Elevation of serum thrombopoietin precedes thrombocytosis in acute infections

Pathophysiology, classification, and complications of common asymptomatic thrombocytosis in newborn infants

We frequently encounter newborn infants with thrombocytosis in the neonatal intensive care unit. However, neonatal thrombocytosis is not yet fully understood. Thrombocytosis is more frequently identified in newborns and young infants, notably more often in those younger than 2 years than in older children or adults. The production of megakaryocytes (megakaryopoiesis) and platelets (thrombopoiesis) is mainly regulated by thrombopoietin (TPO). Increased TPO levels during infection or inflammation can stimulate megakaryopoiesis, resulting in thrombopoiesis. TPO concentrations are higher in newborn infants than in adults. Levels increase after birth, peak on the second day after birth, and start decreasing at 1 month of age. Initial platelet counts at birth increase with gestational age. Thus, preterm infants have lower initial platelet counts at birth than late-preterm or term infants. Postnatal thrombocytosis is more frequently observed in preterm infants than in term infants. A high TPO concentration and low TPO receptor expression on platelets leading to elevated plasma-free TPO, increased sensitivity of megakaryocyte precursor cells to TPO, a decreased red blood cell count, and immaturity of platelet regulation are speculated to induce thrombocytosis in preterm infants. Thrombocytosis in newborn infants is considered a reactive process (secondary thrombocytosis) following infection, acute/chronic inflammation, or anemia. Thrombocytosis in newborn infants is benign, resolves spontaneously, and, unlike in adults, is rarely associated with hemorrhagic and thromboembolic complications.

Therapeutic Plateletpheresis in Patients With Thrombocytosis: Gender, Hemoglobin Before Apheresis Significantly Affect Collection Efficiency

Background: Thrombocytosis is a common symptom in myeloproliferative neoplasms (MPN), and excessive proliferation may deteriorate into thrombosis, bleeding, myelofibrosis, and may ultimately convert to acute leukemia. This study aimed to investigate the collection efficiency of plateletpheresis (CEPP) and factors influencing its efficacy in patients with thrombocytosis.

Materials and Methods: From September 2010 to December 2016, 81 patients from two institutions in China with myeloproliferative neoplasms and thrombocytosis accompanied by severe symptoms were treated with plateletpheresis by Fresenius COM. TEC machine.

Results: After apheresis, the median CEPP was 20.71% (IQR: 9.99–36.69%) and median PLT reduction rate was 25.87% (IQR: 21.78–36.23%). Further analysis showed that no significant difference was observed between PLT count with 800–1,000 × 10⁹/L and > 1,000 × 10⁹/L. The PLT counts significantly decreased (P < 0.001) after plateletpheresis, the red blood cell (RBC), white blood cell (WBC), hemoglobin (HGB), and hematocrit (HCT) levels showed no significant differences before- or after- plateletpheresis. Multivariate analysis showed that female sex (P = 0.009) and HGB (P = 0.010) before apheresis were associated with CEPP. Female (P = 0.022), HCT (P = 0.001) and blood volume (P = 0.015) were associated with the PLT reduction rate. Furthermore, symptoms were relieved after apheresis in patients whose PLT count was 800–1,000 × 10⁹/L accompanied with symptoms.

Conclusions: It is reasonable to perform plateletpheresis when the PLT count is over 800 × 10⁹/L and patients are complicated by clinical symptoms such as dizziness, headache, somnolence, and stupor. Plateletpheresis is effective in removing PLTs especially in females with high HGB.

Essential Thrombocythemia in Children and Adolescents

Simple Summary

Among chronic Ph-negative myeloproliferative neoplasms, essential thrombocythemia is found in children with low but increasing incidence. The diagnostic and clinical features do not completely overlap with ET of adult age. A significant number of cases, in fact, do not meet the criteria of clonality, and many cases require extensive clinical evaluation to exclude secondary, reactive forms. Therefore, histological analysis of bone marrow biopsy is necessary, and its use should be enforced. The clinical course appears to be more benign, at least within the first decades of observation, with the incidence of thrombotic events being much lower than in adults (4 % vs. 30%). Hemorrhages are mostly irrelevant. Therefore, the management should be carefully adapted to the individual patient, balancing the risk of future complications with long-term collateral effects of any drug. This review analyzes the peculiarities of the disease facing similarities and differences with adult scenarios.

Abstract

This paper reviews the features of pediatric essential thrombocythemia (ET). ET is a rare disease in children, challenging pediatric and adult hematologists alike. The current WHO classification acknowledges classical Philadelphia-negative MPNs and defines diagnostic criteria, mainly encompassing adult cases. The presence of one of three driver mutations (JAK2V617F, CALR, and MPL mutations) represent the proof of clonality typical of ET. Pediatric ET cases are thus usually confronted by adult approaches. These can fit only some patients, because only 25–40% of cases present one of the driver mutations. The diagnosis of hereditary, familial thrombocytosis and the exclusion of reactive/secondary thrombocytosis must be part of the diagnostic process in children and can clarify most of the negative cases. Still, many children present a clinical, histological picture of ET, with a molecular triple wild-type status. Moreover, prognosis seems more benign, at least within the first few decades of follow-up. Thrombotic events are rare, and only minor hemorrhages are ordinarily observed. As per the management, the need to control symptoms must be balanced with the collateral effects of lifelong drug therapy. We conclude that these differences concert a compelling case for a very careful therapeutic approach and advocate for the importance of further cooperative studies.

The implications of platelet count changes during hospitalization in the disease management of paediatric patients with bronchiolitis

BACKGROUND

The objective of this study was to investigate the significance of the platelet count on admission and platelet count changes during hospitalization in paediatric patients with bronchiolitis.

METHODS

Clinical data from 404 consecutive patients hospitalized for bronchiolitis were collected and compared after grouping according to the platelet count on admission and the delta platelet count during hospitalization (the platelet count 3-5 days after admission minus the platelet count on admission; Group A, delta platelet count < -50 × 10⁹/L; Group B, -50 × 10⁹/L ≤ delta platelet count ≤ 50 × 10⁹/L; Group C, delta platelet count > 50 × 10⁹/L).

RESULTS

Thrombocytosis was found in 79 (19.6%) patients, while 325 (80.4%) patients had a normal platelet count on admission. There was no difference in disease severity between these two groups. Groups A, B and C comprised 57 (14.1%), 133 (32.9%) and 214 (53.0%) patients, respectively. The patients from Group A had longer periods of oxygen therapy and stay in the paediatric intensive care unit, and a greater frequency of mechanical ventilation than the patients from Group B or Group C (all p < .05). Notably, among all the patients, the delta platelet count negatively correlated with the numbers of days of oxygen therapy (r = -0.385, p < .001) and stay in the paediatric intensive care unit (r = -0.603, p < .001).

