Rapid flow cytometric quantitation of reticulated platelets in whole blood

Immature platelet fraction based diagnostic predictive scoring model for immune thrombocytopenia

BACKGROUND/AIMS

The diagnosis of immune thrombocytopenia (ITP) is based on clinical manifestations and there is no gold standard. Thus, even hematologic malignancy is sometimes misdiagnosed as ITP and adequate treatment is delayed. Therefore, novel diagnostic parameters are needed to distinguish ITP from other causes of thrombocytopenia. Immature platelet fraction (IPF) has been proposed as one of new parameters. In this study, we assessed the usefulness of IPF and developed a diagnostic predictive scoring model for ITP.

METHODS

We retrospectively studied 568 patients with thrombocytopenia. Blood samples were collected and IPF quantified using a fully-automated hematology analyzer. We also estimated other variables that could affect thrombocytopenia by logistic regression analysis.

RESULTS

The median IPF was significantly higher in the ITP group than in the non-ITP group (8.7% vs. 5.1%). The optimal cut-off value of IPF for differentiating ITP was 7.0%. We evaluated other laboratory variables via logistic regression analysis. IPF, hemoglobin, lactate dehydrogenase (LDH), and ferritin were statistically significant and comprised a diagnostic predictive scoring model. Our model gave points to each of variables: 1 to high hemoglobin (> 12 g/dL), low ferritin (≤ 177 ng/ mL), normal LDH (≤ upper limit of normal) and IPF ≥ 7 and < 10, 2 to IPF ≥ 10. The final score was obtained by summing the points. We defined that ITP could be predicted in patients with more than 3 points.

CONCLUSION

IPF could be a useful parameter to distinguish ITP from other causes of thrombocytopenia. We developed the predictive scoring model. This model could predict ITP with high probability.

Association of immature platelets with adverse cardiovascular outcomes

BACKGROUND

Immature platelets are less responsive to the effects of antiplatelet drugs and contain messenger ribonucleic acid that is translationally active. They can be measured easily using an automated hematoanalyzer and reported as part of the complete blood count.

OBJECTIVES

The purpose of this study was to determine the prognostic significance of elevated immature platelet count (IPC) in patients with coronary artery disease (CAD).

METHODS

In this prospective cohort study in patients with CAD, patients underwent IPC measurement and were then followed up for the composite endpoint of major adverse cardiovascular events (MACE), defined as a composite of all-cause mortality, myocardial infarction, unplanned revascularization, or hospitalization for angina. For the purposes of analysis, patients were stratified into tertiles of IPC.

RESULTS

Eighty-nine patients were followed up for a median of 31 months. Stratification to the high IPC tertile was associated with higher rates of MACE compared with the intermediate and low tertiles (60% vs. 24% vs. 16%, respectively; p < 0.001). Time-dependent receiver-operating characteristic analysis revealed that an IPC level ≥7,632 platelets/μl was 70.7% sensitive and 82.1% specific for MACE. After adjustment for age, admission diagnosis, index revascularization, heart failure, smoking, hematocrit, and baseline platelet count, patients with an IPC level ≥7,632 platelets/μl were more likely to experience a MACE (hazard ratio: 4.65; 95% confidence interval: 1.78 to 12.16; p < 0.002).

CONCLUSIONS

IPC is a novel biomarker for MACE risk stratification in patients with CAD. Future studies should focus on the utilization of this marker for individualized antiplatelet therapy.

Expression of regulatory platelet microRNAs in patients with sickle cell disease

Background

Increased platelet activation in sickle cell disease (SCD) contributes to a state of hypercoagulability and confers a risk of thromboembolic complications. The role for post-transcriptional regulation of the platelet transcriptome by microRNAs (miRNAs) in SCD has not been previously explored. This is the first study to determine whether platelets from SCD exhibit an altered miRNA expression profile.

