Circulating erythroid progenitors in the anemia of prematurity

Anemia in the preterm infant: erythropoietin versus erythrocyte transfusion--it's not that simple

Since the late 1980s recombinant human erythropoietin (r-EPO) has been studied as an alternative to packed red blood cell (RBC) transfusion for the treatment of anemia of prematurity in very low birth weight infants. Initial trials and reports focused on r-EPO's ability to prevent or treat anemia of prematurity with the goal of eliminating RBC transfusion but achieved limited success. New concerns about the safety of r-EPO administration have emerged. Past cost-benefit analyses of r-EPO administration versus transfusion for the treatment of anemia of prematurity have been nearly balanced. Autologous transfusion, blood-sparing technologies, changes in RBC transfusion technique and safety, and further elucidation of the risk-benefit ratio of r-EPO therapy may change the cost-benefit analysis.

Anemia in the preterm infant: erythropoietin versus erythrocyte transfusion--it's not that simple

Since the late 1980s recombinant human erythropoietin (r-EPO) has been studied as an alternative to packed red blood cell (RBC) transfusion for the treatment of anemia of prematurity in very low birth weight infants. Initial trials and reports focused on r-EPO's ability to prevent or treat anemia of prematurity with the goal of eliminating RBC transfusion but achieved limited success. New concerns about the safety of r-EPO administration have emerged. Past cost-benefit analyses of r-EPO administration versus transfusion for the treatment of anemia of prematurity have been nearly balanced. Autologous transfusion, blood-sparing technologies, changes in RBC transfusion technique and safety, and further elucidation of the risk-benefit ratio of r-EPO therapy may change the cost-benefit analysis.

Erythropoietin pharmacokinetic/pharmacodynamic analysis suggests higher doses in treating neonatal anemia

BACKGROUND

The establishment of effective treatment of neonatal anemia using recombinant human erythropoietin (r-HuEPO) requires a thorough understanding of the physiology and mechanism of EPO's pharmacologic effect. The purpose of the present preclinical study in sheep was to elucidate the stimulatory effect of EPO on erythroid progenitors and their differentiation into reticulocytes useful in predicting optimal r-HuEPO dosing.

METHODS

Five young adult sheep each underwent two phlebotomies spaced 4-6 weeks apart in which their hemoglobin levels were reduced from 12 g/dL to 3-4 g/dL. Endogenous EPO levels and reticulocyte counts produced in response to anemia were sampled throughout the study and analyzed using a pharmacokinetic/pharmacodynamic (PK/PD) model.

RESULTS

The phlebotomy-induced drop in hemoglobin resulted in a increase in EPO levels, which reached a maximum of 764 +/- 55 mU/mL (mean +/- %CV) in 0.5-2.6 days. The reticulocyte counts increased from baseline values of 76.9 x 10(3) +/- 67/microL to 619 x 10(3) +/- 30/microL in 8 days. The PK/PD analysis indicated an increased maturation time for the reticulocytes (4.88 +/- 35 days) and demonstrated that the E(max) model for EPO's activation of the progenitors did not show significant effect saturation at the endogenous EPO levels reached.

CONCLUSIONS

In extrapolating from the animal pilot experiment, the present study provides a case for the use of higher r-HuEPO doses in human studies to determine if higher doses are more effective in treatment of neonatal anemia to reduce, and in some less severe cases, eliminate, the need for blood transfusions.

Is there a role for erythropoietin in neonatal medicine?

Since it was first cloned in 1985, the therapeutic potential of recombinant human erythropoietin in the neonatal hyporegenerative anaemias has been studied-the anaemia of prematurity and haemolytic disease of the newborn. Between 60% and 100% of preterm infants are transfused before three weeks of age, a large proportion receiving more than one transfusion. Blood transfusions are currently also the mainstay of treatment for the hyporegenerative anaemia encountered in neonates with Rhesus disease. Sometimes the situation is complicated by the religious beliefs of the parents. Blood transfusions are associated with numerous risks, from transmission of infection to local injury, and in an effort to minimize these risks Neonatologists have looked to recombinant erythropoietin. Despite an extensive number of studies, there is as yet no clear consensus as to whether the use of recombinant erythropoietin in Neonatal medicine minimizes the need for blood transfusions without risk to the neonate. In this article we review the evidence for and against the use of recombinant erythropoietin in Neonatal medicine.