CONCLUSIONS

A decrease in the platelet count during hospitalization in paediatric patients with bronchiolitis may provide useful information for disease management.

Immunothrombotic Dysregulation in COVID-19 Pneumonia Is Associated With Respiratory Failure and Coagulopathy

Supplemental Digital Content is available in the text.

Background:

Severe acute respiratory syndrome corona virus 2 infection causes severe pneumonia (coronavirus disease 2019 [COVID-19]), but the mechanisms of subsequent respiratory failure and complicating renal and myocardial involvement are poorly understood. In addition, a systemic prothrombotic phenotype has been reported in patients with COVID-19.

Methods:

A total of 62 subjects were included in our study (n=38 patients with reverse transcriptase polymerase chain reaction–confirmed COVID-19 and n=24 non–COVID-19 controls). We performed histopathologic assessment of autopsy cases, surface marker–based phenotyping of neutrophils and platelets, and functional assays for platelet, neutrophil functions, and coagulation tests, as well.

Results:

We provide evidence that organ involvement and prothrombotic features in COVID-19 are linked by immunothrombosis. We show that, in COVID-19, inflammatory microvascular thrombi are present in the lung, kidney, and heart, containing neutrophil extracellular traps associated with platelets and fibrin. Patients with COVID-19 also present with neutrophil-platelet aggregates and a distinct neutrophil and platelet activation pattern in blood, which changes with disease severity. Whereas cases of intermediate severity show an exhausted platelet and hyporeactive neutrophil phenotype, patients severely affected with COVID-19 are characterized by excessive platelet and neutrophil activation in comparison with healthy controls and non–COVID-19 pneumonia. Dysregulated immunothrombosis in severe acute respiratory syndrome corona virus 2 pneumonia is linked to both acute respiratory distress syndrome and systemic hypercoagulability.

Conclusions:

Taken together, our data point to immunothrombotic dysregulation as a key marker of disease severity in COVID-19. Further work is necessary to determine the role of immunothrombosis in COVID-19.

Activation of toll-like receptors 2 and 4 on CD34+ cells increases human megakaryo/thrombopoiesis induced by thrombopoietin

BACKGROUND

Platelet Toll-like receptor (TLR)2/4 are key players in amplifying the host immune response; however, their role in human megakaryo/thrombopoiesis has not yet been defined.

OBJECTIVES

We evaluated whether Pam3CSK4 or lipopolysaccharide (LPS), TLR2/4 ligands respectively, modulate human megakaryocyte development and platelet production.

METHODS

CD34+ cells from human umbilical cord were stimulated with LPS or Pam3CSK4 with or without thrombopoietin (TPO).

RESULTS

CD34+ cells and megakaryocytes express TLR2 and TLR4 at both RNA and protein level; however, direct stimulation of CD34+ cells with LPS or Pam3CSK4 had no effect on cell growth. Interestingly, both TLR ligands markedly increased TPO-induced CD34+ cell proliferation, megakaryocyte number and maturity, proplatelet and platelet production when added at day 0. In contrast, this synergism was not observed when TLR agonists were added 7 days after TPO addition. Interleukin-6 (IL-6) release was observed upon CD34+ or megakaryocyte stimulation with LPS or Pam3CSK4 but not with TPO and this effect was potentiated in combination with TPO. The increased proliferation and IL-6 production induced by TPO + LPS or Pam3CSK4 were suppressed by TLR2/4 or IL-6 neutralizing antibodies, as well as by PI3K/AKT and nuclear factor-κB inhibitors. Additionally, increased proplatelet and platelet production were associated with enhanced nuclear translocation of nuclear factor-E2. Finally, the supernatants of CD34+ cells stimulated with TPO+LPS-induced CFU-M colonies.

CONCLUSIONS

Our data suggest that the activation of TLR2 and TLR4 in CD34+ cells and megakaryocytes in the presence of TPO may contribute to warrant platelet provision during infection episodes by an autocrine IL-6 loop triggered by PI3K/NF-κB axes.

A cross-sectional retrospective study to analyze the underlying causes and clinical characteristics of children with reactive thrombocytosis at a Korean tertiary medical center

Background

Reactive thrombocytosis (RT) is a common condition among children, although no studies have examined the etiology or clinical characteristics of RT among Korean children.

Methods

This retrospective study evaluated children with RT at a single Korean tertiary center during a 10-year period.

Results

RT accounted for 13.5% of children who were admitted to the pediatric ward (4,113/30,355): mild RT, 82.7%; moderate RT, 14.1%; severe RT, 1.1%; and extreme RT, 2.1%. There was a negative correlation between platelet count and Hb level (P=0.008). There were positive correlations between platelet count and WBC (P=0.001), erythrocyte sedimentation rate (ESR) (P=0.007), and admission duration (P=0.006). The most common cause of RT was infection and the second most common was Kawasaki disease (KD). The highest proportion of lower respiratory tract infection was observed in extreme RT (P<0.001). The proportion of KD was highest in extreme RT (P<0.001) and in children aged 1–7.9 years (P<0.001). The proportion of refractory KD was highest in extreme RT (P=0.005). In cases of KD, there was a positive correlation between platelet count and fever duration (P=0.006). Non-KD autoimmune inflammation was only observed in mild/moderate RT, and its proportion was highest in children aged 8–18 years (P<0.001).

Conclusion

In children, more severe RT was associated with lower Hb, increased WBC, ESR, and prolonged admission. With respiratory infection or KD, extreme RT was associated with more severe disease course.

It's reticulated: the liver at the heart of atherosclerosis

Platelets play a critical role in both the initiation and progression of atherosclerosis, and even more so in the ensuing atherothrombotic complications. Low-dose aspirin remains the mainstay of antiplatelet therapy in high-risk patients by reducing the risk of myocardial ischemia, stroke or death due to cardiovascular disease. However, antiplatelet therapies lose their efficacy in people with diabetes mellitus, increasing the risk of future atherothrombotic events. The molecular mechanisms that promote platelet hyperactivity remain unclear but could be due to glycation-induced conformational changes of platelet membranes resulting in impaired aspirin entry or less-efficient acetylation/compensatory increase in COX-2 expression in newborn platelets. Emerging evidence from our laboratory and elsewhere suggest that enhanced platelet turnover (thrombopoiesis), particularly the production of immature reticulated platelets from the bone marrow, could contribute to atherosclerotic complications. We have identified a major role for neutrophil-derived S100A8/A9, a damage-associated molecular pattern, in driving reticulated thrombopoiesis by directly interacting with its receptors on Kupffer cells in the liver. In this review, we discuss the role of hepatic inflammation in driving reticulated platelet production and suggest potential targets to control their production, improve efficacy of current antiplatelet therapies and reduce the risk of atherothrombotic complications.