Methods and Findings

We analyzed the expression of miRNAs isolated from platelets from a primary cohort (SCD = 19, controls = 10) and a validation cohort (SCD = 7, controls = 7) by hybridizing to the Agilent miRNA microarrays. A dramatic difference in miRNA expression profiles between patients and controls was noted in both cohorts separately. A total of 40 differentially expressed platelet miRNAs were identified as common in both cohorts (p-value 0.05, fold change>2) with 24 miRNAs downregulated. Interestingly, 14 of the 24 downregulated miRNAs were members of three families - miR-329, miR-376 and miR-154 - which localized to the epigenetically regulated, maternally imprinted chromosome 14q32 region. We validated the downregulated miRNAs, miR-376a and miR-409-3p, and an upregulated miR-1225-3p using qRT-PCR. Over-expression of the miR-1225-3p in the Meg01 cells was followed by mRNA expression profiling to identify mRNA targets. This resulted in significant transcriptional repression of 1605 transcripts. A combinatorial approach using Meg01 mRNA expression profiles following miR-1225-3p overexpression, a computational prediction analysis of miRNA target sequences and a previously published set of differentially expressed platelet transcripts from SCD patients, identified three novel platelet mRNA targets: PBXIP1, PLAGL2 and PHF20L1.

Conclusions

We have identified significant differences in functionally active platelet miRNAs in patients with SCD as compared to controls. These data provide an important inventory of differentially expressed miRNAs in SCD patients and an experimental framework for future studies of miRNAs as regulators of biological pathways in platelets.

Pathogenesis of thrombocytopenia in cyanotic congenital heart disease

Although a significant minority of patients with cyanotic congenital heart disease (CCHD) are thrombocytopenic, the pathogenesis and prevalence have not been established. This study was designed to address these 2 issues. We included 105 patients with CCHD (60 men and 45 women; aged 21 to 54 years). Systemic arterial oxygen saturations were 69% to 78%. Hematocrits were 62% to 74% with normal iron indexes. In 26 of 105 patients (25%), platelet counts were <100x10(9)/L. The diagnosis was Eisenmenger syndrome in all 26 patients with thrombocytopenia. Platelet production was determined by flow cytometric reticulated platelet counts. Megakaryocyte mass was determined indirectly by thrombopoietin levels. Disseminated intravascular coagulation was based on prothrombin time, activated partial thromboplastin time, and D-dimers. Platelet activation was determined by levels of platelet factor 4 and beta thromboglobulin. Reference ranges were derived from 20 normal acyanotic controls. A reduction in absolute reticulated platelet counts implied decreased platelet production (p<0.001). Normal thrombopoietin levels implied normal megakaryocyte mass. Normal prothrombin time, activated partial thromboplastin time, and D-dimers excluded disseminated intravascular coagulation. Normal platelet factor 4 and beta thromboglobulin indicated absent or minimal platelet activation. Twenty-five percent of the patients with CCHD were thrombocytopenic because platelet production was decreased despite normal megakaryocyte mass. We hypothesized that right-to-left shunts deliver whole megakaryocytes into the system arterial circulation, bypassing the lungs where megakaryocytic cytoplasm is fragmented into platelets, thus reducing platelet production. In conclusion, platelet counts in CCHD appear to represent a continuum beginning with low normal counts and ending with thrombocytopenia.

Assessment of an immature platelet fraction (IPF) in peripheral thrombocytopenia

A new automated method to reliably quantify reticulated platelets, expressed as the immature platelet fraction (IPF), has been developed utilizing the XE-2100 blood cell counter with upgraded software (Sysmex, Kobe, Japan). The IPF is identified by flow cytometry techniques and the use of a nucleic acid specific dye in the reticulocyte/optical platelet channel. The clinical utility of this parameter was established in the laboratory diagnosis of thrombocytopenia due to increased peripheral platelet destruction, particularly autoimmune thrombocytopenic purpura (AITP) and thrombotic thrombocytopenic purpura (TTP). Reproducibility and stability results over 48 h were good. An IPF reference range in healthy individuals was established as 1.1-6.1%, with a mean of 3.4%. Patients in whom platelet destruction might be abnormal, were studied and two of these patients followed serially during the course of treatment. The IPF was raised in several disease states. The most significant increases in IPF values were found in patients with AITP (mean 22.3%, range 9.2-33.1%) and acute TTP (mean 17.2%, range 11.2-30.9%). Following patients during treatment demonstrated that as the platelet count recovered the IPF% fell. These results show that a rapid, inexpensive automated method for measuring the IPF% is feasible and should become a standard parameter in evaluating the thrombocytopenic patient.

