Neutrophil PRV-1 expression across the chronic myeloproliferative disorders and in secondary or spurious polycythemia

Decreased CD177pos neutrophils in myeloid neoplasms is associated with NPM1, RUNX1, TET2, and U2AF1 S34F mutations

A decreased percentage of CD177^pos neutrophils is frequently present in MDS and AML and is a useful flow cytometry (FCM) marker for the identification of MDS. The underlying mechanism leading to the low percentage of CD177^pos neutrophils in MDS has not been explained. The aim of this study was to identify whether specific somatic mutations in myeloid neoplasms are associated with the low percentage of CD177^pos neutrophils. 507 myeloid neoplasms with one or more pathogenic molecular abnormality identified by NGS and in which CD177 expression was assessed were evaluated. Correlation with CD177 expression was determined for 39 variables (including genes mutated, diagnostic groups and gender) using a 40 % cutoff level for low CD177 expression. In multivariate analysis mutations involving NPM1 (OD 0.26), RUNX1 (OD 0.39), TET2 (OD 0.58), and U2AF1 S34F (OD 0.25) were associated with low percentage of CD177^pos neutrophils when all cases were evaluated. JAK2 (OD 2.5) alteration was associated with increased percentage of CD177^pos neutrophils. Differences were noted between diagnostic subgroups with no single mutation associated with decreased CD177^pos neutrophils in MDS and CCUS. The findings demonstrate an association between the percentage of CD177^pos neutrophils and somatically acquired mutations involving several genes.

A host-based two-gene model for the identification of bacterial infection in general clinical settings

OBJECTIVES

In this study, we aimed to develop a simple gene model to identify bacterial infection, which can be implemented in general clinical settings.

METHODS

We used a clinically availablereal-time quantitative polymerase chain reaction platform to conduct focused gene expression assays on clinical blood samples. Samples were collected from 2 tertiary hospitals.

RESULTS

We found that the 8 candidate genes for bacterial infection were significantly dysregulated in bacterial infection and displayed good performance in group classification, whereas the 2 genes for viral infection displayed poor performance. A two-gene model (S100A12 and CD177) displayed 93.0% sensitivity and 93.7% specificity in the modeling stage. In the independent validation stage, 87.8% sensitivity and 96.6% specificity were achieved in one set of case-control groups, and 93.6% sensitivity and 97.1% specificity in another set.

CONCLUSIONS

We have validated the signature genes for bacterial infection and developed a two-gene model to identify bacterial infection in general clinical settings.

CD177 expression on neutrophils: in search of a clonal assay for myeloid neoplasia by flow cytometry

OBJECTIVES

To determine whether the fraction of CD177+ neutrophils might be altered in clonal myeloid disorders, similar to the skewed κ/λ ratio for B-cell lymphomas, and could be used to identify myeloid neoplasms.

METHODS

Blood and bone marrow samples were evaluated for the fraction of CD177+ neutrophils by flow cytometry.

RESULTS

Skewed high neutrophil CD177(%) was not associated with neoplasia, but skewed low neutrophil CD177(%) was highly correlated with clonal myeloid disorders at values less than 40%. Specificity of low neutrophil CD177(%) for clonal myeloid disorders was 87% with a 40% cutoff and 95% with a 30% cutoff. Findings were most pronounced for myelodysplasia, with 52% (11/21) containing fewer than 40% CD177+ neutrophils. Specificity was also suggested by normalization of neutrophil CD177(%) in four patients who reached morphologic remission after therapy for myelodysplasia or acute leukemia.

CONCLUSIONS

Skewed low neutrophil CD177(%) is highly associated with clonal myeloid disorders, particularly myelodysplasia, and may be useful for detecting clonal myeloid disorders.

JAK2 V617F mutation and PRV-1 overexpression: relevance in the diagnosis of polycythaemia vera and essential thrombocythaemia

In the diagnosis of polycythaemia vera and essential thrombocythaemia, two molecular markers were described in the last decade: the overexpression of the PRV-1 gene and the V617F mutation in the JAK2 gene. In this study we assess their usefulness by comparing our test results with the available clinical data. We show that in the diagnosis of polycythaemia vera the JAK2 mutation screening is crucial, while testing for the PRV-1 overexpression is redundant. On the contrary, in the diagnosis of essential thrombocythaemia (ET), both JAK2 and PRV-1 show their usefulness.