Time course of immature platelet count and its relation to thrombocytopenia and mortality in patients with sepsis

Introduction

The pathogenesis of thrombocytopenia in patients with sepsis is not fully understood. The aims of this study were to investigate changes in thrombopoietic activity over time by using absolute immature platelet counts (AIPC) and to examine the impact of platelet production on thrombocytopenia and mortality in patients with sepsis.

Methods

This retrospective observational study included adult patients with sepsis admitted to the intensive care unit at a university hospital. Two hundred five consecutive sepsis patients were stratified into four groups according to nadir platelet count: severe (nadir ≤40×10³/μL), moderate (41–80×10³/μL), or mild thrombocytopenia (81–120×10³/μL), or normal-increased platelet count (>120×10³/μL). The development of thrombocytopenia was assessed during the first week; mortality was assessed at day 28.

Result

Of the 205 patients included, 61 (29.8%) developed severe thrombocytopenia. On admission, AIPC did not differ among the four groups. In patients with severe thrombocytopenia, AIPC decreased significantly from days 2 to 7, but remained within or above the normal range in the other three groups (overall group comparison, P<0.0001). Multivariate analysis including coagulation biomarkers revealed that AIPC was independently associated with the development of severe thrombocytopenia (day 3 AIPC, odds ratio 0.49 [95% confidence interval (CI) 0.35–0.66], P<0.0001; day 5 AIPC, 0.59 [95% CI 0.45–0.75], P<0.0001). AIPC was a significant predictor of 28-day mortality in Cox hazard models adjusted for Acute Physiology and Chronic Health Evaluation II and Sequential Organ Failure Assessment scores (day 3 AIPC, hazard ratio 0.70 [95% CI 0.52–0.89], P = 0.0029; day 5 AIPC, 0.68 [95% CI 0.49–0.87], P = 0.0012).

Conclusions

Thrombopoietic activity was generally maintained in the acute phase of sepsis. However, a decrease in AIPC after admission was independently associated with the development of severe thrombocytopenia and mortality, suggesting the importance of suppressed thrombopoiesis in the pathophysiology of sepsis-induced thrombocytopenia.

Significance of platelet count in children admitted with bronchiolitis

AIM

To determine the true prevalence of thrombocytosis in children less than 2 years of age with bronchiolitis, its association with risk factors, disease severity and thromboembolic complications.

METHODS

A retrospective observational medical chart review of 305 infants aged two years or less hospitalized for bronchiolitis. Clinical outcomes included disease severity, duration of hospital stay, admission to pediatric intensive care unit, or death. They also included complications of thrombocytosis, including thromboembolic complications such as cerebrovascular accident, acute coronary syndrome, deep venous thrombosis, pulmonary embolus, mesenteric thrombosis and arterial thrombosis and also hemorrhagic complications such as bleeding (spontaneous hemorrhage in the skin, mucous membranes, gastrointestinal, respiratory, or genitourinary tracts).

RESULTS

The median age was 4.7 mo and 179 were males (59%). Respiratory syncytial virus was isolated in 268 (84%), adenovirus in 23 (7%) and influenza virus A or B in 13 (4%). Thrombocytosis (platelet count > 500 × 10⁹/L) occurred in 88 (29%; 95%CI: 24%-34%), more commonly in younger infants with the platelet count declining with age. There was no significant association with the duration of illness, temperature on admission, white blood cell count, serum C-reactive protein concentration, length of hospital stay or admission to the intensive care unit. No death, thrombotic or hemorrhagic events occurred.

CONCLUSION

Thrombocytosis is common in children under two years of age admitted with bronchiolitis. It is not associated with disease severity or thromboembolic complications.

Global hemostasis in healthy bitches during pregnancy and at different estrous cycle stages: Evaluation of routine hemostatic tests and thromboelastometry

This study assessed the global hemostasis (including prothrombin time [PT], activated partial thromboplastin time [aPTT], antithrombin activity [ATA], fibrinogen and d-Dimer concentrations, platelet count, plateletcrit and thromboelastometry) in healthy pregnant bitches, comparing the results with those of healthy bitches at different estrous cycle stages, and assessed whether hemostatic changes during pregnancy are associated with serum progesterone concentration or the presence of fetuses in utero. The results show that pregnant bitches have higher fibrinogen concentration, platelet count and platelatecrit, and that fibrin and global clot formations occur faster than in non-pregnant bitches at different estrous cycle stages. Additionally, clot strength was higher in pregnant bitches than in non-pregnant ones. There were no differences in PT, ATA, and D-dimer concentration between all study groups. The aPTT was significantly shorter in bitches at the fourth and last pregnancy weeks, compared to the anestrus group, and shorter in both the fourth and last pregnancy weeks groups, compared to diestrus group. These results all support a hypercoagulable state in healthy pregnant bitches, unassociated with progesterone concentration.

Association between secondary thrombocytosis and viral respiratory tract infections in children

Secondary thrombocytosis (ST) is frequently observed in children with a variety of clinical conditions. The leading cause of ST is respiratory tract infection (RTI) in children. Nasopharyngeal aspirate samples were collected and assessed for common respiratory viruses. The relationships between virus infections and secondary thrombocytosis were analyzed retrospectively. The blood platelet count and the presence of respiratory viruses were determined for 3156 RTI patients, and 817 (25.9%) cases with platelet ≥500 × 10(9)/L were considered as the thrombocytosis group. Compared with the normal group, the detection rates of respiratory syncytial virus (RSV) and human rhinovirus (HRV) were significantly higher in the thrombocytosis group (P = 0.017 and 0.042, respectively). HRV single infection was a risk factor associated with thrombocytosis [odds ratio (OR) = 1.560, 95% confidence interval (CI) = 1.108-2.197]. Furthermore, ST was more likely to occur in younger patients who had clinical manifestations of wheezing and dyspnea and who had been diagnosed with bronchiolitis. Furthermore, the course of disease lasted longer in these patients. ST is associated with viral respiratory tract infections, especially RSV and HRV infections. HRV single infection is a risk factor associated with thrombocytosis.

Primary thrombocytosis in children

Myeloproliferative neoplasms are uncommon disorders in children, for which we have limited understanding of the pathogenesis and optimal management. JAK2 and MPL mutations, while common drivers of myeloproliferative neoplasms in adult patients, are not clearly linked to pediatric disease. Management and clinical outcomes in adults have been well delineated with defined recommendations for risk stratification and treatment. This is not the case for pediatric patients, for whom there is neither a standard approach to workup nor any consensus regarding management. This review will discuss thrombocytosis in children, including causes of thrombocytosis in children, the limited knowledge we have regarding pediatric primary thrombocytosis, and our thoughts on potential risk stratification and management, and future questions to be answered by laboratory research and collaborative clinical study.

