title: Prozone Effect in the Diagnosis of Lupus Anticoagulant for the Lupus Anticoagulant-Hypoprothrombinemia Syndrome.
abstract: OBJECTIVE
  The main clinical sequela of a lupus anticoagulant is increased thrombosis risk. However, bleeding due to lupus anticoagulant-hypoprothrombinemia syndrome is a rare but well-described manifestation of antiphospholipid syndrome. The association of acute acquired hypoprothrombinemia is caused by a lupus anticoagulant's specificity to prothrombin, which results in clearance of prothrombin and bleeding due to hypoprothrombinemia (usually <10% of normal). Severe life-threatening bleeding is most frequently reported in children with systemic lupus erythematosus or in healthy children after viral infection. In such cases, steroid therapy is usually effective in controlling the bleeding problems and improving prothrombin levels.
  
  
  METHODS
  We report one pediatric patient with a lupus anticoagulant who had acute hemorrhagic diathesis.
  
  
  RESULTS
  The diagnosis in this case was complicated by the presence of a prozone effect in lupus anticoagulant testing. The prozone effect (also known as hook effect) refers to situations where very high concentrations of antibody mask detection, typically in antigen-antibody reactions, which depend on visualization of agglutination. Decreasing the antibody/antigen ratio results in detectable antigen-antibody complexes.
  
  
  CONCLUSIONS
  We report for the first time a variation on this theme in a patient with a lupus anticoagulant-type antiphospholipid antibody and hypoprothrombinemia, which corrected with immunosuppression and restoration of normal prothrombin levels.
authors.affiliation: From the Department of Special Coagulation, Clinical Laboratory, Stanford Medical Center, Stanford, CA.
authors.forename: Jing
authors.initials: J
authors.lastname: Jin
authors.affiliation: Department of Pathology, School of Medicine, Stanford University, Stanford, CA. zehnder@stanford.edu.
authors.forename: James L
authors.initials: JL
authors.lastname: Zehnder
mesh_terms: D016736:Antiphospholipid Syndrome / Q000175:diagnosis*; D002675:Child, Preschool; D006801:Humans; D007020:Hypoprothrombinemias / Q000175:diagnosis*; D016682:Lupus Coagulation Inhibitor; D008297:Male
chemical_list: D016682:Lupus Coagulation Inhibitor
keywords: Hypoprothrombinemia; Lupus anticoagulant; Mixing study; Prozone effect