Classification Criteria Not Relevant for Diagnosis of Axial Spondyloarthritis

Classification criteria for axial spondyloarthritis are not intended for diagnosis in clinical practice and, consequently, should not be considered synonymous with diagnostic criteria, according to a paper published in Rheumatology.

“Classification criteria should only be applied to patients with an established clinical diagnosis and aimed at the identification of a more or less homogeneous group of patients for the conduction of clinical research,” wrote Denis Poddubnyy, MD, of the department of gastroenterology, infectiology, and rheumatology, at Charity-University Medicine Berlin in Germany.

The conceptual and operational differences between the twoapproaches are substantial, Dr Poddubnyy explained.

While there are no universal criteria for the diagnosis of axial spondyloarthritis, the article presented key principles of diagnosis. They include a certain level of axial spondyloarthritis probability before testing, consideration of both positive and negative results of diagnostic tests, a process of excluding other potential diagnoses, and, finally, estimation of the probability of the disease presence, expressed as a percent or in terms such as unlikely, uncertain, possible, or likely.

On the other hand, a classification approach begins with an established axial spondyloarthritis diagnosis. Consequently, little consideration is given to differential diagnoses, negative diagnostic tests are not usually considered, and a yes-or-no verdict is rendered on whether classification criteria was fulfilled, with a certain level of sensitivity and specificity.

“The sensitivity and specificity are calculated on the basis of a ‘gold standard’ that is the diagnosis established by an expert who included patients in the study on the development and/or validation of the classification criteria. Obviously, the ‘gold standard’ might be very heterogeneous and might also change over time,” Dr Poddubnyy wrote. “Thus, classification criteria should only be applied to patients with an established diagnosis.”

In short: Correct diagnosis is the main challenge in clinical practice. Correct classification pertains to research, according to the article.

—Jolynn Tumolo

Reference:
Poddubnyy D. Classification vs diagnostic criteria: the challenge of diagnosing axial spondyloarthritis. Rheumatology. 2020;59(Suppl4):iv6-iv17. https://doi.org/10.1093/rheumatology/keaa250