Late erythropoietin for preventing red blood cell transfusion in preterm and/or low birth weight infants

BACKGROUND

Hematocrit falls after birth in preterm infants due to physiological factors and blood letting. Low plasma levels of erythropoietin (EPO) in preterm infants provide a rationale for the use of EPO to prevent or treat anemia.

PRIMARY OBJECTIVE

To assess the effectiveness and safety of late initiation of EPO (initiated at 8 days after birth or later) in reducing the use of red blood cell transfusions in preterm and/or low birth weight infants.

SECONDARY OBJECTIVES

Subgroup analyses of low (< 500 IU/kg/week) and high (> 500 IU/kg/week) doses of EPO and within these subgroups analyses of the use of low (< 5 mg/kg/day) and high (> 5 mg/kg/day) doses of supplemental iron, in reducing the use of red blood cell transfusions in these infants.

SEARCH STRATEGY

MEDLINE, EMBASE, CINAHL, abstracts from scientific meetings published in Pediatric Research and reference lists of identified trials and reviews were searched in November 2005/April 2006 and the Cochrane Central Register of Controlled Trials (CENTRAL, The Cochrane Library, Issue 2, 2006). No language restrictions were applied.

SELECTION CRITERIA

Randomised or quasi-randomized controlled trials of late initiation of EPO treatment (started at eight days of age or later) vs. placebo or no intervention in preterm (< 37 weeks) and/or low birth weight (< 2500 g) neonates. For inclusion the studies needed to provide information on at least one outcome of interest.

DATA COLLECTION AND ANALYSIS

Data were abstracted by the two authors on pre-tested data collection forms. Data were entered by one review author (AO) and checked for accuracy by the other (SA). Data were analysed using RevMan 4.2.8. The statistical methods included relative risk (RR), risk difference (RD), number needed to treat to benefit (NNTB), number needed to treat to harm (NNTH) for dichotomous outcomes and weighted mean difference (WMD) for continuous outcomes reported with their 95% confidence intervals (CI). A fixed effects model was used for meta-analyses. Heterogeneity tests including the I squared (I(2)) statistic were performed to assess the appropriateness of pooling the data.

MAIN RESULTS

Twenty-eight studies enrolling 1302 preterm infants in 21 countries were included. The quality of the trials varied. Most trials were of small sample size. Only one study clearly stated that infants were excluded if they had received red blood cell transfusion prior to study entry (Samanci 1996). A total of 19 studies including 912 infants reported on the primary outcome of "Use of one or more red cell transfusions". The meta-analysis showed a significant effect [typical RR; 0.66 (95% CI; 0.59, 0.74); typical RD -0.21 (95% CI; -0.26, -0.16); typical NNTB of 5 (95% CI 4, 6)]. There was statistically significant heterogeneity [for RR (p < 0.00001), I(2 )= 74.0% and for RD (p = 0.0006), I(2 )=58.9%]. Similar results were obtained in secondary analyses based on different combinations of high/low doses of EPO and iron supplementation. There was a significant reduction in the total volume (ml/kg) of blood transfused per infant (four studies enrolling 177 infants) [typical WMD = -7 ml (95% CI -12, -3)] and in the number of transfusions per infant (nine studies enrolling 567 infants); [typical WMD -0.78 (-0.97, -0.59)]. The effect size was less in a post hoc analyses of high quality studies compared to studies in which the quality was uncertain and in studies that used strict guidelines for red blood cell transfusions vs. studies that did not. There were no significant differences in mortality, retinopathy of prematurity, sepsis, intraventricular haemorrhage, periventricular leukomalacia, necrotizing enterocolitis, bronchopulmonary dysplasia, SIDS, neutropenia, hypertension, or length of hospital stay. Long-term neurodevelopmental outcomes were not reported.

AUTHORS' CONCLUSIONS

Late administration of EPO reduces the use of one or more red blood cell transfusions, the number of red blood cell transfusions per infant and the total volume of red blood cell transfused per infant. The clinical importance of the results for the latter two outcomes is marginal (< 1 transfusion per infant and 7 ml/kg of transfused red blood cells). Any donor exposure is likely not avoided as most studies included infants who had received red cell transfusions prior to trial entry. Late EPO does not significantly reduce or increase any of many important neonatal adverse outcomes including mortality and retinopathy of prematurity. Further research of the use of late EPO treatment to prevent donor exposure is not indicated. Research efforts should focus on limiting donor exposure during the first few days of life in sick neonates, when red blood cell requirements are most likely to be required and cannot be prevented by late EPO treatment.