Increased CD177 (PRV1) expression in thalassaemia and the underlying erythropoietic activity

CD177 (PRV1) expression is strongly related to polycythaemia vera (PV). Whilst studying CD177 expression in PV patients and controls, individuals with beta-thalassaemia minor were found to display an elevated expression of CD177. The study was expanded to include patients with thalassaemia intermedia, sickle cell/beta-thalassaemia and thalassaemia major. CD177 expression was increased in these thalassaemic groups and correlated with their erythropoietic activity, as assessed by the measurement of serum erythropoietin and soluble transferrin receptor levels. Within this context, elevated CD177 expression is not only a specific feature of PV but may be an indicator of increased erythropoietic activity in thalassaemia syndromes.

Neutrophil-specific antigen HNA-2a, NB1 glycoprotein, and CD177

PURPOSE OF REVIEW

Several advances have been made in characterization of the molecule that carries human neutrophil antigen (HNA)-2a, NB1 glycoprotein, the gene that encodes NB1 glycoprotein, CD177, and the role of antibodies to HNA-2a in transfusion reactions.

RECENT FINDINGS

NB1 glycoprotein binds to the endothelial cell adhesion molecule, platelet endothelial cell adhesion molecule-1 (PECAM-1), and participates in neutrophil transmigration. The overexpression of neutrophil CD177 mRNA has become a useful, but nonspecific biomarker of myeloproliferative diseases, especially polycythemia vera. CD177 mRNA overexpression is also a biomarker of a subset of patients with essential thrombocythemia who are at increased risk of thromboembolic complications. In patients with myeloproliferative disorders CD177 mRNA overexpression is secondary to a gain-of-function mutation in JAK2, JAK2 V617F. NB1 glycoprotein is co-localized on neutrophil plasma membranes with proteinase 3 and a complex of NB1 glycoprotein and proteinase 3 may initiate the activation of neutrophils by antineutrophil cytoplasmic antibodies in patients with Wegener's granulomatosis. The inadvertent transfusion of antibodies to HNA-2a with blood components frequently causes pulmonary transfusion reactions.

SUMMARY

The expression of CD177 is an important biomarker of myeloproliferative diseases, NB1 glycoprotein is a ligand for PECAM-1 and it may have a role in Wegener's granulomatosis, and antibodies to HNA-2a frequently cause pulmonary transfusion reactions.

Advances in molecular diagnostics of myeloproliferative disorders

Incremental advances in the molecular pathogenesis of myeloproliferative disorders (MPDs) have had a substantial impact on clinical practice in terms of both diagnosis and treatment. An array of novel molecular methods are being developed and integrated into the current battery of tests for diagnosis and monitoring of treatment response. Primarily, subjective clinico-histologic approaches to diagnosis are being replaced by more objective semimolecular diagnostic algorithms. Furthermore, identification of disease-specific molecular markers has facilitated the development of small-molecule drugs for targeted therapy. This review provides an overview of MPDs with emphasis on molecular diagnostic tests and their incorporation into contemporary diagnostic and therapeutic algorithms.

Cytogenetic and molecular aspects of Philadelphia negative chronic myeloproliferative disorders: clinical implications

Chronic myeloproliferative disorders (CMPD) are clonal disorders of the hematopoietic stem cell. The myeloid lineage shows increased proliferation with effective maturation, while peripheral leukocytosis, thrombocytosis or elevated red blood cell mass are found. In Philadelphia negative CMPD recurrent cytogenetic abnormalities occur, but no specific abnormality has been defined to date. The spectrum of cytogenetic aberrations is heterogeneous ranging from numerical gains and losses to structural changes including unbalanced translocations. The most common chromosomal abnormalities are 20q-, 13q-, 12p-, +8, +9, partial duplication of 1q, balanced translocations involving 8p11 and gains in 9p. Cytogenetic analysis of CMPD by conventional or molecular techniques has an important role in establishing the diagnosis of a malignant disease, adding also more information for disease outcome. Molecular studies may detect the possible role of candidate genes implicated in the neoplastic process, addressing new molecular target therapies. FIP1L1/PDGFRalpha rearrangements, as well as alterations of PDGFRbeta or FGFR1 gene have been found to be associated with specific types of CMPD. Recently, a novel somatic mutation, JAK2V617F, has been reported in most of the polycthemia vera (PV) patients, as well as in a lower percentage in essential thrombocythemia (ET) or idiopathic myelofibrosis (IMF) patients. This finding represents the most important advance in understanding of the molecular mechanisms underlined the pathogenesis of CMPD, contributing to the classification and management of patients.