Increased Thrombopoiesis and Platelet Activation in Hantavirus-Infected Patients

BACKGROUND

Thrombocytopenia is a common finding during viral hemorrhagic fever, which includes hemorrhagic fever with renal syndrome (HFRS). The 2 main causes for thrombocytopenia are impaired thrombopoiesis and/or increased peripheral destruction of platelets. In addition, there is an increased intravascular coagulation risk during HFRS, which could be due to platelet activation.

METHODS

Thrombopoiesis was determined by quantification of platelet counts, thrombopoietin, immature platelet fraction, and mean platelet volume during HFRS. The in vivo platelet activation was determined by quantification of soluble P-selectin (sP-selectin) and glycoprotein VI (sGPVI). The function of circulating platelets was determined by ex vivo stimulation followed by flow cytometry analysis of platelet surface-bound fibrinogen and P-selectin exposure. Intravascular coagulation during disease was determined by scoring for disseminated intravascular coagulation (DIC) and recording thromboembolic complications.

RESULTS

The levels of thrombopoietin, immature platelet fraction, and mean platelet volume all indicate increased thrombopoiesis during HFRS. Circulating platelets had reduced ex vivo function during disease compared to follow-up. Most interestingly, we observed significantly increased in vivo platelet activation in HFRS patients with intravascular coagulation (DIC and thromboembolic complications) as shown by sP-selectin and sGPVI levels.

CONCLUSIONS

HFRS patients have increased thrombopoiesis and platelet activation, which contributes to intravascular coagulation.

Intermittent X-linked thrombocytopenia with a novel WAS gene mutation

X-linked thrombocytopenia (XLT) is caused by mutations in the WAS gene and characterized by thrombocytopenia with minimal or no immunodeficiency. Patients with XLT usually exhibit persistent thrombocytopenia, and intermittent thrombocytopenia has been described only in two families. Here, we report a patient with intermittent XLT carrying a novel missense mutation (Ala56Thr). He showed residual expression of Wiskott-Aldrich syndrome protein in the lymphocytes and platelets. There appeared to be an association between normal platelet numbers and a post infectious state. Our findings further support the importance of analysis of Wiskott-Aldrich syndrome protein in male patients who exhibit fluctuating courses of thrombocytopenia.

New insights into thrombopoiesis in neonatal sepsis

Thrombocytopenia is one of the most frequent hematologic abnormalities in the neonatal period, affecting about 18-35% of all patients admitted to the Neonatal Intensive Care Unit (NICU), with sepsis being among the most common causes of severe neonatal thrombocytopenia. It is unclear whether decreased platelet production or increased platelet consumption contributes to thrombocytopenia of septic neonates. To answer this question, we evaluated the effects of sepsis on neonatal thrombopoiesis using a panel of tests. This prospective case-control study was conducted on 50 neonates with culture-proven sepsis admitted to NICU at the Pediatrics Department, Ain Shams University Hospitals. Thirty healthy newborns were included as controls. The enrolled neonates were subjected to detailed history taking, thorough clinical examination, and laboratory investigations including complete blood count, C-reactive protein, blood cultures, and tests of thrombopoiesis; namely serum thrombopoietin (TPO) assay, flow cytometric analysis of reticulated platelet percentage (RP%), and calculation of absolute RP counts. Septic neonates comprised 24 males and 26 females with a mean gestational age of 36.0 ± 3.1 weeks. Twenty-eight (56%) of the septic neonates were thrombocytopenic (platelets < 150 000/µl). While platelet and RP counts were decreased, TPO and RP% were increased in septic neonates compared to healthy controls. Neonates with Gram-negative sepsis had the lowest platelet and RP counts and the highest TPO and RP% followed by those with fungal septicemia. Platelet counts showed inverse correlations with TPO and RP% and direct correlation with RP count. Our findings suggest that neonates respond to sepsis by up-regulating thrombopoiesis, where thrombocytopenia ensues when the rate of platelet consumption exceeds the rate of platelet production. Simultaneous measurements of serum TPO levels and RP% are helpful in discriminating hyperdestructive from hypoplastic thrombocytopenia among septic neonates.

Thrombopoietin as biomarker and mediator of cardiovascular damage in critical diseases

Thrombopoietin (TPO) is a humoral growth factor originally identified for its ability to stimulate the proliferation and differentiation of megakaryocytes. In addition to its actions on thrombopoiesis, TPO directly modulates the homeostatic potential of mature platelets by influencing their response to several stimuli. In particular, TPO does not induce platelet aggregation per se but is able to enhance platelet aggregation in response to different agonists (“priming effect”). Our research group was actively involved, in the last years, in characterizing the effects of TPO in several human critical diseases. In particular, we found that TPO enhances platelet activation and monocyte-platelet interaction in patients with unstable angina, chronic cigarette smokers, and patients with burn injury and burn injury complicated with sepsis. Moreover, we showed that TPO negatively modulates myocardial contractility by stimulating its receptor c-Mpl on cardiomyocytes and the subsequent production of NO, and it mediates the cardiodepressant activity exerted in vitro by serum of septic shock patients by cooperating with TNF-α and IL-1β. This paper will summarize the most recent results obtained by our research group on the pathogenic role of elevated TPO levels in these diseases and discuss them together with other recently published important studies on this topic.

Thrombocytosis: diagnostic evaluation, thrombotic risk stratification, and risk-based management strategies

Thrombocytosis is a commonly encountered clinical scenario, with a large proportion of cases discovered incidentally. The differential diagnosis for thrombocytosis is broad and the diagnostic process can be challenging. Thrombocytosis can be spurious, attributed to a reactive process or due to clonal disorder. This distinction is important as it carries implications for evaluation, prognosis, and treatment. Clonal thrombocytosis associated with the myeloproliferative neoplasms, especially essential thrombocythemia and polycythemia vera, carries a unique prognostic profile, with a markedly increased risk of thrombosis. This risk is the driving factor behind treatment strategies in these disorders. Clinical trials utilizing targeted therapies in thrombocytosis are ongoing with new therapeutic targets waiting to be explored. This paper will outline the mechanisms underlying thrombocytosis, the diagnostic evaluation of thrombocytosis, complications of thrombocytosis with a special focus on thrombotic risk as well as treatment options for clonal processes leading to thrombocytosis, including essential thrombocythemia and polycythemia vera.