Comparison of reticulated platelet count and mean platelet volume determination in the evaluation of bone marrow recovery after aplastic chemotherapy

Reticulated platelet count provides an estimate of thrombopoiesis in the same way as reticulocyte count is a measure of erythropoiesis. We applied thiazole orange (TO) staining, followed by fluorescence-activated flow-cytometric analysis, to platelets in whole-blood samples from normal subjects and 18 aplastic patients after chemotherapy for haematologic malignancies. The percentage of TO-positive platelets in 30 control subjects was 5.7 +/- 2.4% (mean +/- 1 SD), determining the threshold of reticulated platelet positivity as up to 10.5% (mean + 2 SD). In the 18 patients studied, the mean percentage of TO-positive platelets was 4.3 +/- 1.89% during aplasia and 23.3 +/- 9.43% during bone marrow recovery, respectively (P < 0.05). All patients had a percentage of TO-positive platelets of up to 10.5%. In comparison, mean platelet volume during bone marrow recovery increased in 12 cases of the 18 patients studied. We conclude that flow cytometric analysis of reticulated platelets is a sensitive and specific test for evaluating thrombopoiesis recovery during aplastic chemotherapy, and platelet transfusion should be reconsidered in these patients.

Evaluation assays measuring platelet kinetics in bone marrow and peripheral blood. An overview

Platelets play an important role in haemostasis and thrombosis. For an understanding of the pathophysiology and treatment of thrombocytopenia, it is not sufficient to measure only the platelet count. Platelet kinetic parameters, such as platelet survival and turnover, might be useful because many thrombocytopenia related disorders result from the interaction between production, utilization or destruction, and sequestration of platelets. Therefore, measuring platelet turnover with radiolabelled platelets could be a sensitive and qualitative tool for clinicians. However, the method does not enjoy widespread use because it has some serious drawbacks, such as the problems associated with the manipulation of blood and platelets, and the use of radioactivity. Recently, other useful assays for measuring platelet fluxes have been described in the literature, including plasma thrombopoietin and glycocalicin. In this review, these new tests will be described, compared with the classical method using radiolabelled platelets, and finally evaluated for their usefulness in clinical practice.

Diagnostic value of tests for reticulated platelets, plasma glycocalicin, and thrombopoietin levels for discriminating between hyperdestructive and hypoplastic thrombocytopenia

We measured reticulated platelets (RPs) and plasma glycocalicin (GC) and thrombopoietin (TPO) levels simultaneously in 107 thrombocytopenic patients to clarify the diagnostic value of these tests for discriminating hyperdestructive from hypoplastic thrombocytopenia. The percentage of RPs and GC index (plasma GC level normalized for the individual platelet count) were markedly elevated in patients with idiopathic thrombocytopenic purpura (ITP) but normal or slightly elevated in patients with aplastic anemia (AA) or chemotherapy-induced thrombocytopenia (ChemoT). For RP percentage for diagnosing hyperdestructive thrombocytopenia the sensitivity and specificity were excellent but were lower for the GC index. Absolute RP counts and plasma GC levels were markedly decreased and plasma TPO levels markedly elevated in patients with AA or ChemoT, but absolute RP counts and plasma GC levels were moderately decreased and plasma TPO levels only slightly elevated in patients with ITP. The sensitivity and specificity of plasma TPO levels for diagnosing hypoplastic thrombocytopenia were excellent. Using the RP percentage and plasma TPO levels in combination improved specificities. Simultaneous measurement of RP percentage and plasma TPO level may help discriminate thrombocytopenia of unknown cause in routine hematologic practice.

