Neonatal transfusion practice.

Many previously widely accepted neonatal transfusion practices are changing as neonatologists become more aware of the risks to their patients of multiple blood product transfusions. Recent literature and research on neonatal transfusion practice are here reviewed, and practical guidelines and trigger thresholds for blood products commonly used in neonatal medicine are proposed.

Neonatal thrombocytopenia: causes and management.

Neonatal thrombocytopenia is a common clinical problem. Thrombocytopenia presenting in the first 72 hours of life is usually secondary to placental insufficiency and caused by reduced platelet production; fortunately most episodes are mild or moderate and resolve spontaneously. Thrombocytopenia presenting after 72 hours of age is usually secondary to sepsis or necrotising enterocolitis and is usually more severe and prolonged. Platelet transfusion remains the only treatment. There is a need for trials to define the safe lower limit for platelet count and which neonates will benefit from treatment.

Evaluation and treatment of thrombocytopenia in the neonatal intensive care unit.

UNLABELLED: Phlebotomy-induced anaemia excepted, thrombocytopenia is the most common haematological abnormality in neonatal intensive care unit (NICU) patients. Roughly one-quarter of all NICU patients and half of all sick preterm neonates develop thrombocytopenia. Whereas a large number of varied precipitating conditions has been identified, early-onset thrombocytopenia (<72 h) is most commonly associated with fetomaternal conditions complicated by placental insufficiency and/or fetal hypoxia, e.g. maternal pre-eclampsia and fetal intrauterine growth restriction. The resulting neonatal thrombocytopenia is usually mild to moderate, resolves spontaneously and requires no specific therapy. Deviation from this pattern of thrombocytopenia suggests the presence of more significant precipitating conditions. The most important of these are the immune thrombocytopenias, and every NICU should develop investigation and treatment protocols to manage these cases promptly and avoid unnecessary risk of haemorrhage. In contrast, late-onset thrombocytopenia (>72 h) is almost always associated with sepsis or necrotizing enterocolitis and the associated thrombocytopenia is severe, prolonged and often requires treatment by platelet transfusion. Unfortunately, evidence-based guidelines for platelet transfusion therapy in NICU patients are currently unavailable, making it difficult to define widely accepted thresholds for transfusion and leading to a significant variation in transfusion practice between centres. CONCLUSION: While improving this situation remains a pressing need, the growing evidence that impaired megakaryocytopoiesis and platelet production are major contributors to many neonatal thrombocytopenias suggests that recombinant haemopoietic growth factors, including thrombopoietin and interleukin-11, may be useful future therapies to ameliorate neonatal thrombocytopenia.

Platelet transfusion in the management of severe thrombocytopenia in neonatal intensive care unit patients.

Platelet transfusions are frequently given to neonatal intensive care unit (NICU) patients with severe thrombocytopenia (platelets less than 50 x 10(9) L(-1)) but no study has assessed whether this is clinically appropriate. To address this we conducted a retrospective review of platelet transfusion practice in patients developing severe thrombocytopenia over 3 years in a single NICU. Out of 901 admissions, 53 (6%) developed severe thrombocytopenia. Twenty-seven neonates received a total of 63 platelet transfusions, the main triggers being: platelet count less than 30 x 10(9) L(-1) (all patients), or less than 50 x 10(9) L(-1) in those with previous haemorrhage or clinical instability. No major haemorrhage occurred during severe thrombocytopenia either in neonates in whom platelet transfusions were withheld (26/53) or in neonates given platelets who survived to discharge (22/27). Five preterm neonates given platelets died but all had overwhelming sepsis or necrotizing enterocolitis and none died directly as a result of haemorrhage. Although the widely used liberal triggers for neonatal platelet transfusion highlighted in this review reflect available guidelines, and represent cautious ('safe') haemostatic practice, they are likely to result in unnecessary transfusion for a significant number of NICU patients. Improved practice requires definition of a safe lower limit for platelet count in stable neonates; effective platelet transfusion strategies for sick neonates; and improved therapies for conditions precipitating severe thrombocytopenia.

Neonatal thrombocytopenia: new insights into pathogenesis and implications for clinical management.

