title: Negative Heparin-Induced Thrombocytopenia Test Result After Massive Transfusion:  Believe It or Not?
abstract: OBJECTIVE
  Diagnosis of heparin-induced thrombocytopenia (HIT) is complicated by a high false-positive rate for the screening enzyme immunoassay (EIA) and limited availability of confirmatory platelet activation assays such as serotonin release assay (SRA). We evaluate the impact of a massive transfusion on EIA and SRA testing and emphasize that the timing of the confirmatory sample is important.
  
  
  METHODS
  We present a case in which separate samples for HIT testing were collected before and after a major bleed requiring massive transfusion. We also discuss a recent study in which HIT serum samples were diluted in vitro and in vivo.
  
  
  RESULTS
  The EIA was strongly positive, but SRA was negative, leading to suspicion of a false-positive EIA result. However, SRA performed on the initial EIA specimen was strongly positive. A second EIA, drawn after a massive transfusion, was negative.
  
  
  CONCLUSIONS
  Replacement of several blood volumes diluted the HIT antibodies below the limit of detection. Confirmatory testing for HIT antibodies should be done on the specimen that initially tested positive.
authors.affiliation: From the Department of Pathology, Stony Brook University Medical Center, Stony Brook, NY. Lisa.senzel@sbumed.org.
authors.forename: Lisa
authors.initials: L
authors.lastname: Senzel
authors.affiliation: From the Department of Pathology, Stony Brook University Medical Center, Stony Brook, NY.
authors.forename: Daniel
authors.initials: D
authors.lastname: Coldren
mesh_terms: D000925:Anticoagulants / Q000009:adverse effects*; D001803:Blood Transfusion; D005189:False Positive Reactions; D006493:Heparin / Q000009:adverse effects*; D006801:Humans; D007124:Immunoenzyme Techniques; D008297:Male; D008875:Middle Aged; D009203:Myocardial Infarction / Q000188:drug therapy; D013921:Thrombocytopenia / Q000139:chemically induced*
chemical_list: D000925:Anticoagulants; D006493:Heparin
keywords: Dilutional effect; Heparin-induced thrombocytopenia; Transfusion