There is no ONE test or procedure that can accurately diagnose or rule out Ankylosing Spondylitis.  Therefore, diagnosis is made based on a combination of factors.  Each of these factors are like pieces of a puzzle that your Doctor (typically a Rheumatologist) must put together for an accurate diagnosis:

1.    A history of inflammatory back pain that has persisted for more than 3 months chronically

2.    Pain in your SI joints that are asymmetrical and alternate

3.    Positive for the HLA-B27 gene test

4.    A family history of Ankylosing Spondylitis, IBD, or PsA

5.    An elevation in CRP and/or SED Rate (blood tests that indication inflammation)

6.    X rays, particularly of the SI joints

7.    If x rays do not reveal anything significant, than an MRI

8.    Negative RF Factor (blood test that rules out Rheumatoid Arthritis)

9.    Physical examination testing for range of motion and tenderness

10.  History of fatigue

11.  History of Plantar Fasciitis

12.  Onset of symptoms typically occurred before the age of 45

13.  The pain is worse at night and early in the morning, and improves with movement & physical activity

14.  A possible history of Iritis or Uveitis (eye inflammation)

15.  A history of IBS or Inflammatory Bowel Disease, such as Crohns

During an exam, your doctor may ask you to bend in certain directions to determine if there are any restrictions in the range of movement.  They also may press on locations near joints and in between vertebrae to search for sites of tenderness resulting from inflammation.  


They will also take blood work and send it off to a lab.   They may want to search for the RF Factor, to rule out the possibility of Rheumatoid Arthritis.  The RF Factor is not associated with Ankylosing Spondylitis.  At the same time, they will no doubt search to see if your levels of C Reactive Protein and SED Rate (also called ESR) are elevated.  This indicates inflammation.  However, not all patients with AS have elevated levels of these markers.  Or they may have elevations that come and go, based upon whether the disease is in a state of activity or remission at the moment.  Also, these markers for inflammation can be elevated due to other conditions.

Another blood test likely to be ordered is to check if you are HLA-B27 positive.  This gene is found in only 8% of the Caucasian population of the world.  However, not everyone with the gene will actually develop Ankylosing Spondylitis.  An environmental trigger is involved in those who actually develop the disease.  Among Caucasians who have AS, the gene is found in 95% of the cases.  Among those from a Mediterranean descent, it is found in 80% of the cases  (However, among African Americans, the gene is only found in 50% of the cases).  This gene, therefore, has a very strong connection to the disease, but it is not the only gene that has been discovered to have a link to this type of arthritis. Currently, there are over 100 genetic influences reported to have an influence in the manifestation of this disease. * Some of the other well known genes involved besides HLA-B27 are ERAP1, IL1A and IL23R.  Therefore, if a person is negative for HLA-B27, the Doctor might choose to test for these other genes.

X-rays will probably be ordered of your lower back, paying particular attention to the SI joints, looking for signs of erosion or sacroilitis.  However, it is well known that it may take 7-10 years of disease activity before changes in the SI joints are significant enough to appear on a conventional x-ray.  Therefore, the lack of radiological evidence is not a sufficient reason for a Physician to rule out a diagnosis of Ankylosing Spondylitis, especially if there are other positive indications for such a diagnosis.  An MRI can reveal changes in the joints earlier than an x ray and may be ordered if an x ray does not reveal anything, however the cost of an MRI is sometimes problematic.

It is not always easy to diagnose AS because the symptoms often present gradually.  In the beginning, a person might just believe they have common back strain, or a back injury of some sort.  So they do not get evaluated by a doctor.  Even if they do go to get evaluated by a doctor,  evidence of the disease is typically not visible on imaging until the patient has suffered with symptoms for many years.  Plus, Ankylosing Spondylitis does not present itself exactly in the same way for every person.  This is especially true among women.  For example, some women have reported that the symptoms of AS started in their neck rather than in their lower back.  They have a higher incidence of peripheral pain, as well as bowel involvement. For all of these reasons, it is not uncommon for a delay in diagnosis. 


Even worse, many patients are initially misdiagnosed.  According to research done by, 96% of people who ultimately get diagnosed with AS had at least one misdiagnosis first.  This is especially a problem with women, since symptoms can present slightly different and some doctors still are under the false premise that Ankylosing Spondylitis is a man's disease.   Earlier studies indicated that the ratio of men to women who have AS is 9 to 1.  But more recent studies show that now, the ratio is 2 to 1, or maybe 3 to 1.  Still, some doctors are under the impression, either consciously or unconsciously,  that AS is a man's disease.   Another factor is that when women have widespread pain, they are sometimes misdiagnosed as having fibromyalgia, since there are some overlapping symptoms with AS.  A misdiagnosis, whether you are a man or woman, not only leads to a delay in getting the treatment that you need, but it also may put you on unnecessary treatments or medications with unnecessary risks and side effects that will not help your AS at all.

Even if you are not misdiagnosed,  a delay in diagnosis is still a problem for both genders, although the delay is significantly longer for women, for the reasons explained above.  A large study from 2017 that totaled 23,889 patients (32% of them were women) showed that the average delay in diagnosis for males was 6.5 years, whereas the delay for women was a staggering 8.8 years. 

However, ruling out other conditions that could explain the ongoing chronic pain, checking for some of the known genetic markers, as well as possible inflammation in blood tests, exploring family history of the disease, and looking for a type of pain that is uniquely worse after resting at night, can give Ankylosing Spondylitis a "foot print" that helps to identify it,  with or without evidence that appears on imaging.  It is important to get a diagnosis as soon as possible so that treatments can begin without delay to help modify the course of the disease, slow it down, and prevent possible fusing of the spine.

* ERAP1 Association With Ankylosing Spondylitis is Attributable to Common Genotypes Rather Than Rare Haplotype Combinations, Proc. Natl. Acad. Sci. USA 2017, Vol. 114 (3), Amity R Roberts, 558-561, doi: 10.1073/pnas.1618856114

Arthritis & Rheumatism (Arthritis Care & Research), Vol. 59, No. 3, March 15, 2008, pp 449–454, DOI 10.1002/art.23321

J Rheumatol. 2017 Feb;44(2):174-183. doi: 10.3899/jrheum.160825. Epub 2016 Dec 15