Immature Platelet Fraction in Viral Infections: A Systematic Review of Current Applications and Future Perspectives

Background: Reticulated platelets, reported by modern hematology analyzers as the immature platelet fraction (IPF%) or the absolute immature platelet count (IPC), index thrombopoiesis and have been proposed as biomarkers in the thrombocytopenia of viral infection. Methods: This systematic review, conducted and reported following PRISMA 2020 and registered in PROSPERO (CRD420261501412), examined how these parameters have been used across viral diseases. PubMed, Scopus, and the Cochrane Library were searched from January 2000 to May 2025 for observational studies of adults with viral infection reporting IPF, IPC, or reticulated platelets, and methodological robustness was appraised with the Newcastle–Ottawa Scale. Results: Twenty-two studies were included and synthesized narratively. Applications differed by pathogen: in dengue, serial IPF increases consistently preceded platelet recovery, although proposed thresholds varied; in COVID-19, higher immature platelet parameters were associated with severity and mortality but were inconsistent after adjustment. Evidence in chronic hepatitis, HIV, hantavirus, and Crimean–Congo hemorrhagic fever was mainly pathophysiological, and data in critically ill patients were almost confined to COVID-19. Conclusions: Clinical value appears disease- and outcome-specific: serial IPF best predicts platelet recovery in dengue, whereas prognostic use in COVID-19 remains insufficiently validated. Analytical heterogeneity and the absence of transferable thresholds currently limit clinical implementation.