Recombinant human erythropoietin therapy in low-birthweight preterm infants: a prospective controlled study

BACKGROUND

This study aimed to detect the effectiveness of recombinant human erythropoietin therapy in preventing premature anemia in low-birthweight preterm infants.

METHODS

A total of 292 premature infants who were born earlier than 33 gestational weeks and smaller than 1500 g birthweight were enrolled into the study. In addition to their conventional supportive therapy (medications), recombinant human erythropoietin 200 U/kg twice a week, subcutaneously, was given to randomly selected 142 premature infants for 6 weeks. The blood count variables and need for transfusions were compared with the remaining 150 premature infants during 6 months follow up.

RESULTS

Serum erythropoietin levels were 11.3 +/- 6.1 mU/mL and 38.3 +/- 19.1 mU/mL in the erythropoietin group before and at the fourth week of the study, respectively (P < 0.001). Reticulocyte counts of the group treated with erythropoietin were 146 x 10(6) +/- 28 x 10(6)/mL and 122 x 10(6) +/- 27 x 10(6)/mL at the fourth and seventh week of the study, respectively, and these values were significantly higher when compared with the control group (P < 0.001 and P < 0.001). At the same period, hematocrit values were also found to be higher in the treatment group than the control group (P < 0.001). Serum ferritin levels were lower in the treatment group compared with the control group at the fourth week of the study. No side-effects related to erythropoietin usage were encountered. The need for packed cell transfusions were 47% in the group treated with erythropoietin and 62.6% in the control group. A statistically significant difference was found for transfusion needs between the control and treatment groups (P < 0.001).

CONCLUSION

Recombinant erythropoietin is effective therapy for maintaining stable hematocrit levels in low-birthweight preterm infants and prevents the need for blood transfusions.

Human recombinant erythropoietin in the prevention and treatment of anemia of prematurity

Human recombinant erythropoietin has been studied extensively as treatment for a variety of anemias. Since in vitro studies showed the primary etiology of the anemia of prematurity to be insufficient serum erythropoietin concentrations, clinical trials have evaluated the administration of human recombinant erythropoietin to preterm infants to treat this indication. These studies were followed by pharmacokinetic determinations in animal models and preterm infants, which revealed that preterm infants required greater doses of human recombinant erythropoietin because of a more rapid clearance and greater volume of distribution. Recent studies have focused on the administration of human recombinant erythropoietin in the first weeks of life to alleviate the anemia caused by excessive phlebotomy losses, and to prevent the anemia of prematurity. In addition, human recombinant erythropoietin has been tried clinically in a variety of neonatal populations in an attempt to decrease or eliminate transfusions. Although much information has been accumulated about the clinical use of human recombinant erythropoietin in preterm infants over the last 15 years, many questions remain unanswered. The evolution of clinical practice in the care of extremely low birthweight infants continues to affect the number of transfusions. It is likely that human recombinant erythropoietin administration in combination with instituting rigorous transfusion guidelines and decreasing phlebotomy losses will have the greatest impact in decreasing transfusion requirements in all preterm and term neonates, regardless of the etiology of their anemia.

Effects of early erythropoietin therapy on the transfusion requirements of preterm infants below 1250 grams birth weight: a multicenter, randomized, controlled trial

OBJECTIVES

Infants of </=1250 g birth weight receive multiple erythrocyte transfusions during their hospitalization. We hypothesized that early erythropoietin (Epo) and iron therapy would 1) decrease the number of transfusions received (infants 401-1000 g birth weight; trial 1) and 2) decrease the percentage of infants who received any transfusions (1001-1250 g birth weight; trial 2).

METHODS

A total of 172 infants in trial 1 and 118 infants in trial 2 were randomized to treatment (Epo, 400 U/kg 3 times weekly) or placebo/control. Therapy was initiated by 4 days after birth and continued through the 35th postmenstrual week. All infants received supplemental parenteral and enteral iron. Complete blood and reticulocyte counts were measured weekly, and ferritin concentrations were measured monthly. Transfusions were administered according to protocol. Phlebotomy losses and transfusion data were recorded.

