Immature Platelet Fraction in Different Diagnosis of Thrombocytopenic States: An Approach to Distinguish Idiopathic Thrombocytopenic Purpura from Myelodysplastic Syndrome with Isolated Thrombocytopenia.

It is sometimes confusing to distinguish idiopathic thrombocytopenic purpura (ITP) from thrombocytopenia due to dysmegakaryopoiesis, as seen in myelodysplastic syndrome (MDS) patients, especially MDS with isolated thrombocytopenia. In this study, we investigated the useful parameters for the different diagnosis of thrombocytopenia. The number of reticulated platelets reflects the rate of thrombopoiesis, and this clinical utility has been established in the laboratory diagnosis of thrombocytopenia due to increased peripheral platelet destruction, such as autoimmune thrombocytopenic purpura (AITP). However, the number of reticulated platelets has not been well investigated in the patients with myelodysplatsic syndrome (MDS), while some of them are misdiagnosed as ITP. The aim of this study is to evaluate the diagnostic utility of the measurements of reticulated platelets as well as other parameters of platelets, such as MPV (mean platelet volume), P-LCR (platelet larger cell ratio) and PDW (platelet distribution width). The reticulated platelets, expressed as the immature platelet fraction (IPF) were determined in 108 ITP and 57 MDS patients using the Sysmex XE-2100 blood cell counter with upgraded software (Sysmex, Kobe, Japan). This system enabled rapid, inexpensive, automated, stable measurements of reticulated platelets compared with the flow cytometry system, of which consensus method has not yet been identified to provide acceptable intra- and inter-laboratory results.

The platelet counts in ITP and MDS patients were equivalent (ITP, 7.99 ± 0.40 × 10⁴/μL; MDS, 8.05 ± 0.57× 10⁴/μL). The IPF values in ITP patients (10.4 ± 0.61%) were significantly higher than those in MDS (5.82 ± 0.63%), and the inverse correlation between the IPF and the platelet counts was observed among the ITP patients, but not among the MDS. Both MPV and PDW in MDS (10.6 +/− 0.15 fL and 12.2+/−0.41 fL, respectively) were significantly higher than in ITP (7.7 +/− 0.38 fL and 9.4 +/− 0.48 fL, respectively), while P-LCR in MDS (28.7 +/− 1.2%) and ITP (23.6 +/− 1.3%) were not significantly different. Although MPV was correlated with IPF among either group, the correlation between IPF and either PDW or P-LCR was weak among MDS (IPF × PDW, r=0.673; IPF × P-LCR, r=0.660) compared with ITP (IPF × PDW, r=0.779; IPF × P-LCR, r=0.803). Next we precisely investigated the clinical features of the minor population of MDS with higher IPF. Most of these patients revealed the significantly higher values of PAIgG (Platelet-associated IgG) and/or poor response to the blood transfusion, suggesting the possibility of associated autoimmune mechanisms. The patients of MDS in overt leukemic stage also recorded higher IPF even if they had no or few blood transfusion. The IPF would be a useful parameter to distinguish ITP from MDS with isolated thrombocytopenia, which has been shown to have a favorable prognosis.