Procalcitonin in Takayasu Arteritis

To the Editor: Procalcitonin (PCT) is an acute-phase protein, a precursor of the hormone calcitonin1. Microbial constituents and proinflammatory mediators such as tumor necrosis factor-α (TNF), interleukin 6 (IL-6), and interferon-γ induce ubiquitous PCT expression during bacterial, parasitic, or fungal infections1,2. PCT enhances inflammatory response during sepsis, when excessive PCT production can be toxic, increasing mortality in animal models1. In humans, PCT has been demonstrated to be a more accurate marker of systemic bacterial infections than C-reactive protein (CRP)3, and it correlates with the severity of sepsis and mortality risk1. For these reasons, PCT is increasingly used for diagnosis, prognostic stratification, and treatment of patients with systemic bacterial or fungal infections. However, PCT elevation has been reported in noninfectious conditions, including inflammatory states associated with antineutrophil cytoplasmic antibodies-associated vasculitis, Kawasaki disease, and Goodpasture syndrome2. The clinical usefulness of PCT as a biomarker in patients with systemic autoimmune diseases has not been fully defined2. One metaanalysis showed that PCT had higher specificity but lower sensitivity than … Address correspondence to Dr. E. Tombetti, San Raffaele University Hospital, Unit of Internal Medicine and Clinical Immunology, Via Olgettina 60, 20132 Milan, Italy. E-mail: tombetti.enrico{at}hsr.it