RESULTS

Treated and placebo/control infants in trial 1 received a similar number of transfusions (4.3 +/- 3.6 vs 5.2 +/- 4.2, respectively). A similar percentage of treated and control infants in trial 2 received at least 1 transfusion (37% vs 46%). Reticulocyte counts were higher in treated infants during each week of the study in both trials. Hematocrits were higher among treated infants from week 2 on in both trials. Ferritin concentrations were higher in placebo/controls than in treated infants at weeks 4 and 8 in trial 1 and at week 4 in trial 2. No adverse effects of Epo or supplemental iron occurred.

CONCLUSION

The combination of early Epo and iron as administered in this study stimulated erythropoiesis in infants who were </=1250 g at birth. However, the lack of impact on transfusion requirements fails to support routine use of early Epo.neonate, intravenous iron, donor exposure.

Red blood cell transfusions in very and extremely low birthweight infants under restrictive transfusion guidelines: is exogenous erythropoietin necessary?

OBJECTIVE

To examine the number and volume of red blood cell transfusions (RBCTs) in very and extremely low birthweight infants under restrictive red blood cell transfusion guidelines without erythropoietin administration, and to compare the results with those reported in similar infants receiving erythropoietin.

METHODS

From April 1996 to June 1999, all RBCTs given to infants with a birth weight of less than 1500 g were prospectively recorded. Data on RBCT combined with erythropoietin treatment and RBCT guidelines were extracted from four prospective randomised trials of erythropoietin for anaemia of prematurity.

RESULTS

When the restrictive RBCT guidelines were followed, the number of RBCTs and volume transfused were similar to those reported during erythropoietin administration.

CONCLUSIONS

RBCT guidelines may have a similar impact on RBCT in very low birthweight infants to the administration of erythropoietin. The effect of RBCT guidelines on RBCT frequency should be considered when evaluating the efficacy of erythropoietin administration to preterm infants.

Haemolytic disease of newborn

Hemolytic disease of the newborn (HDN) occurs due to maternal IgG antibodies crossing the placenta thereby producing hemolysis mainly due to Rh, ABO and Kell groups. A systematic approach to the Rh HDN involves an obstetric history of previous isoimmunized baby, timing and regular monitoring of maternal Rh antibodies and pigment assay of amniotic fluid. Timely decision regarding in utero transfusion and early termination of pregnancy based on the maternal monitoring has radically improved the outcome of these babies. Antenatal prophylaxis with anti D has resulted in great reduction in the magnitude of Rh problem. The fetal blood sampling and in-utero intravenous transfusions has made it possible for almost 100% survival of isoimmunized pregnancies without hydrops. Alternative methods--IVIG and plasma exchange are still of limited application. ABO HDN though common is not a serious form of disease and dose not warrants invasive antenatal monitoring. Anti-Kell is found in patients having received multiple transfusions and the rapid progress of hemolysis in them may not allow such systematic follow up as in Rh HDN.

The use of erythropoietin in neonates

Although much information has been accumulated about the clinical use of Epo in preterm infants, many questions remain unanswered. The evolution of clinical practice in the care of extremely ill, preterm infants continues to affect the number of transfusions required during hospitalization. Decreasing phlebotomy losses and instituting standardized transfusion guidelines have both been shown significantly to decrease the transfusion requirements of preterm infants. The administration of Epo likely decreases transfusion need even further; however, the direct impact of each of these actions has not been studied prospectively. It is likely that the combination of instituting rigorous and standardized transfusion guidelines, decreasing phlebotomy losses, and the appropriate use of Epo will have the greatest impact in decreasing transfusion requirements in all preterm and term neonates, regardless of the cause of their anemia.

Effect of early versus late administration of human recombinant erythropoietin on transfusion requirements in premature infants: results of a randomized, placebo-controlled, multicenter trial

OBJECTIVE

The administration of recombinant human erythropoietin (rHuEPO), started after the first 2 weeks of life, reduces the transfusion requirement in premature infants. However, its use throughout the first 2 weeks of life, when anemia results predominantly from phlebotomy losses, remains controversial. We investigated whether early use of rHuEPO would reduce the total transfusion requirement and/or the number of transfusions throughout the first 2 weeks of life.