The healthy fetus has a platelet count of greater than 150 x 10(9)/L by the second trimester of pregnancy and only 2% of term infants are thrombocytopenic at birth. Severe thrombocytopenia (platelets < 50 x 10(9)/L) occurs in fewer than three per 1000 term infants, the most important cause being alloimmune thrombocytopenia. In contrast, in infants admitted to neonatal intensive care units, thrombocytopenia develops in 25% and in up to half of sick preterm infants. Recent evidence shows that these infants mostly have evidence of underlying impaired fetal megakaryocytopoiesis and platelet production following pregnancy complications characterized by placental insufficiency or fetal hypoxia. The mechanism of this is unknown. However, many neonatal complications exacerbate this thrombocytopenic potential and 20% of thrombocytopenias in neonatal intensive care unit patients are severe. Evidence-based guidelines for platelet transfusion therapy in these patients are yet to be defined, but as platelet underproduction underlies most neonatal thrombocytopenias, recombinant hemopoietic growth factors, including thrombopoietin and interkeukin-11, may be useful future therapies.

Thrombopoietin in the fetus and neonate.

C-mpl ligand or thrombopoietin (Tpo) is increasingly recognised as the major regulator of platelet homeostasis in humans. Relatively little is known about Tpo in the fetus and neonate but no evidence has yet been found to suggest any fundamental difference in Tpo structure, function and regulation in the fetus and neonate compared to older age groups. Tpo mRNA transcripts have been detected in the fetus as early as 6 weeks post conception and the liver appears to be the main site of Tpo production in both the fetus and neonate. The vast majority of healthy newborns have detectable levels of circulating Tpo and raised Tpo levels are commonly, but not consistently, found in thrombocytopenic neonates. In adults receptor binding and subsequent metabolism of Tpo is proposed as the main method of regulation of the circulating Tpo level. Preliminary studies in neonates showing increased Tpo levels most often during thrombocytopenia accompanied by reduced megakaryocytopoiesis supports this concept. In addition to this demonstrable fetal and neonatal endogenous Tpo production megakaryocyte progenitor and precursor cells from the fetus and from preterm and term newborns proliferate and differentiate extensively in-vitro in response to exogenous Tpo. Furthermore a recent study has shown a marked rise in platelet count in newborn rhesus monkeys administered one form of recombinant Tpo. Although these studies remain at an early stage together these findings strongly suggest that, as in adults, Tpo is the major regulator of platelet homeostasis in the fetus and neonate. Thrombocytopenia is common in sick neonates and progress in understanding this important clinical problem is likely to be greatly enhanced by the current and future research into Tpo production, function and regulation in the healthy and thrombocytopenic fetus and neonate.

Thrombopoietin has a primary role in the regulation of platelet production in preterm babies.

Thrombocytopenia in the first days of life, in association with evidence of reduced megakaryocytopoiesis and platelet production at birth, is common in sick preterm babies. Thrombopoietin (Tpo) is the major regulator of platelet production in adults. However, these babies have low Tpo levels at birth, suggesting that the Tpo response to thrombocytopenia may be impaired. To test this hypothesis we 1) measured Tpo levels, 2) measured circulating megakaryocyte progenitors serially over the first 12 d of life in 13 preterm babies with early onset thrombocytopenia and in 14 control babies with evidence of normal megakaryocytopoiesis, and 3) measured Tpo levels in thrombocytopenic children (n = 13). In control babies, platelet counts and progenitor numbers remained normal and Tpo levels were consistently low-d 1:160+/-23 pg/mL (mean+/-SEM), d 4/5: 154+/-18 pg/mL and d 12: 150+/-58 pg/mL. In thrombocytopenic babies, platelet counts and megakaryocyte progenitor numbers were significantly lower than controls at d 1: platelets 130+/-14 x 10(9)/L versus 255+/-20 x 10(9)/L (p < 0.001) and megakaryocyte progenitors 552 versus 3907 colonies/mL (mean, p < 0.001), and fell further to nadir on d 4/5: platelets 76+/-6 X 10(9)/L versus 259+/-21 x 10(9)/L (p < 0.001) and MK progenitors 479 versus 2742 colonies/mL (p < 0.05). Tpo levels were only slightly raised on d 1:247+/-52 pg/mL (p = 0.24), but then rose sharply by d 4/5: 425+/-75 pg/mL (p < 0.001). By d 12, platelet count, megakaryocyte progenitors and Tpo level (145+/-29 pg/mL) had returned to control levels. Tpo levels at platelet nadir in thrombocytopenic babies were significantly lower than in thrombocytopenic children: mean 425 versus 1383 pg/mL (p < 0.001). These data show that Tpo is important in platelet homeostasis in preterm babies, with a close reciprocal relationship with platelet count and progenitor numbers during thrombocytopenia. However, the increase in Tpo levels seen in these babies was modest, despite significantly impaired megakaryocytopoiesis, and when compared with that seen in children with thrombocytopenia. This offers further evidence that preterm babies have an impaired Tpo response to thrombocytopenia and suggests that recombinant human Tpo may have a role in the prevention/treatment of preterm thrombocytopenia.