Expression level and differential JAK2-V617F–binding of the adaptor protein Lnk regulates JAK2-mediated signals in myeloproliferative neoplasms

Activating mutations in signaling molecules, such as JAK2-V617F, have been associated with myeloproliferative neoplasms (MPNs). Mice lacking the inhibitory adaptor protein Lnk display deregulation of thrombopoietin/thrombopoietin receptor signaling pathways and exhibit similar myeloproliferative characteristics to those found in MPN patients, suggesting a role for Lnk in the molecular pathogenesis of these diseases. Here, we showed that LNK levels are up-regulated and correlate with an increase in the JAK2-V617F mutant allele burden in MPN patients. Using megakaryocytic cells, we demonstrated that Lnk expression is regulated by the TPO-signaling pathway, thus indicating an important negative control loop in these cells. Analysis of platelets derived from MPN patients and megakaryocytic cell lines showed that Lnk can interact with JAK2-WT and V617F through its SH2 domain, but also through an unrevealed JAK2-binding site within its N-terminal region. In addition, the presence of the V617F mutation causes a tighter association with Lnk. Finally, we found that the expression level of the Lnk protein can modulate JAK2-V617F–dependent cell proliferation and that its different domains contribute to the inhibition of multilineage and megakaryocytic progenitor cell growth in vitro. Together, our results indicate that changes in Lnk expression and JAK2-V617F–binding regulate JAK2-mediated signals in MPNs.

Clinicohematological study of thrombocytosis

OBJECTIVE

To find out etiology and clinical course of thrombocytosis in Indian pediatric population.

METHODS

A total of 250 patients having thrombocytosis (defined as platelet count >500 x 10(9)/L) on haematological investigations were studied over one yr period. All patients were evaluated clinically and were subjected to investigations, including complete blood counts (CBC) with peripheral smear examination. To elucidate the possible role of inflammatory cytokines in pathogenesis of RT, levels of Interleukin-6 (IL-6) and C - reactive protein (CRP) were estimated.

RESULTS

Infants and young children (<2 yr age) were most common group, contributing 60% of total cases. Out of total 250 cases, only 3 (1.2%) cases were found to have primary thrombocytosis and remaining 98.8% cases were having RT. Among RT patients, infections (alone or in association with iron deficiency anemia) were most common cause, accounting for 65% cases, while iron deficiency anemia (IDA) was second most common cause accounting for 41.3% cases (12.6% IDA alone and 28.7 % in association with infections). Other causes included nutritional dimorphic anemia and patients on treatment for megaloblastic anemia, acute lymphoblastic leukemia (during treatment) and lymphoma. Among various groups of RT, IL-6 and CRP levels were higher in patients with infection with or without IDA than IDA alone. One child with essential thrombocytosis and one child with RT had thrombotic complications. On follow up, platelet counts normalized in most of the patients with treatment of underlying conditions.

CONCLUSIONS

Results of this study suggest that essential thrombocytosis is extremely rare in children. Infections and IDA (alone or in association with infections) are common causes of RT. IL-6 and CRP levels are increased in patients with RT, to a higher level in patients with infections than in patients with IDA. Most patients with RT have uneventful recovery of platelet counts to normal range with treatment for underlying condition.

Thrombocytosis in neonates and young infants: a report of 25 patients with platelet counts of > or = 1000000 microl(-1)

OBJECTIVE

Thrombocytosis has been reported in neonates and young infants, but little is known of its prevalence, timing of onset, associated conditions, sequelae and outcomes. To better understand this condition, we used the data repositories of a multi-hospital health-care system to identify all individuals <or=140 days old (20 weeks) who, during the past 6 years, had a platelet count of >or=1000000 microl(-1).

STUDY DESIGN

We identified all infants with extreme thrombocytosis (using the Sutor definition of a platelet count of >or=1000000 microl(-1)) during the period of January 2003 through December 2008 in any Intermountain Healthcare facility. We obtained the information provided in this report from electronic and paper records.

RESULT

Among 40 471 infants who had one or more platelet counts performed in this period, 25 had extreme thrombocytosis. No cases were identified in the first week after birth, 40% were recognized between the second and fourth weeks and 40% between the fifth and eighth week. The prevalence of thrombocytosis had no relationship with birth weight or gestational age but a slight predominance of female patients (15/25) was noted. In all, 26 episodes were found among the 25 infants: 12 episodes involved an antecedent infectious disease, 8 had an antecedent surgical procedure, 4 had the anemia of prematurity and 1 each had congenital adrenal hyperplasia and opiate withdrawal syndrome. No pathological thromboses or hemorrhages or other sequelae were detected and all episodes resolved with no deaths.

CONCLUSION

The thrombocytosis cases that we report were all consistent with reactive thrombocytosis (also known as secondary thrombocytosis); none seemed to be essential (primary) thrombocytosis. We speculate that the pathogenesis involves increased platelet production due to megakaryopoietic stimulators induced by an infectious or inflammatory condition. From this series and previous reports, young infants with platelet counts up to 1300000 microl(-1) do not seem to have a significant risk of thrombotic or hemorrhagic problems, and do not generally require anti-platelet or cytoreductive treatment.

Elevated thrombopoietin in plasma of burned patients without and with sepsis enhances platelet activation

BACKGROUND

Thrombopoietin (TPO) is a humoral growth factor that does not induce platelet aggregation per se, but enhances platelet activation in response to several agonists. Circulating levels of TPO are increased in patients with sepsis and are mainly related to sepsis severity.

OBJECTIVES

To investigate the potential contribution of elevated TPO levels in platelet activation during burn injury complicated or not by sepsis.

METHODS

We studied 22 burned patients, 10 without and 12 with sepsis, and 10 healthy subjects. We measured plasma levels of TPO, as well as leukocyte-platelet binding and P-selectin expression. The priming activity of plasma from burned patients or healthy subjects on platelet aggregation and leukocyte-platelet binding, and the role of TPO in these effects were also studied in vitro.

RESULTS

Burned patients without and with sepsis showed higher circulating TPO levels and increased monocyte-platelet binding compared with healthy subjects. Moreover, TPO levels, monocyte-platelet binding and P-selectin expression were significantly higher in burned patients with sepsis than in burned patients without sepsis. In vitro, plasma from burned patients without and with sepsis, but not from healthy subjects, primed platelet aggregation, monocyte-platelet binding and platelet P-selectin expression. The effect of plasma from burned patients with sepsis was significantly higher than that of plasma from burned patients without sepsis. An inhibitor of TPO prevented the priming effect of plasma from burned patients.

CONCLUSIONS

Increased TPO levels may enhance platelet activation during burn injury and sepsis, potentially participating in the pathogenesis of multi-organ failure in these diseases.

Superoxide dismutase, copper and zinc concentrations in platelet-rich plasma of pneumonia patients

BACKGROUND

The aim of this study was to analyse platelet superoxide dismutase (SOD) activities (total SOD, manganese SOD and copper zinc SOD) and copper (Cu) and zinc (Zn) concentrations during the course of community-acquired pneumonia (CAP), and to compare them between patients with normal platelet count and those who have developed reactive thrombocytosis (RT).

METHODS

Platelet count, SOD activities and Cu and Zn concentrations in platelet-rich plasma were measured in patients with CAP on admission and at discharge.

