Figure 3. Qualification challenge for OA biomarkers.

A) An endotype is a subtype of a condition, which is defined by a distinct pathobiological mechanism. Thus, an endotype could potentially be identified by a specific molecular biomarker. Greater confidence in assigning endotypes could be achieved by multiple biomarkers specific to particular pathobiological mechanisms, such as inflammation in the lower example. B) However, the ability to qualify a molecular biomarker for a particular endotype is limited by the degree to which the context (mirror) for qualification--traditionally symptoms and/or imaging abnormalities of OA—are also representative of the pathobiological process of the particular endotype. Image in (B) reproduced with permission from Kraus VB. Do biochemical markers have a role in osteoarthritis diagnosis and treatment? Best Pract Res Clin Rheumatol 2006;20(1):69-80³⁴, Copyright © 2006 Elsevier Ltd.