Novel tumor antigens elicit anti-tumor humoral immune reactions in a subset of patients with polycythemia vera

We attempted to determine whether the immune reactions elicited by aberrantly expressed testis antigens contribute to the beneficial responses to interferon (IFN)-alpha therapy and other therapies in patients with polycythemia vera (PV). We screened a human testis cDNA library using SEREX (serological analysis of tumor antigens by screening an expression cDNA library with sera from three patients with PV who had undergone IFN-alpha-induced or other therapeutics-induced remission). We identified two novel PV associated tumor antigens, PV65 (eIF-2alpha) and PV13 (protamine 2). These 2 antigens elicited IgG antibody reactions in a subset of PV patients but not in healthy donors, suggesting that they are authentic tumor antigens. Increased phosphorylation of PV65 in response to stimulation of IFN-alpha, and upregulation of PV13 in tumor cells might enhance their abilities in elicitation of immune reactions in patients. These findings provide new insights into the mechanism underlying the regulation of the self-antigen repertoire in eliciting anti-tumor immune reactions in patients with polycythemia vera, and suggest their potential as the targets of novel immunotherapy.

Polycythemia Vera: New Clinicopathologic Perspectives

Context.—Polycythemia vera (PV) is a clonal myeloproliferative disease characterized by an erythroid dominant trilineage proliferation of hematopoietic precursor cells. Classified as a chronic myeloproliferative disease, PV represents a histopathologic spectrum of 2 recognized stages, the polycythemic and postpolycythemic phase. The clinical manifestations of hemorrhage, thrombosis, and increased red cell mass are directly related to primary bone marrow dysfunction. Prognosis is strongly associated with thrombosis risk and disease progression; thus, treatment is directed toward minimizing coagulopathic complications and preventing leukemic transformation. Recently, a specific point mutation in the Janus kinase 2 (JAK2) gene was described in a majority of PV patients. The potential diagnostic and/or prognostic value of JAK2V617F is discussed.

Objective.—To review important developments from the recent and historical literature. Modern diagnostic criteria and emerging molecular findings are emphasized.

Data Sources.—A comprehensive review was performed of the relevant literature indexed in PubMed (National Library of Medicine) and referenced medical texts.

Conclusions.—Modified clinical, histologic, and laboratory criteria have clarified the diagnosis of PV. Also, continuing studies on the recently discovered JAK2V617F gene mutation may significantly improve our understanding of PV pathogenesis and facilitate its medical management.

The clinical phenotype of wild-type, heterozygous, and homozygous JAK2V617F in polycythemia vera

BACKGROUND

Several studies have recently reported on the occurrence of a JAK2(V617F) mutation in myeloid cells from the majority of patients with polycythemia vera (PV). The clinical relevance of this novel observation currently is under study.

METHODS

In a single institutional study, mutation screening for JAK2(V617F) was performed in DNA derived from archived blood granulocytes from 63 consecutive patients with PV in whom current diagnostic criteria were strictly applied and the diagnosis confirmed by bone marrow histology.

RESULTS

The JAK2(V617F) mutant allele was detected in 58 of the 63 patients (92%) with 21% homozygosity. The clinical phenotype of the five patients with the wild-type allele was otherwise typical for the disease. A statistical comparison between JAK2(V617F) heterozygotes (n=45 patients) and homozygotes (n=13 patients) did not reveal any significant associations with regard to age, gender, leukocyte or platelet count at the time of diagnosis, duration of disease, or the incidences of thrombosis or bleeding. However, compared with their heterozygote counterparts, JAK2(V617F) homozygote patients displayed a significantly higher hemoglobin level at the time of diagnosis (P=0.001), an increased incidence of pruritus (69% vs. 38%; P=0.04), a higher rate of fibrotic transformation (23% vs. 2%; P=0.009), and higher PRV-1 transcript levels in their blood granulocytes (P=0.07).

CONCLUSIONS

The results of the current clinical study support previous laboratory observations that link JAK2(V617F) with the PV phenotype by demonstrating a mutant allele dose effect on erythrocytosis and clinical and laboratory features characteristic of PV.

