Late and/or chronic periprosthetic joint infection in patients with total joint replacements can be very difficult to diagnose, and evaluation of the levels of serum inflammatory markers is one of the more commonly done diagnostic tests when periprosthetic joint infection is considered. Unfortunately, inflammatory arthritis, in its many forms, is a common etiology of joint destruction leading to arthroplasty, results in mild or moderate degrees of immunocompromise, and is associated with persistent, baseline elevations in levels of inflammatory biomarkers. Because of this terrible triad, patients with inflammatory arthritis may be at greater risk of chronic periprosthetic joint infection, and such infections may be harder to diagnose because elevations in inflammatory markers may reflect the underlying disease rather than infection of the prosthetic joint. Until now, very little actual information has existed to aid clinicians who face the difficult task of trying to diagnose an infection at the site of a joint replacement in a patient with known inflammatory arthritis. In fact, a workgroup consisting of members of the Musculoskeletal Infection Society recently proposed a new definition of periprosthetic joint infection, but none of the studies on which they based their work included patients with underlying inflammatory diseases1. Thus, a number of important …