Don't worry about HLA-B27. Approximately 8% of the U.S. Caucasian population carry this gene. Of that 8% only 2% will develop Spondylitis. If you carry the gene and have no other symptoms of AS, you most likely will never develop the disase. (Other ethnic groups have generally lower incidence of both the gene and disease although some very small groups have higher.) Interestingly, new research shows the incidence of HLA-B27 declines with age: Older people are less likely to have it. On the other hand, approximately 95% of people diagnosed with AS have this gene.
Go here www.asas-group.org/education/ASAS-handbook.pdf to read about criteria for diagnosing AS. As you can see, a positive HLA-B27 result is a very small part of all the different criteria used to diagnose AS.
In short, there is no reason to worry over different testing methods for HLA-B27.

Hello, I am not certain of the various specific techniques used to test for the B27 marker.  What I do know from my dr and from research is that a positive test does not mean you have AS.  (also being negative does not mean you don't have AS either).   Of all the people that test positive, only about 40% will have AS.  I believe that of those patients that are diagnosed with AS, 95% of them are positive.  There are several other factors that your dr. Will use in determining AS, being positive is only 1 factor, family history, positive response to certain medications, (NSAID), length of persistent pain, etc.
There is a more information at www.spondylitis.org
I hope that helps!
Dan

You either have the HLA-B27, or do not.   There are now sub-catagories of the HLA-B27 antigen, but still does not mean you have AS

I am not sure there is a great definition of AS.

I have had bad uveitis attacks to the point I needed cataract surgery replacing the lens on my right eye.  My back has been degenerating for many years, and I have reactive arthritis that puts me down with bad pain.   I have the HLA-B27 antigen, but the Rehumatologist I saw said I don't have AS.   My infectious disease DR calls my problems spondylarthropathies.

I test negative for the HLA B marker, but have a confirmed diagnosis based on spinal deformities on x-rays and positive family history of AS.  I'm 3rd generation, and there is no doubt.

I'm a cell biology major, and I've done both of these tests in the lab.

Flow cytometry is used to analyze and count cells, so that test likely tests for AS (maybe count white blood cells? I'm not sure).

PCR amplifies small regions of DNA so you can match regions of your DNA to known sequences of DNA. This test would be for the HLA-B27 gene.

Expect to learn if you have AS AND the HLA-B27 gene!