JAK2 mutation in essential thrombocythaemia: clinical associations and long-term prognostic relevance

Clinical correlates and long-term prognostic relevance of the JAK2(V617F) mutation was studied in 150 patients with essential thrombocythaemia (ET) from a single institution and followed for a median of 11.4 years. During this period, thrombotic complications were documented in 62 patients (41.3%) and transformation into acute myeloid leukaemia (AML), polycythaemia vera (PV), or myelofibrosis with myeloid metaplasia (MMM) occurred in 4 (2.7%), 8 (5.3%), and 15 (10%) patients, respectively. JAK2(V617F) was detected in either archived bone marrow or blood cells from 73 patients (48.7%) but none were homozygous for the mutant allele. Parameters at diagnosis that were significantly associated with the presence of JAK2(V617F) included advanced age and higher counts of both haemoglobin and leucocytes. During follow-up, patients with the mutation were more likely to transform into PV but the incidences of AML, MMM, or thrombotic events were similar between patients with and without the mutation. Multivariate analysis identified advanced age, higher haemoglobin level, and thrombosis history but not the presence of JAK2(V617F) as independent predictors of inferior survival. Therefore, although the presence of JAK2(V617F) in ET appears to promote a PV phenotype, it might not carry treatment-relevant information.

Idiopathic Myelofibrosis

Idiopathic myelofibrosis (IMF) is characterized by anemia, progressive splenomegaly, bone marrow fibrosis, and extramedullary hematopoiesis. However, patients with a transitional myeloproliferative disorder (MPD), a prefibrotic form of myelofibrosis, or myelofibrosis with a fatty bone marrow share many features of IMF but have clinical characteristics that deviate from the classical description of IMF. A phenomenon that serves as a unique biomarker of IMF is the constitutive mobilization of hematopoietic progenitor cells (HPCs) and/or endothelial progenitor cells (EPCs) from the bone marrow to the peripheral blood and other extramedullary sites. Using such parameters as hemoglobin level, white blood cell count, and number of blasts in the peripheral blood, prognostic scores can be developed by which to base therapeutic decisions. Androgens, recombinant human erythropoietin (rHuEpo), and thalidomide are effective modalities of treatment of the anemia of IMF. Systemic symptoms of excess myeloproliferation are the primary indication for treatment with chemotherapeutic agents. Hydroxyurea is the most commonly used drug. Ablation of the abnormal hematopoietic clone with high-dose chemotherapy and allogeneic stem cell transplantation offers an opportunity to cure patients with IMF. The use of fully myeloablative conditioning regimens, with or without total body irradiation, is associated with a high transplant-related mortality rate (27% to 48%), especially in patients with advanced disease and in the elderly. The use of reduced intensity conditioning (RIC) regimens has resulted in prolonged survival and lower transplant-related mortality.

Concomitant neutrophil JAK2V617F mutation screening and PRV-1 expression analysis in myeloproliferative disorders and secondary polycythaemia

Polycythaemia vera (PV) is closely associated with both an acquired activating mutation of the JAK2 tyrosine kinase (JAK2(V617F)) in granulocyte-derived DNA and increased granulocyte polycythaemia rubra vera-1 (PRV-1) expression. In order to explore the correlation between these two biological markers and compare their diagnostic utility, mutation analysis for JAK2(V617F) and quantitative measurement of granulocyte PRV-1 expression were performed on the same study sample from 100 participants: 38 with PV, 22 with essential thrombocythaemia (ET), 10 with agnogenic myeloid metaplasia (AMM), 19 with secondary polycythaemia (SP) and 11 healthy volunteers. The respective overall (homozygous) JAK2(V617F) mutational frequencies were 95% (26%), 55% (0%), 30% (0%), 0% and 0%. The corresponding figures for increased PRV-1 expression were 89%, 18%, 20%, 21% and 9%. In patients with either ET or AMM, the likelihood of detecting JAK2(V617F) was significantly higher in the presence of an increased PRV-1 expression (83% vs. 38%; P = 0.05). Similarly, in patients with PV, homozygous as compared with heterozygous JAK2(V617F) correlated with higher levels of PRV-1 expression (P = 0.11). The present study suggests an allele dose-dependent effect of JAK2(V617F) on granulocyte PRV-1 expression. However, compared with the PRV-1 assay, mutation screening for JAK2(V617F) displayed greater accuracy in distinguishing PV from SP.

