Differences in platelet function in patients with acute myeloid leukemia and myelodysplasia compared to equally thrombocytopenic patients with immune thrombocytopenia

Abstract

Background: Severe thrombocytopenia is a major risk factor for hemorrhage, but platelet function and bleeding risk at low platelet counts are poorly understood, because of the limitations of platelet function testing at very low platelet counts.

Objectives: To examine and compare platelet function in severely thrombocytopenic patients with acute myeloid leukemia (AML) or myelodysplasia (MDS) with that in patients with immune thrombocytopenia (ITP).

Methods: Whole blood flow cytometric measurement of platelet activation and platelet reactivity to agonists was correlated with the immature platelet fraction (IPF) and bleeding symptoms.

Results: Patients with AML/MDS had smaller platelets, lower IPF and substantially lower platelet surface expression of activated glycoprotein (GP)IIb-IIIa and GPIb, both with and without addition of ex vivo ADP or thrombin receptor-activating peptide, than patients with ITP. In both ITP and AML/MDS patients, increased platelet surface GPIb on circulating platelets and expression of activated GPIIb-IIIa and GPIb on ex vivo activated platelets correlated with a higher IPF. Whereas platelet reactivity was higher for AML/MDS patients with bleeding than for those with no bleeding, platelet reactivity was lower for ITP patients with bleeding than for those with no bleeding.

Conclusions: AML/MDS patients have lower in vivo platelet activation and ex vivo platelet reactivity than patients with ITP. The proportion of newly produced platelets correlates with the expression of platelet surface markers of activation. These differences might contribute to differences in bleeding tendency between AML/MDS and ITP patients. This study is the first to define differences in platelet function between AML/MDS patients and ITP patients with equivalent degrees of thrombocytopenia.

Figure 1

1A. Platelet count, 1B. Platelet size, 1C. Immature platelet count (IPC) and 1D. Immature platelet fraction (IPF). n = 25 for ITP, n = 21 for AML/MDS. Mean values + SEM are shown. * indicates P < 0.05; *** indicates P < 0.001. Abbreviations: AML, acute myeloid leukaemia; FLS, forward light scatter; ITP, immune thrombocytopenic purpura.

Figure 2

Expression of platelet surface activated GPIIb/IIIa (panel A), P-selectin (panel B) and GPIb (panel C) in ITP and AML/MDS patients with and without addition of platelet agonists ex vivo. n = 25 for ITP, n = 21 for AML/MDS. Mean + SEM is shown. * indicates P <0.05; ** indicates P <0.01; *** indicates P <0.001. Abbreviation: MFI, mean fluorescence intensity.

Figure 3

A. Platelet count, platelet size, immature platelet count (IPC) and immature platelet fraction (IPF) in non-splenectomized (black columns) and splenectomized patients (grey columns) with ITP. n=10 for non-splenectomized and n=15 for splenectomized patients. B. Expression of platelet surface activated GPIIb/IIIa, P-selectin and GPIb in non-splenectomized and splenectomized patients with ITP with and without addition of platelet agonists ex vivo. Mean values + SEM are shown. * indicates P < 0.05; ** indicates P < 0.01.

Figure 4

A. Correlation between markers of activation expressed on the surface of circulating platelets (i.e. with no added agonist) and immature platelet fraction (IPF%). Each dot represents an individual patient (ITP and AML/MDS combined). B. Immature platelet fraction (IPF%) vs. agonist-induced change in platelet surface GPIb expression for low and high concentrations of ADP and TRAP. The data shown are the magnitude of change in GPIb MFI following agonist stimulation as compared to the level of expression with no added agonist.

Figure 5

Expression of platelet activation markers with and without ex vivo agonist stimulation in ITP patients (left column) and AML/MDS patients (right column) with vs. without bleeding symptoms. Dark bars: no bleeding (n = 6 for ITP, n = 5 for AML/MDS). Pale bars: bleeding any site (n = 17 for ITP, n = 15 for AML/MDS). * indicates P < 0.05; ** indicates P < 0.01. Abbreviation: PSEL, P-selectin. MFI, mean fluorescence intensity.