METHODS

We randomized 114 infants with birth weight (BW) <1250 g to receive rHuEPO (1250 units/kg/week; IV; early group: n = 57) or placebo (late group: n = 57) from day 2 to day 14 of life; subsequently, all the patients received rHuEPO (750 units/kg/week, subcutaneously) for 6 additional weeks. All infants were given oral iron (6 mg/kg/day) and folic acid (2 mg/day).

RESULTS

The early group showed higher hematocrit and reticulocyte counts than the late group in the first 3 weeks of life, but there was no difference in the total number of transfusions (early: 1.8 +/- 2.3 vs late: 1.8 +/- 2.5 transfusion/patient) or the transfusion requirement throughout the first 2 weeks of life (early:.8 +/- 1.1 vs late:.9 +/- 1.3) could be demonstrated. In infants with BW <800 g and total phlebotomy losses >30 mL/kg (n = 29), a lower number of transfusions was received by infants in the early group, compared with late group, from the second week to the end of the treatment (early: 3.4 +/- 1.1 vs late: 5.4 +/- 3.7 transfusion/patient). No clinical adverse effects were observed. Thrombocytosis was detected during the treatment with rHuEPO in 31% of the infants.

CONCLUSIONS

In the whole population, the early administration of rHuEPO induced a rise of reticulocyte counts, but not enough to reduce the transfusion requirement. The most severely ill infants (BW <800 g and phlebotomy losses >30 mL/kg) seemed to benefit from early use of rHuEPO, and this deserves additional study.

Blood banking issues pertaining to neonatal red blood cell transfusions

Many preterm infants are given multiple red blood cell transfusions during the early weeks of life. Because firm standards for neonatal transfusions do not exist, it is important to consider the pathophysiology of the anemia of prematurity, the goals of transfusion therapy and blood banking practices that best provide safe and effective neonatal transfusions. There is increasing agreement that efforts continue to minimize phlebotomy blood losses, to transfuse per conservative indications and to limit donor exposure by transfusing stored red blood cells from a single unit reserved for an infant--rather than insisting on fresh blood.

The effect of recombinant human erythropoietin on circulating hematopoietic progenitor cells in anemic premature infants

In vitro and animal studies suggest that high concentrations of recombinant human erythropoietin (rHuEPO) might divert multipotent progenitors into erythroid maturation at the expense of granulocyte production. We determined whether changes of number and lineage commitment of peripheral blood progenitor cells occur in premature infants during therapy with rHuEPO. Thirty preterm infants were randomly assigned either to receive 300 IU of eopoetin alpha s.c. per kilogram body weight three times a week for four weeks or to a control group. At study entry and after two weeks of treatment the numbers of circulating BFU-E, granulocyte-macrophage colony-forming units (CFU-GM) and granulocyte-erythrocyte-macrophage-megakaryocyte CFU (CFU-GEMM) were analyzed by semisolid culture technique, CD34+ cells and early myeloid CD34+CD45RA- progenitors by flow cytometry. As compared with the control group, rHuEPO treatment did not exert any significant modulatory effect on numbers of CFU-GM, nor was there a significant change in numbers of BFU-E, CFU-GEMM, total-CFU, percentage of CD34+ or CD34+CD45RA- cells. Mean neutrophil count was not significantly reduced at any period during the study. Compared with the control group, the infants receiving rHuEPO had higher hematocrit values (p = 0.003) and absolute reticulocyte counts (p < 0.001). The median cumulative volume of blood transfused per kilogram per day was 0.86 ml (first quartile 0.5 ml; third quartile 1.1 ml) in the control group and 0 ml (first quartile 0 ml; third quartile 0.47 ml) in the rHuEPO group (p = 0.038). We conclude using a relatively high dose of rHuEPO in premature infants, no significant in vivo effect on circulating peripheral blood progenitor or neutrophil count could be detected.

