title: Evaluation of pretest clinical score (4 T's) for the diagnosis of heparin-induced thrombocytopenia in two clinical settings.
abstract: BACKGROUND
  Heparin-induced thrombocytopenia (HIT) is a prothrombotic adverse drug reaction caused by heparin. As thrombocytopenia is common in hospitalized patients receiving heparin, it would be useful to have a clinical scoring system that could differentiate patients with HIT from those with other reasons for thrombocytopenia.
  
  
  OBJECTIVE
  To compare prospectively the diagnostic utility of a clinical score for HIT in two different clinical settings.
  
  
  METHODS
  The pretest clinical scoring system, the '4 T's', was used to classify 100 consecutive patients referred for possible HIT in one hospital (Hamilton General Hospital, HGH) into high, intermediate, and low probability groups. This system was also used to classify likewise 236 patients by clinicians in Germany referring blood for diagnostic testing for HIT in Greifswald (GW). The clinical scores were correlated with the results of laboratory testing for HIT antibodies using the serologic criteria for HIT with high diagnostic specificity.
  
  
  RESULTS
  In both centers, patients with low scores were unlikely to test positive for HIT antibodies [HGH: 1/64 (1.6%), GW: 0/55 (0%)]. Patients with intermediate [HGH: 8/28 (28.6%), GW: 11/139 (7.9%)] or high scores [HGH: 8/8 (100%), GW: 9/42 (21.4%)] were more likely to test positive for clinically significant HIT antibodies. The positive predictive value of an intermediate or high clinical score for clinically significant HIT antibodies was higher at one center (HGH).
  
  
  CONCLUSIONS
  A low pretest clinical score for HIT seems to be suitable for ruling out HIT in most situations (high-negative predictive value). The implications of an intermediate or high score vary in different clinical settings.
authors.affiliation: Department of Medicine, McMaster University, Hamilton, ON, Canada.
authors.forename: G K
authors.initials: GK
authors.lastname: Lo
authors.forename: D
authors.initials: D
authors.lastname: Juhl
authors.forename: T E
authors.initials: TE
authors.lastname: Warkentin
authors.forename: C S
authors.initials: CS
authors.lastname: Sigouin
authors.forename: P
authors.initials: P
authors.lastname: Eichler
authors.forename: A
authors.initials: A
authors.lastname: Greinacher
mesh_terms: D000328:Adult; D000368:Aged; D000465:Algorithms; D004797:Enzyme-Linked Immunosorbent Assay; D005260:Female; D006493:Heparin / Q000009:adverse effects*; D006801:Humans; D007124:Immunoenzyme Techniques; D007388:Internal Medicine / Q000379:methods; D008297:Male; D008875:Middle Aged; D011237:Predictive Value of Tests; D011446:Prospective Studies; D012680:Sensitivity and Specificity; D013921:Thrombocytopenia / Q000139:chemically induced* / Q000175:diagnosis* / Q000276:immunology
chemical_list: D006493:Heparin