PF4 and Thrombocytopenia: Considering ease of collection in clinical practice, avoidance of duplicate variables, and face validity, the focus group finally selected the following parameters: (a) immunoassay test result (LIFECODES IgG PF4 enhanced), (b) platelet nadir, (c) unfractionated heparin use, (d) CRP, (e) the timing of thrombocytopenia, and (f) other causes of thrombocytopenia.