How is heparin-induced thrombocytopenia (HIT) diagnosed?

Based on clinical presentation (thrombocytopenia and/or thrombosis in temporal association with heparin therapy without other obvious causes) plus presence of platelet-activating antiplatelet factor 4 (PF4)/heparin antibodies. Clinical prediction scores, especially the 4T score, are helpful in estimating the pretest probability of HIT and determining whether heparin should be discontinued and if further testing for antibodies should be carried out.