title: Is hypocomplementemia useful for diagnosing or predicting extra-articular manifestations in patients with rheumatoid arthritis?
abstract: OBJECTIVE
  Serum CH50 and C4 levels are usually normal or elevated in rheumatoid arthritis (RA) but are classically decreased in patients with serious extra-articular manifestations (SEAMs) of the disease. The objective of this study was to evaluate whether complement assays are useful in diagnosing or predicting SEAMs of RA.
  
  
  METHODS
  First, a cross-sectional study of 405 patients admitted for RA compared patients with and without hypocomplementemia. Then, a retrospective longitudinal design was used to investigate within-patient complement level variations overtime.
  
  
  RESULTS
  In the univariate analysis, patients with low CH50 and C4 levels were more likely to have vasculitis and/or cryoglobulinemia than those with normal CH50 and C4 levels, and nodules were more common in the patients with low than with normal C4 levels. In a multivariate model based on symptoms, low C4 was associated with vasculitis and pleurisy and low CH50 with vasculitis. However, these associations were too weak to make CH50 and C4 determination useful for detecting SEAMs, and the within-subject variations in patients with SEAMs limited the predictive value of these assays.
  
  
  CONCLUSIONS
  Hypocomplementemia is of limited usefulness for detecting or predicting SEAMs.
authors.affiliation: Rheumatology department, CHU de Brest, France.
authors.forename: A
authors.initials: A
authors.lastname: Saraux
authors.forename: V
authors.initials: V
authors.lastname: Bourdon
authors.forename: V
authors.initials: V
authors.lastname: Devauchelle
authors.forename: P
authors.initials: P
authors.lastname: Le Goff
mesh_terms: D000328:Adult; D000368:Aged; D001172:Arthritis, Rheumatoid / Q000097:blood / Q000150:complications / Q000473:pathology; D003181:Complement C4 / Q000032:analysis; D015941:Complement Hemolytic Activity Assay; D003165:Complement System Proteins / Q000172:deficiency*; D003430:Cross-Sectional Studies; D005260:Female; D006801:Humans; D008137:Longitudinal Studies; D008297:Male; D008875:Middle Aged; D015233:Models, Statistical; D010998:Pleurisy / Q000097:blood / Q000209:etiology / Q000473:pathology; D012189:Retrospective Studies; D014657:Vasculitis / Q000097:blood / Q000209:etiology / Q000473:pathology
chemical_list: D003181:Complement C4; D003165:Complement System Proteins