Inhibition of erythroid progenitor cells by anti-Kell antibodies in fetal alloimmune anemia.

BACKGROUND: In alloimmune anemia of the newborn, the level of hemolysis caused by the presence of antibodies to antigens of the Kell blood-group system is less than that caused by antibodies to the D antigen of the Rh blood-group system, and the numbers of reticulocytes and normoblasts in the baby's circulation are inappropriately low for the degree of anemia. These findings suggest that sensitization to Kell antigens results in suppression of fetal erythropoiesis as well as hemolysis. METHODS: We compared the growth in vitro of Kell-positive and Kell-negative hematopoietic progenitor cells from cord blood in the presence of human monoclonal anti-Kell antibodies and anti-D antibodies and serum from women with anti-Kell antibodies. RESULTS: The growth of Kell-positive erythroid progenitor cells (erythroid burst-forming units and colony-forming units) from cord blood was markedly inhibited by monoclonal IgG and IgM anti-Kell antibodies in a dose-dependent fashion (range of concentrations, 0.2 to 20 percent), but monoclonal anti-D antibodies had no effect. The growth of these types of cells from Kell-negative cord blood was not affected by either type of antibody. Neither monoclonal anti-Kell antibodies nor monoclonal anti-D antibodies inhibited the growth of granulocyte or megakaryocyte progenitor cells from cord blood. Serum from 22 women with anti-Kell antibodies inhibited the growth of Kell-positive erythroid burst-forming units and colony-forming units but not of Kell-negative erythroid burst-forming units and colony-forming units (P<0.001 for the difference between groups). The maternal anti-Kell antibodies had no inhibitory effects on granulocyte-macrophage or mega-karyocyte progenitor cells from cord blood. CONCLUSIONS: Anti-Kell antibodies specifically inhibit the growth of Kell-positive erythroid burst-forming units and colony-forming units, a finding that supports the hypothesis that these antibodies cause fetal anemia by suppressing erythropoiesis at the progenitor-cell level.

Endogenous thrombopoietin levels and effect of recombinant human thrombopoietin on megakaryocyte precursors in term and preterm babies.

Thrombocytopenia (platelets <150 x 10[9]/L) is common in the early newborn period. Recent evidence suggests this is due mainly to impaired fetal megakaryocytopoiesis/platelet production. The cause remains unknown. Thrombopoietin (Tpo) is now recognized as the major regulator of platelet production in adults. However, nothing is known about Tpo levels, or the role of Tpo in megakaryocytopoiesis/platelet production, in the fetus/newborn. To answer these questions we: 1) measured plasma Tpo levels by ELISA at birth in healthy term (n = 17) and preterm (gestational age, 24-34 wk) babies (n = 16), and in thrombocytopenic preterm babies (n = 13); and 2) assessed the in vitro Tpo dose response characteristics of circulating megakaryocyte precursor cells (MKp) from all three groups. The median Tpo levels were similar in term babies 145 pg/mL (range 52-237 pg/mL) compared with preterm babies 132 pg/mL (32-318 pg/mL). In the thrombocytopenic preterm babies the median Tpo level of 185 (46-264) was not significantly higher than in healthy babies, despite the fact that their median platelet counts were significantly lower--82 x 10(9)/L (range 21-135), compared with the healthy preterm babies 252 x 109/L (152-320)--p < 0.0001. Tpo levels in the thrombocytopenic preterm babies were also much lower than levels measured in three thrombocytopenic children (905, 2138, and 2700 pg/mL). MKp from all three groups showed dose-dependent proliferation in response to Tpo (p < 0.01 at 100 ng/mL Tpo). Increases in MKp were greater in healthy and thrombocytopenic preterm babies when compared with term babies: 48.2-, 24.6-, and 9.8-fold, respectively (p < 0.05 for both comparisons). These results strongly suggest that: 1) Tpo is a major regulator of megakaryocytopoiesis/platelet production in the fetus/newborn, 2) impaired fetal Tpo production may be a factor in early thrombocytopenia in preterm babies, and 3) recombinant human Tpo is likely to be effective in the treatment of early neonatal thrombocytopenia.

Circulating megakaryocytes and their progenitors in early thrombocytopenia in preterm neonates.