RESULTS

Post-therapeutic platelet count increased significantly from the value recorded on admission. By the end of treatment, 42% of patients developed RT. All platelet SOD activities as well as Cu concentration were significantly lower in CAP patients than in control subjects. The initial Zn concentration was greater in CAP patients compared with controls and showed a decrease at discharge. On admission, there was no difference in all SOD activities between either subgroup with normal platelet count or subgroup with RT. At discharge all SOD activities were significantly lower in patients with RT. Also, catalytic activities of those enzymes were significantly lower in both subgroups in comparison with the initial values. Post-therapeutic Cu value was lower in patients with RT in comparison with patients having normal platelet count. Zn concentration decreased significantly at discharge when compared with the initial values only in patients with RT.

CONCLUSION

The pattern of changes might be indicative of a certain role of platelets in antioxidant response during treatment in CAP patients.

Effects of sepsis on neonatal thrombopoiesis

We serially evaluated the effects of sepsis and/or necrotizing enterocolitis (NEC) on neonatal thrombopoiesis, using a panel of tests that included platelet counts, thrombopoietin concentrations (Tpo), circulating megakaryocyte progenitor concentrations (CMPs), and reticulated platelets (RPs). Variables analyzed included sepsis type, time after onset of sepsis, platelet counts, and gestational (GA) and postconceptional ages (PCA). Twenty neonates were enrolled. Ten had Gram-negative, six had Gram-positive, and four had presumed sepsis. Four neonates had NEC stage II or higher, and six developed thrombocytopenia. Overall, septic neonates had significantly elevated Tpo concentrations and circulating megakaryocyte progenitors. The highest Tpo levels were associated with Gram-negative or presumed sepsis. RP percentages were increased only in neonates with low platelet counts, while RP counts (RP% x platelet count) were elevated in neonates with high platelet counts. Our findings suggest that septic neonates up-regulate Tpo production, leading to increased megakaryocytopoiesis and platelet release, although the degree of upregulation is moderate. The changes in RP% and RP count most likely reflect increased thrombopoiesis with variable degrees of platelet consumption. In addition, our findings suggest that different factors, likely including level of illness and/or specific platelet or bacterial products, can down-regulate the magnitude of the thrombopoietic response.

Gamma-Glutamyltransferase Activity and Total Antioxidant Status in Serum and Platelets of Patients with Community-acquired Pneumonia

BACKGROUND

We undertook this study to analyze serum and platelet gamma-glutamyltransferase (GGT) activity and total antioxidant status (TAS) concentration during the course of pneumonia and to compare them between patients with normal platelet count and those who developed reactive thrombocytosis.

METHODS

Platelet count, GGT activity and TAS concentration in serum (S) and platelet (Plt) isolates were measured in 60 patients with community-acquired pneumonia (CAP) on admission and at discharge.

RESULTS

At the end of treatment, platelet count increased significantly from the value recorded on admission. By the end of treatment, 42% of patients developed reactive thrombocytosis. Serum and platelet GGT activity was higher, whereas (S)TAS was significantly lower in CAP patients than in control subjects. On admission, (Plt)TAS was significantly higher in CAP patients as compared with control subjects; at discharge, (Plt)TAS was lower in comparison with either patient admission and control subjects. GGT activity and TAS concentration in serum and platelet isolate on admission did not differ significantly between patients with and without thrombocytosis. At discharge, (S)GGT activity showed no significant changes, whereas (Plt)GGT decreased significantly in patients with thrombocytosis as compared with those without thrombocytosis. In patients with thrombocytosis, (S)TAS concentration showed no significant difference, whereas (Plt)TAS concentration measured at discharge was significantly lower in patients with thrombocytosis as compared to those with normal platelet count.

CONCLUSIONS

The pattern of changes in (Plt)GGT catalytic activity and TAS concentration might be indicative of a certain role of thrombocytosis during treatment in patients with CAP. Further investigations are necessary to clarify these changes.

High Thrombopoietin Concentrations in The Cerebrospinal Fluid of Neonates with Sepsis And Intraventricular Hemorrhage May Contribute to Brain Damage

Thrombopoietin (TPO) and its receptor (TPOR) are expressed in the central nervous system (CNS). Although TPO shares significant homology with various neurotrophins, recent data indicate a proapoptotic function of TPO in the CNS. In this study, TPO concentrations were analyzed in the cerebrospinal fluid (CSF) of neonates. Human neuroblastoma-derived SH-SY5Y cells were established to elucidate the effects of inflammation and hypoxia on neuronal Tpo expression. TPO was detectable in the CSF of 6 of 15 neonates with bacterial infection/sepsis (median 140, range 2-613 pg/mL), 5 of 9 neonates with posthemorrhagic hydrocephalus (median 31, range 1.4-469 pg/mL), 3 of 4 neonates with posthemorrhagic hydrocephalus plus bacterial infection/sepsis or meningitis (median 97, range 6-397 pg/mL), but not in controls ( n = 3). Neither the presence of detectable TPO nor its level in the CSF significantly correlated with any clinical or laboratory parameter. In SH-SY5Y cells, TPO and TPOR expression was detected by RT-PCR and Western blot analysis. In vitro, interleukin-6 (IL-6) did not significantly change Tpo gene expression. In contrast, Tpo mRNA expression significantly decreased under hypoxia, whereas erythropoietin (EPO) mRNA expression increased. In conclusion, our data provide evidence that in neuronal cells, TPO production is regulated by different mechanisms than in hepatocytes.

Neutrophil alkaline phosphatase activity in respiratory viral infection

Neutrophil alkaline phosphatase (NAP) is used as a diagnostic marker in several hematological disorders. In regard to the role of NAP in infectious diseases, previous investigators have presented the hypothesis that NAP activity is useful to distinguish viral infections from bacterial infections. Because the numbers of patients enrolled in previous studies of viral infections were limited, we intended to evaluate the hypothesis by measuring NAP activity in a large number of pediatric patients with respiratory viral infections. A cytochemical analysis of NAP was performed in 160 patients with various types of respiratory infections. In patients with adenovirus or respiratory syncytial (RS) virus infection, NAP activity was significantly higher than the control value newly established at our department, while in patients with Epstein-Barr virus, measles, or influenza infection, it was comparable to the control value. On an individual basis, NAP scores (determined from NAP cytochemical activity) in 22 of 26 patients (84.6%) with adenovirus infection, and 31 of 42 patients (73.8%) with RS virus infection were found to exceed the 95% confidence upper limit of the control group. In conclusion, NAP activity is quite varied among different respiratory viral infections. When NAP activity is high in respiratory infections, adenovirus or RS virus infection, as well as bacterial infections, should be taken into consideration.

Value of platelet count in the prognosis of patients with pyogenic liver abscess

AIM: To study the relationship between platelet count and the prognosis of patients with pyogenic liver abscess.