Chromosomal Abnormalities and Molecular Markers in Myeloproliferative Disorders

The first possibly causative molecular aberration in patients with myeloproliferative disorders has recently been described. A point mutation in the Janus kinase 2 exchanging a valine for a phenylalanine at position 617 (JAK2 V617F) was found in 65% to 97% of polycythemia vera (PV) patients, as well as in approximately 50% of essential thrombocythemia (ET) and idiopathic myelofibrosis (IMF) patients. In addition, a growing set of molecular and genetic markers, some possibly contributing to disease development, some more likely epiphenomena, has been characterized in these patients over the last few years. Compiling and synthesizing the increasing knowledge on the genetic changes observed in myeloproliferative disorder (MPD) patients will allow us to generate testable hypotheses on the molecular etiology of disease development. Therefore, this review will summarize the current knowledge on chromosomal aberrations, molecular markers, and gene expression studies in MPD patients. From these data, a model depicting our current understanding of the interplay between these markers is presented.

Bone marrow features of diagnostic impact in erythrocytosis

Controversy continues to persist about the role of histopathology regarding diagnosis of polycythemia vera (PV). For this reason, a clinicopathological study was performed on 334 patients presenting with a sustained borderline to marked erythrocytosis (hemoglobin >17 g/dl in men and >15 g/dl in women). The aim was to elucidate the discriminating impact of bone marrow biopsy examinations in an independent fashion from laboratory parameters. According to morphological findings based on a semiquantitative evaluation of standardized features, cellularity, megakaryocytes (quantity, size, pleomorphous aspect, clustering, nuclear lobulation), eosinophils, cellular debris, perivascular plasmacytosis and iron-laden macrophages exerted a distinctive value. Comparison with clinical data and follow-up revealed that in only 13 patients (4%), histopathology failed to differentiate clearly between PV (208 patients) and secondary polycythemias (113 patients). In conclusion, certain sets of morphological parameters allow a distinction between autonomous and reactive polycythemias and therefore enhance significantly diagnostic validity.

Polycythemia vera and other primary polycythemias

PURPOSE OF REVIEW

Diagnosis and therapy of polycythemia vera are controversial since the molecular basis of polycythemia vera remains unknown. Distinguishing between polycythemia vera and other polycythemic disorders can be very challenging. The purpose of this review is to discuss the recent progress in this area and critically review the published data in context of our knowledge of other polycythemic disorders.

RECENT FINDINGS

Erythropoietin is the principal regulator of regulator of erythropoiesis; its production is regulated by the degree of hypoxia. Our knowledge of cellular responses to hypoxia has recently exploded and led to the elucidation of the molecular basis of a polycythemia caused by augmentation of hypoxic sensing, Chuvash polycythemia. Similar progress in understanding the molecular basis of polycythemia vera has been elusive. A simple, readily available laboratory test to establish a diagnosis of polycythemia vera would be highly desirable; however, none exists. The value of quantization of neutrophil PRV-1 mRNA, platelet c-mpl expression, in vitro assays of erythroid progenitor cells, serum erythropoietin levels, establishing clonality in female subjects using assays employing X-chromosome-based polymorphism assays, and the progress in the chromosomal location of the gene is discussed. Integration of this information underlies the complexity of the molecular biology of polycythemia vera and indicates likely interaction of multiple genetic events in the genesis of polycythemia vera.

SUMMARY

The existence of family clustering of PV may facilitate the search for PV molecular basis. Only collaborative interaction of clinical researchers and laboratory scientists will lead to meaningful progress in determining the molecular basis of PV.

Conventional cytogenetics of myeloproliferative diseases other than CML contribute valid information

In chronic myeloproliferative disorders other than CML (CMPD) recurrent cytogenetic abnormalities occur, but specific patterns of chromosomal aberrations in the specific entities have so far not been detected. Thus, the value of conventional cytogenetics in the routine diagnostic setting of CMPD remains to be clarified. We performed a cytogenetic study on 409 patients with different CMPD [polycythemia vera, essential thrombocytosis (ET), idiopathic osteomyelofibrosis, chronic myelomonocytic leukemia (proliferative subtype), idiopathic hypereosinophilic syndrome (HES), myeloproliferative syndrome (unclassifiable)] and on 102 patients with suspected CMPD. Cytogenetic abnormalities occurred in different frequencies ranging from 3 to 40% depending on the subtype, and showed some specific differences with respect to their type. The highest frequency and the most complex pattern of clonal aberrations were observed in idiopathic osteomyelofibrosis. However, clonal aberrations were also found in 10% of patients with suspected CMPD establishing the diagnosis of a malignant disease. In conclusion, cytogenetics are essential in the routine diagnostic setting of CMPD or cases suspicious for CMPD. In ET and in HES the aberration rate was only 3 and 7%, respectively. Thus, cytogenetics can be omitted. However, in some of these cases molecular procedures should be integrated into the routine diagnostic process.