Thrombocytopenia is common in sick preterm babies. Despite this, platelet production in thrombocytopenic preterm babies has rarely been assessed. To address this problem we have developed miniaturized assays to study circulating megakaryocyte (MK) progenitors [burst-forming unit (BFU)-MK and colony-forming unit (CFU)-MK], total cultured MK precursors and mature MK, by culturing mononuclear cells purified from 0.5-1 mL of preterm peripheral blood. MK lineage colonies and cells are identified by an anti-IIb/IIIa antibody (CD61). We prospectively studied circulating BFU-MK/CFU-MK, total cultured MK precursors and mature MK in 63 preterm babies (gestational age 24-34 wk). Twenty-six developed early thrombocytopenia (platelets < 150 x 10(9)/L by 48 h), whereas the remaining 37 babies maintained normal platelet counts. Twenty-one of the 26 thrombocytopenic babies were born to mothers with pregnancy-induced hypertension or were growth retarded. At birth, thrombocytopenic babies had severely reduced numbers of all MK precursors compared with nonthrombocytopenic babies: BFU-MK 82 +/- 50 versus 663 +/- 174 colonies/mL, mean +/- SEM; CFU-MK 596 +/- 196 versus 3267 +/- 530 colonies/mL; total MK precursors 97 +/- 30 versus 301 +/- 49 x 10(3) cells/mL and mature MK 8 +/- 2 versus 37 +/- 8 x 10(3) cells/mL, respectively. Thrombocytopenia resolved by d 10 in all babies accompanied or preceded by a recovery to normal numbers of circulating MK progenitors. Eighteen (69%) of the thrombocytopenic babies were also neutropenic (neutrophils < 2 x 10(9)/L); in these babies neutrophil progenitor cells (CFU-granulocyte/monocyte) were also severely reduced compared with the nonthrombocytopenic babies (539 +/- 280 versus 1937 +/- 348 colonies/mL, mean +/- SEM). This indicates that the principal cause of the thrombocytopenia and neutropenia is reduced platelet and neutrophil production occurring as a consequence of reduced numbers of MK and CFU-granulocyte/monocyte progenitors, respectively. Taken together these data suggest the hematologic abnormalities characteristic of newborns born to mothers with pregnancy-induced hypertension or with intrauterine growth retardation are a consequence of dysregulation of fetal hemopoiesis occurring proximal to committed MK and neutrophil progenitors, most likely at the level of the primitive multipotent hemopoietic stem cell.

Circulating megakaryocytes and their progenitors (BFU-MK and CFU-MK) in term and pre-term neonates.

Thrombocytopenia is a common occurrence in sick newborn babies. Despite this, platelet production in the newborn has rarely been assessed, principally because of the difficulties of obtaining bone marrow, especially on a serial basis. We have developed two miniaturized assay systems to study megakaryocyte (MK) progenitor cell differentiation, from BFU-MK and CFU-MK to mature MK, by culturing mononuclear cells purified from 0.5-1 ml of neonatal peripheral blood. BFU-MK and CFU-MK were assayed in agar, whilst total cultured MK precursors and mature MK were assessed in liquid culture. In both systems, MK lineage cells were identified morphologically and by an anti-IIb/IIIa antibody (CD61). Normal ranges for MK precursors in term neonates were established from cord blood studies of 40 healthy term babies and compared with cord blood studies in 16 non-thrombocytopenic pre-term babies (gestational age range 24-36 weeks). Pre-term babies had greater numbers of all MK precursors than term babies: BFU-MK 414 +/- 61 v 151 +/- 18 colonies/ml (mean +/- SEM); CFU-MK 2444 +/- 337 v 869 +/- 64 colonies/ml; total MK precursors 213 +/- 36 v 54 +/- 6 x 10(3) cells/ml and mature MK 20 +/- 4 v 7 +/- 1 x 10(3) cells/ml. In addition, in newborn babies (n = 22), with no evidence of platelet consumption, circulating MK progenitor numbers at birth correlated with platelet numbers. These data indicate that in the newborn the measurement of circulating MK precursors provides a good indicator of megakaryocytopoiesis, and hence platelet production, and therefore is a useful and practical way of investigating neonatal thrombocytopenia.

Fetal marrow suppression after maternal chemotherapy for leukaemia.

A preterm baby, whose mother received chemotherapy for acute leukaemia during pregnancy, required intensive care because of profound anaemia and neutropenia. Haemopoietic progenitor cell studies showed fetal marrow suppression. Those caring for such mothers and babies should know the possible serious effects chemotherapy for malignancies can have on a developing fetus. Long term follow up of the baby is imperative.