PF4 and venous thromboembolism: HIT: heparin-induced thrombocytopenia; PF4: platelet factor 4; CPB: cardiopulmonary bypass; RCT: randomized controlled trial; VTE: venous thromboembolism; THA/TKA: total hip arthroplasty/total knee arthroplasty; UFH: unfractionated heparin; LMWH: low-molecular-weight heparin; OD: optical density threshold for ELISA positivity; ELISA: enzyme-linked immunosorbent assay; SRA: serotonin release assay; HIPA: heparin-induced platelet activation test; HNA: heparin neutralization assay; PIFT: platelet immunofluorescence test; NR: not reported