Immature Platelet Fraction: A Useful Marker for Identifying the Cause of Thrombocytopenia and Predicting Platelet Recovery
Authors: Lee Young Kyung , Jeon Kibum , Kim Miyoung , Lee Eunyup , Lee Jiwon , Lee Jee-Soo , Kim Hyo Jung 
Published: October 2019

Abstract
Introduction: The assessment of thrombopoietic activity in bone marrow is necessary for patients with thrombocytopenia to achieve correct diagnoses and effective treatments. We evaluated the discriminatory power of the immature platelet fraction (IPF%) in differentiating hyperdestructive/consumptive thrombocytopenia from hypoproductive thrombocytopenia, and its potential use as a predictive marker for platelet recovery.
Methods: Platelet indices including IPF% were measured in 105 healthy individuals (the control group), 31 patients with hyperdestructive/consumptive thrombocytopenia (14 with immune thrombocytopenic purpura [ITP] and 17 with liver cirrhosis), and 34 patients with hypoproductive thrombocytopenia (4 with aplastic anemia and 30 with cancer who were undergoing chemotherapy) by using a Sysmex XN-3000 hematology analyzer.
Results: The platelet number in the hyperdestructive/consumptive thrombocytopenia group was significantly lower than that in the hypoproductive thrombocytopenia group (P <0.001). The difference of plateletcrit (PCT) between the 2 thrombocytopenia groups was not statistically significant (P= 0.363). The IPF% was significantly higher in the hyperdestructive/consumptive thrombocytopenia group (median: 6.2% [IQR 4.3-10.3%]) than in both the control group (1.8% [1.3-2.4%]) and the hypoproductive thrombocytopenia group (1.8% [0.9-2.3%]) (all P-values < 0.001). However, the difference between the hypoproductive thrombocytopenia and control groups was not statistically significant (P= 0.331). Compared to the control group, the hyperdestructive/consumptive thrombocytopenia group showed a 190.5% increase in the median IPF% value, while the hypoproductive thrombocytopenia group showed a 9.5% decrease. The IPF# was significantly different between the 3groups; it was highest in the control group (median: 4.3 ×109/L [IQR 3.5-5.8×109/L]), followed by the hyperdestructive/consumptive thrombocytopenia group (3.2×109/L [1.7-4.5×109/L]), and lowest in the hypoproductive thrombocytopenia group (1.3 ×109/L [0.7-2.0×109/L]) (all P-values <0.001). Compared to the control group, the hyperdestructive/consumptive thrombocytopenia group showed a 25.6% decrease and the hypoproductive thrombocytopenia group a 69.8% decrease. PDW, MPV, and P-LCR were higher in the hyperdestructive/consumptive thrombocytopenia group (14.5 ± 3.0 fL, 12.0 fL [IQR: 11.0-12.0 fL], and 38.9 ± 6.8%, respectively) than in the other 2 groups, but there was no statistical difference between the other 2 groups. The IPF% in the hyperdestructive/consumptive group increased significantly as the number of platelets decreased, especially in patients with severe thrombocytopenia with platelet counts under 40.0 ×109/L. The IPF% was 4.7% (3.1-4.7%), 6.2% (3.2-7.6%), and 11.4% (7.1-16.6%) in patients with platelet counts>90.0 ×109/L, 40.0-90.0 ×109/L and<40.0 ×109/L, respectively (P = 0.010). However, this phenomenon was not observed in the hypoproductive thrombocytopenia group. The area under the curve (AUC) was highest for IPF% (0.938), indicating that this parameter showed the best discriminatory ability between the 2 groups, followed by PDW (0.885), P-LCR (0.859), IPF# (0.827), and MPV (0.824) (all P-values <0.001). The best IPF% cut-off value indicative of the highest sensitivity and specificity was 2.3%. The AUC of PCT was under 0.5 (0.445, P = 0.477), showing no discriminatory power. The IPF% decreased 3-4 days in advance of platelet count elevation in patients with ITP, while the IPF# ratio (compared to baseline) increased 3 days in advance of the same. Furthermore, the IPF% and IPF# ratio increased 5.5 days and 8.5 days, respectively, before platelet counts increased up to 130.0 × 109/L in cancer patients receiving chemotherapy.
Conclusion: IPF% showed the most % value difference between the 3 groups and the largest AUC, showing it has the best discriminatory power in distinguishing the cause of thrombocytopenia. Also, IPF% showed an inverse correlation with platelet count in the hyperdestructive/consumptive thrombocytopenia group, but not in the hypoproductive thrombocytopenia group. The IPF% and IPF# were useful markers to predict the elevation of platelet count in advance in ITP and in cancer patients receiving chemotherapy.

Disclosures
No relevant conflicts of interest to declare.