title: Diagnostic Value of Procalcitonin in ANCA-Associated Vasculitis (AAV) to Differentiate Between Disease Activity, Infection and Drug Hypersensitivity.
abstract: OBJECTIVE
  Procalcitonin (PCT) is considered to be a specific marker for severe bacterial infections and sepsis. Elevated PCT levels have been reported in active autoimmune diseases without infection. The aim of this study was to assess the diagnostic value of PCT serum levels in ANCA-associated vasculitis (AAV) patients with respect to infection, disease activity and drug fever using a high sensitive PCT detection method.
  
  
  METHODS
  In 53 AAV patients with elevated C-reactive protein (CRP) PCT was determined by the Thermo Scientific BRAHMS PCT sensitive KRYPTOR assay. Patients underwent standardized diagnostic procedures for evaluation of disease activity and infection.
  
  
  RESULTS
  53 patients with AAV and elevated CRP (7.7±6.9 mg/dl, PCT 0.34±1.02 ng/ml) were assessed, 10 had infection with elevated CRP levels of 11.2±10.2 mg/dl and PCT levels of 1.06±2.07 ng/dl. 43 patients had no evidence of infection, 36 of them were presented with AAV with normal or only slightly positive PCT levels in active disease (n=36) (PCT 0.06±0.06 ng/ml). 7 patients had increased PCT levels due to azathioprine hypersensitivity (0.76±1.01 ng/ml). For discrimination between infection and vasculitis activity PCT was more useful than CRP with the best cut-off at 0.1 ng/ml (sensitivity 60%, specificity 92%).
  
  
  CONCLUSIONS
  In contrast to previous studies using semiquantitative PCT assays, the KRYPTOR performs better with respect to discrimination of infection from active AAV. In all patients assessed with active AAV (and without infection) PCT levels remained below the PCT reference limit (0.5 ng/ml) for infections. Drug hypersensitivity seems to be an important differential diagnosis in the setting of elevated CRP and PCT in patients who receive azathioprine.
authors.affiliation: Division of Rheumatology, Department of Medicine III, University Medical Center Carl Gustav Carus at the TU Dresden, Dresden, Germany ; Department of Rheumatology, Klinikum Bad Bramstedt, Germany.
authors.forename: K
authors.initials: K
authors.lastname: Herrmann
authors.affiliation: Department of Rheumatology, Klinikum Bad Bramstedt, Germany.
authors.forename: S
authors.initials: S
authors.lastname: Schinke
authors.affiliation: Department of Rheumatology, Klinikum Bad Bramstedt, Germany.
authors.forename: E
authors.initials: E
authors.lastname: Csernok
authors.affiliation: Department of Rheumatology, Klinikum Bad Bramstedt, Germany.
authors.forename: F
authors.initials: F
authors.lastname: Moosig
authors.affiliation: Department of Rheumatology, Klinikum Bad Bramstedt, Germany.
authors.forename: J U
authors.initials: JU
authors.lastname: Holle
keywords: Active vasculitis; azathioprine hypersensitivity; infection; procalcitonin