From the Guidelines
The HLA-B27 genetic marker test is the primary blood test used to diagnose ankylosing spondylitis. This test detects the presence of the HLA-B27 gene, which is found in approximately 90% of people with ankylosing spondylitis, as suggested by a study published in the Annals of the Rheumatic Diseases 1. However, it's essential to understand that the HLA-B27 test alone cannot confirm the diagnosis, as about 8% of the general population carries this gene without developing the condition.
Diagnosis and Screening
The study published in the Annals of the Rheumatic Diseases 1 proposes the use of HLA-B27 for screening, considering its higher sensitivity and specificity compared to inflammatory back pain. The authors suggest that HLA-B27 can be a good screening parameter, especially when the pretest likelihood has been increased to about 30-50% by the presence of other clinical or imaging parameters.
Combination with Other Tests
Doctors typically use the HLA-B27 blood test in combination with:
- Clinical symptoms
- Physical examination findings
- Imaging studies like X-rays or MRI of the sacroiliac joints and spine Other blood tests that may be ordered include inflammatory markers such as:
- Erythrocyte sedimentation rate (ESR)
- C-reactive protein (CRP) These inflammatory markers can indicate the presence of inflammation in the body but are not specific to ankylosing spondylitis, as noted in the context of chronic back pain suspected sacroiliitis-spondyloarthropathy 1.
Importance of Recent Evidence
It's crucial to rely on the most recent and highest-quality studies when making diagnostic decisions. In this case, the study published in 2005 1 provides valuable insights into the use of HLA-B27 for screening, while the 2017 study 1 focuses on the appropriateness criteria for chronic back pain suspected sacroiliitis-spondyloarthropathy, highlighting the importance of radiography and MRI in the initial evaluation.
From the Research
Blood Tests for Ankylosing Spondylitis
The diagnosis of ankylosing spondylitis (AS) often involves a combination of clinical assessment, radiological findings, and laboratory tests. Among the laboratory tests, several blood tests can be useful in aiding the diagnosis. These include:
- HLA-B27 test: This test checks for the presence of a specific genetic marker associated with an increased risk of developing AS 2, 3, 4, 5.
- Erythrocyte Sedimentation Rate (ESR): This test measures the level of inflammation in the body, which can be elevated in patients with AS 6.
- C-reactive protein (CRP): Similar to ESR, CRP is a marker of inflammation and can be used to assess disease activity in AS 6.
Interpretation of Blood Test Results
It's important to note that these blood tests are not definitive diagnostic tools on their own. For example:
- The presence of HLA-B27 does not confirm AS, as many people with this marker do not develop the disease 4.
- ESR and CRP levels can be elevated in various conditions, not just AS, and their sensitivity and specificity for assessing disease activity in AS are limited 6.
Clinical Application
The use of these blood tests should be guided by clinical judgment, taking into account the patient's symptoms, physical examination findings, and radiological results. As discussed in the studies, the HLA-B27 test can be useful in certain clinical situations to aid in diagnosis, but it should not be relied upon as the sole diagnostic criterion 2, 3, 5.