title: Clinical and laboratory characteristics associated with a high optical density anti-platelet factor 4 ELISA test.
abstract: OBJECTIVE
  Diagnosing heparin-induced thrombocytopenia, a potentially catastrophic immune-mediated disorder, continues to pose significant challenges for clinicians, as both clinical and laboratory tools lack specificity. There is mounting evidence supporting a positive correlation between definitive heparin-induced thrombocytopenia and optical density (OD) positivity from the widely available anti-platelet factor 4 enzyme-linked immunosorbent assays (PF4 ELISAs). However, the clinical features distinguishing these patients remain poorly understood.
  
  
  METHODS
  To better characterize this group, we conducted a case-controlled, retrospective chart review of patients from two large, urban academic institutions who underwent a PF4 ELISA at a central laboratory. Associations between OD and 18 clinical characteristics were calculated using the Fisher's exact test for categorical variables and Wilcoxon rank-sum test for continuous variables.
  
  
  RESULTS
  In total, 184 negative patients (OD <0.7), and 121 positive patients (OD >0.7), including 74 low-positive patients (0.7< OD <1.4) and 47 high-positive patients (OD >1.4) were identified. Several clinical variables were significantly different in the negative group compared with the positive group, including hospital day (P<0.001), previous admission within the past 3 months (P<0.001), and the presence of a new thrombus (P=0.003). However, many of these variables were not different between the negative and low-positive group, and were only distinct between the negative and high-positive group. When the low-positive and high-positive groups were compared, only the 4T score was significantly different (P=0.003).
  
  
  CONCLUSIONS
  These data indicate that those with OD >1.4 form a distinct clinical group and support the clinical utility of the 4T score.
authors.affiliation: Department of Medicine, NYU School of Medicine, New York, NY, USA.
authors.forename: Benjamin Y
authors.initials: BY
authors.lastname: Lu
authors.affiliation: Department of Medicine, NYU School of Medicine, New York, NY, USA.
authors.forename: David
authors.initials: D
authors.lastname: Kudlowitz
authors.affiliation: Department of Medicine, NYU School of Medicine, New York, NY, USA ; Department of Biochemistry and Molecular Pharmacology, NYU School of Medicine, New York, NY, USA ; The Perlmutter Cancer Center, NYU Langone Medical Center, NYU School of Medicine, New York, NY, USA.
authors.forename: Lawrence B
authors.initials: LB
authors.lastname: Gardner
keywords: HIT; heparin; heparin-induced thrombocytopenia; platelet factor 4 ELISA; thrombocytopenia