Finding the right tests…
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Finding the right tests…
Molecular
HLA-B27 looks for a genetic marker on white blood cells linked to spondyloarthritis, a group of joint conditions that includes ankylosing spondylitis and reactive arthritis. This version of the test uses real-time PCR to check your DNA directly for the HLA-B27 gene, rather than the older method of mixing your blood cells with antibodies and reading the reaction under a microscope. Around 90 to 95% of people with ankylosing spondylitis carry this marker, but carrying it doesn't mean you have or will develop the disease - only about 2 to 5% of HLA-B27-positive people ever develop ankylosing spondylitis. Because of that gap, this test supports a diagnosis built on your symptoms and imaging, rather than standing alone as an answer.
A positive result means the HLA-B27 gene was detected in your DNA, which raises the likelihood of a spondyloarthritis diagnosis if you already have matching symptoms, but doesn't confirm one by itself, since the marker also shows up in people who never develop joint disease. A negative result means the gene wasn't found, which makes ankylosing spondylitis somewhat less likely but doesn't rule it out completely, since a small share of people with the disease test negative for this marker. Your doctor reads this result together with your symptoms, physical exam, and imaging rather than as a stand-alone diagnosis.
HLA-B27 is one of many human leukocyte antigen genes, a family that helps your immune system tell its own cells apart from foreign ones. Certain versions of this gene are strongly associated with a group of inflammatory joint conditions, though scientists still don't fully understand why carrying it raises that risk.
Older methods detected HLA-B27 by mixing a person's white blood cells with antibodies and checking for a reaction, a technique that could be affected by sample handling and was harder to standardise across labs. Real-time PCR instead reads the gene directly from your DNA, giving a more consistent, reproducible result regardless of which lab runs it.
The large majority of people with ankylosing spondylitis carry HLA-B27, but the reverse isn't true - only a small share of HLA-B27-positive people ever develop the condition. That gap is why this test works best as one piece of evidence alongside your symptoms and imaging, rather than something that confirms or rules out disease by itself.
A minority of people with genuine ankylosing spondylitis or related spondyloarthritis test negative for HLA-B27, so a negative result lowers the probability of these conditions without eliminating it. If your symptoms strongly suggest spondyloarthritis despite a negative test, your doctor will likely continue investigating through imaging and inflammation markers.
No. A positive result means you carry the marker, which raises your risk, but only a small share of HLA-B27-positive people ever develop ankylosing spondylitis. Your doctor combines this result with your symptoms and imaging before making a diagnosis.
Yes, it's possible, since a minority of people with genuine ankylosing spondylitis test negative for this marker. A negative result lowers the likelihood of the condition but doesn't rule it out completely, especially if your symptoms strongly suggest it.
Real-time PCR reads the HLA-B27 gene directly from your DNA, giving a more consistent result across different labs than the older antibody-based method, which could be affected by how the sample was handled.
This page is general information about the test, not medical advice. Your own report's reference ranges apply — please discuss your results with your doctor.
No, it's also associated with related conditions such as reactive arthritis and some cases of uveitis, an inflammation inside the eye. Your doctor orders this test based on which of these conditions your symptoms point toward.
It isn't recommended for that. Because most HLA-B27-positive people never develop joint disease, this test is meant to support a diagnosis in someone with relevant symptoms, not to predict future risk in someone without any.
Yes, it's a genetic marker you're born with, and it can run in families. Having a close relative with ankylosing spondylitis or a related condition is one of the reasons your doctor might consider testing for it.