Values Are Higher Than Normal
A Positive HLA-B27 result in a patient experiencing chronic inflammatory back pain or radiographic sacroiliitis strongly supports the diagnosis of Ankylosing Spondylitis or Axial Spondyloarthritis, guiding prompt treatment with NSAIDs and anti-TNF / anti-IL-17 biologic therapies.
If Values Are Lower Than Normal
A Negative result means the HLA-B27 allele is absent. While >90% of AS patients are positive, approximately 5% to 8% of genuine ankylosing spondylitis patients are HLA-B27 negative, meaning a negative test does not entirely rule out spondyloarthritis if imaging shows definitive sacroiliitis.
Frequently Asked Questions
Does testing positive for HLA-B27 mean I will definitely develop Ankylosing Spondylitis?
No. Approximately 6% to 8% of healthy individuals carry the HLA-B27 gene, but only about 2% to 5% of HLA-B27 positive people ever develop ankylosing spondylitis. It represents genetic susceptibility, not an inevitable diagnosis.
Do I ever need to repeat an HLA-B27 test?
No. Because HLA-B27 is your inherited genetic DNA, your result is permanent. A single high-quality PCR or flow cytometry test is valid for life.
Related Laboratory Tests
Tests frequently prescribed together or used as follow-up investigations:
Inflammatory Markers (ESR & C-Reactive Protein / hs-CRP)
Rate of red blood cell settling (ESR) and hepatic acute-phase reactant protein concentration (CRP / hs-CRP).
Rheumatoid Factor (RF) & Anti-CCP (Rheumatoid Arthritis Panel)
IgM autoantibodies against IgG Fc portion (Rheumatoid Factor) and highly specific autoantibodies against cyclic citrullinated peptides (Anti-CCP).
ANA (Antinuclear Antibodies by IFA — HEp-2)
Autoantibodies directed against cellular nuclear antigens, reported with end-point titer dilution and morphological staining pattern.
Medical & Diagnostic Disclaimer
This guide is published for educational and patient informational purposes only. It is not a substitute for professional medical evaluation, diagnosis, or clinical advice.
A laboratory result that falls slightly outside standard statistical reference intervals does not automatically indicate disease; conversely, a normal result does not guarantee the absence of medical conditions. Only your attending physician can interpret lab findings in the context of your medical history, physical exam, and symptoms.