Platelet activation markers and the primary antiphospholipid syndrome (PAPS)

Platelets play an important part in normal haemostasis, and are likely to be involved in the thromboembolism seen in the primary antiphospholipid syndrome (PAPS). Evidence exists for platelet activation in this disorder, and new flow cytometric techniques have made it possible to detect low levels of activation. We have previously studied the expression of the platelet activation markers CD62p and CD63, percentage of reticulated platelets, and levels of soluble P-selectin in a group of PAPS patients. Median platelet CD63 expression and plasma soluble P-selectin levels were significantly increased in PAPS patients compared to a group of controls; there was no difference in reticulated platelet percentages between the two groups. Additional assays of platelet activation (PAC-1 expression, Annexin V binding, platelet microparticles and complexes) are being developed and assessed with respect to disease activity, thrombosis risk and effects of antithrombotic therapy.

Platelet activation and turnover in the primary antiphospholipid syndrome

Thromboembolism is a common occurrence in patients with the antiphospholipid syndrome (APS). The mechanism responsible for this phenomenon is unclear; there are several theories. One possibility is that a pathogenic interaction exists between antiphospholipid antibodies and platelets, leading to their activation. This study examined the expression of the platelet activation markers CD62 and CD63 by flow cytometry in 20 patients with the primary antiphospholipid syndrome (PAPS). Levels of soluble P-selectin were also assayed. Reticulated platelets were measured as an indicator of increased platelet production and/or turnover. Median CD63 expression was significantly increased in patients (14.3%) compared to a group of healthy controls (10.1%, P = 0.0008). There was no significant difference in median CD62 expression or percent reticulated platelets between the two groups. The median level of soluble P-selectin was significantly higher in PAPS patients (35.5 ng/ml) compared to controls (18.8 ng/ml, P = 0.0028). Patients receiving aspirin had lower median CD63 values (13.1%) when compared to those patients who were not (18.0%, P = 0.023). However, aspirin therapy did not prevent significant platelet activation occurring in some individual patients. Our data suggest that although not excessive, there is a degree of increased platelet activation in some PAPS patients, which is not always suppressed by antiplatelet therapy with aspirin.

Flow cytometric analysis of reticulated platelets: evidence for a large proportion of non-specific labelling of dense granules by fluorescent dyes

The labelling of platelets with thiazole orange (TO) has been utilized by various laboratories to determine the percentage of reticulated platelets within whole blood or platelet-rich plasma (PRP). A proportion of TO labelling, however, is not entirely mRNA specific and remains to be fully defined. Almost half of the total TO-positive signal within normal platelets (n = 5) was shown to be abrogated upon degranulation with 80 microM thrombin receptor activating peptide (TRAP) (P = 0.006), strongly suggesting that platelet granules are non-specifically labelling with dye. We have confirmed this hypothesis by studying TO labelling of platelets within whole blood from dense granule deficient patients, e.g. Hermansky-Pudlak syndrome (HPS) (n = 5) and storage pool disease (SPD) (n = 4). The levels of TO-positive platelets were found to be significantly lower than normal (P = 0.0003 and P = 0.0002 respectively), but not significantly different from TRAP degranulated platelets. Upon degranulation of HPS and SPD platelets there was very little further reduction in the TO signal. Incubation of normals and SPD whole blood with different concentrations of either TO or coriphosphine-O confirmed that dense granules were non-specifically labelling even at high concentrations of both dyes. These findings suggest that although TO labelling is in part RNA specific, the dense granular pool of nucleotides appears to cause a substantial amount (approximately 50%) of non-specific labelling observed under these conditions of assay. This can easily be controlled for by a degranulation step with a non-enzymatic platelet agonist such as TRAP, and may have important consequences for the eventual standardization. clinical utilization and automation of reticulated platelet assays.