Clinical significance of neutrophil CD177 mRNA expression in Ph-negative chronic myeloproliferative disorders

The PRV-1 gene has been proposed as a marker of polycythaemia vera (PV). PRV-1 and NB1 are alleles of the polymorphic gene CD177, which belongs to the Ly-6/uPAR superfamily, and their coding regions differ at only four nucleotides. We studied neutrophil CD177 mRNA levels in normal subjects and in 235 patients with Ph-negative chronic myeloproliferative disorders (CMD), including PV, essential thrombocythaemia and myelofibrosis with myeloid metaplasia. Additional disease states were investigated for comparison. Highly variable neutrophil CD177 mRNA levels were observed in normal individuals. Neutrophils isolated from the bone marrow, or from peripheral blood following granulocyte colony-stimulating factor administration showed markedly higher CD177 expression than circulating granulocytes on steady state. Increased neutrophil CD177 mRNA levels were detected in all CMD. Elevated values were also found in reactive conditions and in disorders such as chronic myeloid leukaemia and myelodysplastic syndromes. In the differential diagnosis between PV and secondary erythrocytosis, the assay sensitivity was 68% while its specificity was 60%. These findings indicate that an elevated neutrophil CD177 mRNA level is not a specific marker for the diagnosis of PV nor for that of CMD. From a clinical viewpoint, neutrophil CD177 mRNA overexpression is rather a marker of abnormal neutrophil production and/or release in patients with CMD.

PRV-1 , erythroid colonies and platelet Mpl are unrelated to thrombosis in essential thrombocythaemia

Females with the monoclonal type of essential thrombocythaemia (ET), based on the X-chromosome inactivation pattern (XCIP), have previously been shown to present a higher incidence of thrombosis than polyclonal ones. We aimed to assess correlations between XCIP, thrombosis, and three epigenetic markers of ET, namely PRV-1 overexpression, endogenous erythroid colony (EEC) formation, and reduced platelet Mpl content. Fifty-three (60%) of 88 subjects studied had monoclonal myelopoiesis and presented a 32% incidence of major thrombosis compared with 6% of polyclonal subjects (P = 0.009). The frequency of abnormalities of PRV-1, EEC, or Mpl was similar in monoclonal and polyclonal subjects (respectively, 28%, 48%, 75%, and 37%, 27%, 63%), and none of them correlated with thrombosis. We conclude that the exploited epigenetic markers constitute independent phenotypic variations and are not clustered according to monoclonality of myelopoiesis in ET; none of them could serve as a surrogate marker of thrombotic risk in male subjects with ET.

Platelet-rich plasma serotonin levels in chronic myeloproliferative disorders: evaluation of diagnostic use and comparison with the neutrophil PRV-1 assay

In a prospective study of 109 subjects, an enzyme-linked immunosorbent assay (ELISA) was used to measure platelet-rich plasma (PRP) serotonin levels in patients with polycythaemia vera (PV; n = 27), essential thrombocythaemia (ET; n = 14), myelofibrosis with myeloid metaplasia (MMM; n = 30), secondary or spurious polycythaemia (SP; n = 22) and controls (n = 16). Nine study subjects who were taking a selective serotonin reuptake inhibitor (SSRI) all displayed a markedly decreased PRP serotonin level (median, 24.2 ng/10(9) platelets; range, 0-49.3) and were therefore excluded from further analysis. Among the remaining 100 subjects, the median and range of PRP serotonin levels, in ng/10(9) platelets, was significantly lower in MMM (89.5; 0-278.3), PV (204.8; 0-496.0) and ET (385.3; 136.8-1025.7) compared with both SP (608.8; 369.0-1780.1) and controls (567.2; 359.9-1071.1). Neutrophil polycythaemia rubra vera-1 (PRV-1) expression was concurrently assayed by real-time polymerase chain reaction in 69 patients (23 PV, 17 SP, 12 ET, seven MMM, 10 controls). PRP serotonin measurement performed as well as the PRV-1 assay in distinguishing PV from SP (93% vs. 86% test accuracy). The current study suggests that PRP serotonin concentration might be considered as one of the several biological markers that complement each other for the diagnosis of PV.