METHODS: A total of patients with pyogenic liver abscess were diagnosed by computed tomography (CT), magnetic resonance imaging (MRI) and liver punctures, and the average focus size was 6.54 cm in diameter. Blood routine examination was performed everyday, combined with B-ultrasonography every three days. The relationship between the dynamic changes of platelet count and the prognosis of pyogenic liver abscess patients was analyzed.

RESULTS: Within one week, 43 (38.39%) patients were found with maximal platelet count more than or equal to 400 × 10⁹/L, and 22 patients (19.64%) with platelet count less than 400 × 10⁹/L. More than one week, 29 patients (25.89%) were with maximal platelet count more than or equal to 400 × 10⁹/L, 18 patients (16.07%) with platelet count less than 400 × 10⁹/L. Thrombocytosis occurred quickly in the patients in hospital less than one week, whose maximal platelet count was more than or equal to 400 × 10⁹/L, and their clinical symptoms were improved remarkably as compared with those of patients in hospital more than one week, with maximal platelet count less than 400 × 10⁹/L (P < 0.05).

CONCLUSION: Pyogenic liver abscess patients, in whom thrombocytosis occurs in short time, have a favorable prognosis. Blood count is an important indicator for the prognosis of Pyogenic liver abscess.

Thrombocytosis in Pediatric Patients Is Associated with Severe Lower Respiratory Tract Inflammation

BACKGROUND

Secondary thrombocytosis is associated with a variety of clinical conditions. The aim of this study was to determine the incidence and to analyze the clinical significance and prognostic value of thrombocytosis in lower respiratory tract infection.

METHODS

A total of 102 pediatric patients were hospitalized with lower respiratory tract infection during a period of 30 months.

RESULTS

Forty nine (48%) of those patients had platelet counts >500 x 10(9)/L. The median age of the thrombocytotic patients was 31 months as opposed to 61 months for the non-thrombocytotic ones. The patients with thrombocytosis had more serious illness. This is indicated by three factors: more severe clinical condition on admission, presence of respiratory distress and longer hospitalization. Sedimentation rate >70 mm/h was observed in 44.4% patients of the thrombocytotic group compared to only 27.7% of the non-thrombocytotic ones. Almost all patients with pleural effusion were thrombocytotic. The children with very high platelet counts >650 x 10(9)/L presented with respiratory distress on admission and required longer hospitalization time. No other significant clinical or laboratory differences were demonstrated between these patients and the remainder of the thrombocytotic patients.

CONCLUSIONS

Thrombocytosis is a common finding among patients with lower respiratory tract infection. Thrombocytotic patients have a more severe clinical condition. Importantly, thrombocytosis occurs almost exclusively in patients with pleural effusion. The platelet count may be a useful clinical marker associated with the severity of the lower respiratory tract infection.

Thrombopoietin production in wild-type and interleukin-6 knockout mice with acute inflammation

Clinical and laboratory studies indicate that thrombopoietin (TPO) gene expression increases during inflammation. To clarify the role of interleukin 6 (IL-6) in this process, blood cell counts, plasma TPO concentrations, and hepatic and renal TPO mRNA levels were investigated in wild-type and IL-6 knockout mice, with sterile abscesses produced by subcutaneous injection of turpentine oil. Treatment did not cause a change in blood cell counts during the 72 h period of observation. The numbers of thrombocytes and erythrocytes were slightly lower in the IL-6 knockout mice than in the wild-type littermates under all conditions. Plasma IL-6 and TPO concentrations increased on turpentine injection only in the wild-type mice. In addition, turpentine treatment of these caused an increase in hepatic TPO mRNA levels as assessed by competitive polymerase chain reaction (RT-PCR) and real-time PCR, whereas renal TPO mRNA levels were unaltered. TPO mRNA levels did not increase in the livers of IL-6 knockout mice on turpentine treatment. These results support the concept that TPO behaves like an acute-phase protein in that its synthesis is induced by IL-6 in the liver.

Primary and secondary thrombocytosis in childhood

This review summarizes current data on the pathomechanisms and clinical aspects of primary and secondary thrombocytosis in childhood. Primary thrombocytosis is extremely rare in childhood, mostly diagnosed at the beginning of the second decade of life. As in adults, the criteria of the Polycythemia Vera Group are appropriate to diagnose primary thrombocytosis. The pathomechansims of non-familial forms are complex and include spontaneous formation of megakaryopoietic progenitors and increased sensitivity to thrombopoietin (Tpo). Familial forms can be caused by mutations in Tpo or Tpo receptor (c-mpl) genes. These mutations result in overexpression of Tpo, sustained intracellular signalling or disturbed regulation of circulating Tpo. Treatment of primary thrombocytosis is not recommended if platelet counts are <1500/nl and bleeding or thrombosis did not occur in patient's history. In severe cases, decision on treatment should weigh potential risks of treatment options (hydroxyurea, anagrelide) against expected benefits for preventing thrombosis or haemorrhage. Secondary thrombocytosis is frequent in children, in particular in the first decade of life. Hepatic Tpo production is stimulated in acute response reaction to a variety of disorders. Thrombosis prophylaxis is not required, even at platelet counts >1000/nl, except for cases with additional prothrombotic risk factors.

Thrombopoietin in the Cerebrospinal Fluid of Patients with Aseptic and Bacterial Meningitis

Despite the recent evidence of the localization of thrombopoietin (TPO) and its receptor in the central nervous system (CNS), TPO protein concentrations in the cerebrospinal fluid (CSF) remained to be clarified. We previously reported that serum TPO is increased in children with meningitis. To determine changes in TPO concentrations in the CSF by meningitis and to explore the relationship between serum and CSF TPO concentrations, we measured TPO concentrations in 110 CSF samples and 33 serum/CSF pairs from 11 bacterial meningitis, 49 aseptic meningitis, and 50 nonmeningitis children. In only 12% (13 of 110) of CSF samples (0 bacterial meningitis, 8 aseptic meningitis, and 5 controls), TPO concentrations could be determined (24.1 +/- 29.0 pg/ml). CSF TPO concentrations did not significantly differ among the three groups and did not correlate with age. TPO concentrations in all serum samples were detectable, and mean concentrations in bacterial meningitis (510.6 +/- 237.0 pg/ml) were significantly higher than those in aseptic meningitis (136.6 +/- 71.6, p < 0.01) and controls (181.3 +/- 88.3, p < 0.01). These findings suggest that TPO is not produced in the CNS of patients with meningitis and that TPO did not cross the blood-brain barrier even during meningeal infection.

Thrombopoietin and Interleukin-6 in Children with Pneumonia-Associated Thrombocytosis

BACKGROUND

The aim of this study was to investigate why some, but not all, children develop thrombocytosis during the course of pneumonia.

