Immature platelet and reticulocyte fractions as dynamic biomarkers of bone marrow activation in dogs and humans: a comprehensive review.

BACKGROUND

: The immature platelet fraction (IPF) is a platelet-related RNA biomarker reflecting thrombopoiesis in vivo and providing immediate information about bone marrow reactivity. Despite being recognized as a reliable marker of erythropoiesis, Immature Reticulocyte Fraction (IRF) is widely utilized whereas IPF is still poorly known in spite of the diagnostic and prognostic value of this marker.

OBJECTIVES

: To review comprehensively the biology, methodology, and clinical application of IPF in humans and dogs and to assess the complementarity of IPF to IRF.

METHODS

: The current literature review was performed using PubMed/MEDLINE, Scopus, Web of Science, ScienceDirect, Google Scholar, and Cochrane Library databases. The scientific publications about the biological background, analytical validation, reference values, and clinical usage of IPF and IRF in humans and dogs that have been published until December 2025 were included and analyzed.

RESULTS

: Reference intervals of IPF depend on the analyzer used. In normal adults, IPF values are estimated as approximately 1.0-7.3% dependent on the type of Sysmex analyzer. In dogs, IPF obtained using Sysmex XN-1000 V analyzer has a reference interval of 0.5-8%, and IPF lower than 6.9% indicates central thrombocytopenia. In contrast, IRF determined using ADVIA 2120/2120i analyzer in normal large breed dogs has a reference interval of 10.4-43.5% and is significantly increased in regenerative anemia (46.5% vs. 22.1% in controls; AUC = 0.897).

CONCLUSION

: IPF is a dynamic and sensitive marker of thrombopoiesis in human and veterinary medicine. Together with IRF, it allows obtaining more complete information about bone marrow reactivity.