It is the summ of your Symptoms, different body tests, bloodwork and mri.. done by a rheumatologist..
Good luck to you

I think they would go by your symptoms and the duration of them. They diagnose this early so hopefully you won’t progress to AS. All my bloodwork was normal and I am HLA-B27 negative.
X-rays were normal but MRI showed chronic inflammatiry changes in SI-joints. I also have it in the back of my head.
I was just diagnosed a few montgs ago but have had it for at least 15+ years.

Based on my experience, you should probably go see a rheumatologist. I have had a few different issues misdiagnosed by my family practice dr. I think an mri would show it.

I was diagnosed with a bone scan which was done 30 years ago and I have family history of spinal stenosis. I have AS.

Maybe by blood testing. Or like Elizabeth said, a rheumatoid arthritis doctor.
I had asked my family doctor and he said you do not have Nr-axSpA.
I assume he can tell me this through blood tests. My back has several issues.
Wishing you the best.