METHODS

The retrospective study included 40 healthy children and 75 children with pneumonia: 17 patients with platelet count within the reference values, i.e., platelet count </=450 x 10(9)/L, and 58 with thrombocytosis >450 x 10(9)/L. Erythrocyte sedimentation rate, leukocyte and platelet counts, and concentrations of hemoglobin, C-reactive protein, interleukin-6 and thrombopoietin were determined in the blood of patients and control groups of children.

RESULTS

Patients with thrombocytosis were slightly younger (3.0 +/- 1.8 years and median 2.5 years, respectively) than patients with normal platelet count (3.8 +/- 2.4 years and median 4 years, respectively). Additionally, according to clinical and radiological findings, pneumonia in children with thrombocytosis had a more severe and protracted course. Serum thrombopoietin concentrations were found to be 91.2 +/- 41.7 ng/L (range: 14.3-166.7 ng/L) in patients with normal platelet count (313 +/- 70 x 10(9)/L, range: 206-428 x 10(9)/L). In patients with thrombocytosis (581 +/- 131 x 10(9)/L, range: 450-830 x 10(9)/L) serum thrombopoietin ranged from 63.6 to 1115.9 ng/L (526.6 +/- 268.4 ng/L). In these patients both concentration of hemoglobin (114 +/- 12 g/L) and iron (4.3 +/- 1.3 micromol/L) significantly decreased as compared with the control group.

CONCLUSIONS

Study results suggested the possible development of reactive thrombocytosis in children with pneumonia. As platelets are involved in inflammatory reaction, reactive thrombocytosis might be part of the mechanism of defense. Reactive thrombocytosis may develop as a sequel of either anemia or inflammatory reaction (or both).

An unusual case of thrombocytosis associated with concurrent cytomegalovirus and respiratory syncytial virus infection in an immunocompetent infant: possible roles of thrombopoietin and interleukin-6

This is the case study of concurrent cytomegalovirus and respiratory syncytial virus infection in an infant who showed thrombocytosis, liver dysfunction and bronchiolitis. The combination of thrombocytosis with this co-infection is causally related to elevated levels of thrombopoietin and interleukin-6. This study represents the first such case ever recorded.

Sepsis severity is the major determinant of circulating thrombopoietin levels in septic patients

OBJECTIVE

To measure serum thrombopoietin levels and to investigate their relationship with platelet counts and other potential determinants in septic patients.

DESIGN

Prospective study comparing septic patients and healthy volunteers.

SETTING

General intensive care units in two tertiary university hospitals.

PATIENTS

A total of 152 consecutive septic patients (69 with sepsis, 24 with severe sepsis, and 59 with septic shock). Twenty-two healthy volunteers served as control subjects. Sepsis severity was determined by grading septic patients in those having sepsis, severe sepsis, and septic shock.

INTERVENTIONS

None.

MEASUREMENTS AND MAIN RESULTS

After blood sampling, platelet counts, and serum thrombopoietin, interleukin-6 and C-reactive protein levels were measured. Platelets did not decrease in patients with sepsis, but they significantly decreased in patients with severe sepsis and septic shock (p <.01 vs. controls and sepsis). In contrast, thrombopoietin levels (median [range]) increased in patients with sepsis (159 [34-1272] pg/mL) compared with controls (57 [33-333] pg/mL, p <.001), exhibiting further significant increase in patients with severe sepsis and septic shock (461 [73-1550] and 522 [45-2313] pg/mL, respectively, p <.001 vs. sepsis). In multiple regression analysis, thrombopoietin levels were independently related only to sepsis severity (higher in patients with increased sepsis severity, p <.001) and platelet counts (higher in patients with lower platelet counts, p =.004). Sepsis severity accounted for most of the variance explained by the model. Thrombopoietin was significantly related to interleukin-6 (r =.26) and C-reactive protein (r =.37, p <.001 for both). In serial measurements, interleukin-6 peak values constantly preceded those of thrombopoietin, whereas peaks in thrombopoietin levels coincided with clinical episodes of septic shock.

CONCLUSIONS

Sepsis severity is the major determinant of elevated thrombopoietin levels in septic patients, whereas platelet count is a secondary determinant. Thrombopoietin represents a potential marker of sepsis severity.

Age-dependent changes in the incidence and etiology of childhood thrombocytosis

To determine the incidence and etiology of childhood thrombocytosis, over 15,000 platelet counts in 7,539 patients performed at a single regional hospital were reviewed. When thrombocytosis was defined as > or =500 x 10(9)/l of platelet counts, the condition could be diagnosed in 6.0% (456 cases) of the patients. All patients were classified as having secondary thrombocytosis. The incidence of thrombocytosis dramatically changed throughout child development; it was 12.5% in neonates, peaked to 35.8% in 1-month-old infants and then returned to 12.9% in 6- to 11-month-old infants. Thereafter, it gradually decreased with age to only 0.6% in 11- to 15-year-old children. Frequent causes of thrombocytosis included infection (67.5%), Kawasaki disease (9.4%), prematurity (7.7%) and iron deficiency anemia (6.4%). Thrombocytosis was an incidental finding in a substantial population of early infants. Thrombocytosis as a reaction to several types of infection and Kawasaki disease was more common in children under 7 years old, while autoimmune disease and tissue damage were major causes in children aged 11-15 years. No child had thromboembolic complications. These findings indicate that childhood thrombocytosis is a benign condition and its incidence and etiology seem to depend on age.

Thrombopoietin in acute liver failure

Thrombopoietin (TPO) is the primary regulator of platelet production. TPO is produced in the liver and levels are low in patients with cirrhosis. Because thrombocytopenia is common in patients with acute liver failure (ALF), we measured TPO concentrations (normal TPO range, 31 to 136 pg/mL) in 51 patients with ALF to determine if low levels were associated with thrombocytopenia. TPO levels from hospital day 2 were elevated in 43% of patients, normal in 47%, and decreased in 10% of patients. Levels were higher in acetaminophen-induced than in non-acetaminophen-induced ALF, 160 (12 to 549) pg/mL versus 73 (18 to 563) pg/mL, respectively, P =.031. TPO levels did not correlate with platelet count and were not related with survival or infection. We analyzed daily TPO levels for the first week of hospitalization in 12 patients with acetaminophen-induced ALF and observed a gradual increase from a median admission level of 50 (5 to 339) pg/mL to a median peak level of 406 (125 to 1,081) pg/mL occurring on day 5 (3 to 6). Platelets were reduced in 11 of the 12 patients with a nadir platelet count of 52 (19 to 156) x 10(9) cells/L occurring on day 5.5 (1 to 6). The peak TPO level did not correlate with the nadir platelet count (P =.43). In conclusion, the normal inverse relationship between platelet count and TPO levels was not observed in ALF. Despite severe hepatic dysfunction, serum TPO levels were initially normal and increased during hospitalization in acetaminophen-induced ALF, but did not prevent the development of thrombocytopenia.