The Human Leukocyte Antigen B27 (HLA-B27) test is a laboratory procedure designed to detect a specific protein marker found on the surface of white blood cells. This protein is produced based on instructions from the inherited HLA-B27 gene. Understanding the timeline for this test involves recognizing the steps from the initial blood draw, through multi-day laboratory analysis, to the final interpretation by a healthcare provider.
Why the HLA-B27 Test is Performed
The HLA-B27 test serves as a diagnostic tool to help confirm or rule out a category of immune-mediated conditions known as spondyloarthropathies. These conditions primarily cause inflammation in the spine and other joints, and the presence of this gene is one of the strongest genetic associations with them. The test is typically ordered when a patient presents with persistent symptoms such as chronic back pain, stiffness, or signs of inflammation in the joints or eyes.
The strongest clinical link is with Ankylosing Spondylitis (AS), a progressive inflammatory disease. Up to 90% of AS patients carry the HLA-B27 gene, compared to about 8% of the general population. The test also provides context for related conditions like Reactive Arthritis, which can cause inflammation of the joints, urethra, and eyes following an infection.
Additionally, the gene is highly associated with Acute Anterior Uveitis (AAU), an inflammatory eye condition, as approximately 50% of people with AAU are HLA-B27 positive. The test is an aid, not a definitive diagnosis on its own. A positive result provides evidence considered alongside the patient’s physical symptoms, medical history, and other laboratory or imaging results.
The Sample Collection Process
The time a patient spends physically undergoing the HLA-B27 test is minimal, as it requires a standard blood draw, known as venipuncture. A healthcare professional collects a small blood sample, typically from a vein in the arm, which is then placed into a tube for transport to the laboratory. The entire collection procedure usually takes only a few minutes.
The procedure requires no special preparation from the patient; fasting or altering the diet is unnecessary. The primary requirement for the laboratory is that the whole blood specimen contains intact, viable white blood cells. For this reason, the sample must be handled carefully after collection and often kept at room temperature.
Turnaround Time for Results
The total turnaround time for HLA-B27 results is typically between three and seven business days, depending on the testing methodology and the laboratory’s logistics. The timeline is influenced by whether the sample is analyzed in-house at a local hospital lab or sent out to a specialized reference laboratory. If the sample must be shipped, the overall time can extend to ten to fourteen days due to transit time and the reference lab’s processing queue.
The two primary methods for detecting the gene also affect processing speed. Flow Cytometry is generally a faster technique because it uses fluorescent antibodies to quickly detect the HLA-B27 protein on the surface of white blood cells. Polymerase Chain Reaction (PCR) detects the DNA sequence of the gene itself. PCR is considered more definitive, but it often has a slower turnaround time and is more expensive.
It is crucial to distinguish between the laboratory processing time and the total time until the patient receives the results. Even after the lab issues the report, the ordering physician or their office must review the findings and then communicate them to the patient, which can add additional days to the total wait. The laboratory may report a result in four days, but the patient might not hear from their doctor until the end of the week or the beginning of the next week, depending heavily on the physician’s schedule.
Interpreting the Test Results
The results of an HLA-B27 test are reported simply as either positive or negative. A positive result indicates the HLA-B27 antigen was detected, meaning the patient carries the specific gene variant. This finding suggests an elevated genetic predisposition for conditions like ankylosing spondylitis and requires further clinical correlation, such as follow-up blood work or imaging studies.
A negative result means the HLA-B27 antigen was not found. While this significantly lowers the likelihood of an HLA-B27-associated disease, it does not completely exclude the possibility of a spondyloarthropathy. Conditions such as ankylosing spondylitis can still occur in individuals who do not possess the gene.
In either case, the next steps involve a consultation with the ordering physician, often a rheumatologist, to integrate the test result with the patient’s clinical presentation. A positive result often prompts additional diagnostic procedures, which may include imaging like X-rays or Magnetic Resonance Imaging (MRI) to look for signs of inflammation or structural damage. The final diagnosis is always determined by combining the genetic information, the patient’s symptoms, and the evidence from other objective tests.