| Step | Clinical    and Lab. assessment | Action    plan | 
      
        | 1 | suspicion    of HIT | thrombocytopenia    (<150×109 /L, unexplained decrease of > 30%), timing of    over 5 days, no other cause of thrombocytopenia or thrombosis | 
      
        | 2 | ELISA    (IgG, A, M) | no    likelihood of HIT due to a negative qualitative assay | 
      
        | 3 | specific    IgG-ELISA | high    specificity for platelet-activating antibodies | 
      
        | 4 | 14C serotonin    release assay (platelet    aggregation test)
 | confirmation    of HIT as a gold standard test (not    preferable due to being less sensitive)
 | 
      
        | 5 | reassessment    of HIT if necessary | recheck    other causes of thrombocytopenia and thrombosis, assess with alternative    therapy |