PPBP and bacterial infectious disease: Different platelet indices, such as PNLR (platelet-to-neutrophil/lymphocyte ratio), PNR (platelet-to-neutrophil ratio) and secreted proteins, such as sP-selectin, CXCL4, CXCL7, and serotonin, have been studied as markers to discriminate viral and bacterial infection pathogenesis [15].