Use of Hematopoietic Growth Factors in the Neonatal Intensive Care Unit

Recombinant hematopoietic growth factors have emerged as valuable treatments for a variety of medical conditions. Recently, their applications have reached the neonatal intensive care unit, where they offer new therapeutic options for problems as common as anemia of prematurity, or as catastrophic as neonatal sepsis. When facing bacterial infection, it is known that newborn infants are capable of increasing their serum G-CSF concentrations. However, their response does not reach the concentrations that adults are able to achieve, and frequently neutropenia complicates the picture of neonatal sepsis. Although Phase III clinical trials are still in progress, published animal studies, case reports, and Phase I trials suggest that neonates with a variety of neutropenias experience a rapid elevation in their blood neutrophil concentration following administration of rG-CSF, without significant adverse effects. Although many factors contribute to the development of the “anemia of prematurity,” one of the major factors is the inability of preterm infants to generate an erythropoietin (Epo) response appropriate to their degree of anemia. On the basis of this fact, administration of rEpo to preterm neonates to treat or to prevent the anemia of prematurity has been the subject of multiple clinical studies, and it is now clear that rEpo administration to this population can indeed result in lower transfusion requirements, with only occasional and mild adverse effects. Neonatal thrombocytopenia is also a frequent clinical problem, which in most patients develops without a clear underlying cause. Recent studies, quantifying circulating megakaryocyte progenitors in the peripheral blood of thrombocytopenic neonates, suggest that impaired megakaryocytopoiesis may be the main underlying mechanism of many cases of thrombocytopenia. On the basis of this finding, it is tempting to speculate that recombinant thrombopoietin, the newly discovered physiological stimulator of platelet production, will be of clinical relevance in the treatment of thrombocytopenic neonates.

The role of erythropoietin in the anemia of prematurity

Neonatal erythropoiesis is limited by a relatively inadequate production of erythropoietin. This is likely the result of dependence on the hepatic production of erythropoietin and an incomplete switchover to renal production. The present model of neonatal erythropoiesis suggests that the use of exogenous erythropoietin should correct the early anemia of prematurity that is observed at 6 weeks of age in premature newborns. Randomized, controlled trials of erythropoietin use in very low birthweight infants are reviewed. The data support the conclusion that erythropoietin at doses of > or = 750 u/kg/wk started at less than 7 days of age results in improved reticulocyte counts and hemoglobin levels, but does not reduce the number of infants who will be exposed to blood products. Erythropoietin at doses of > or = 600 u/kg/wk started at an average of 21 days of life improves reticulocyte counts and hemoglobin levels, and reduces the number of infants will will require late transfusion, but does nothing for the bulk of infants who are transfused before that age.

Management of late anemia in Rhesus hemolytic disease: use of recombinant human erythropoietin (a pilot study)

The management of (Rhesus) hemolytic disease of the fetus and newborn includes intrauterine transfusions to prevent the development of hydrops, treatment of the possible hyperbilirubinemia in the immediate postnatal period, and treatment of late anemia. Low levels of serum erythropoietin due to suppression of the bone marrow by multiple intrauterine transfusions is a suggested mechanism for this anemia. The aim of our study was to test whether recombinant human erythropoietin reduced the need for erythrocyte transfusions in these infants. Twenty infants with Rhesus isoimmunization were blindly randomized to treatment and control groups at the 2nd wk of life. The number of intrauterine and exchange transfusions and demographic data were similar in both groups. The infants in the treatment group received recombinant human erythropoietin, s.c. 200 U/kg of body weight three times a week for a period of 6 wk, whereas the infants in the control group received a placebo for the same period. In the treatment group, the mean number of erythrocyte transfusions was significantly lower than that of the control group (1.8 versus 4.2). The reticulocyte counts and Hb levels rose earlier in the treatment group. The platelet and neutrophil counts were similar in both groups throughout the study. This study demonstrates that recombinant human erythropoietin treatment decreases the need for erythrocyte transfusions in the late anemia of infants with Rh isoimmunization. Considering the risks of blood transfusions, this decrease in the donor exposure is worthwhile.

Comparison of high dose therapy of rhEPO, given two or three times a week in premature infants

We investigated the question whether there is a difference in the response to high dose human recombinant erythropoietin (rhEPO) given twice or three times weekly in premature infants. 48 premature infants were randomly assigned to receive 300 U/kg rhEPO three times a week or 450 U/kg two times a week for at least 4 weeks and up to 6 weeks. Concomitant oral iron supplementation was compulsory, median daily dosage reached 6.6 mg/kg, doses exceeding 8 mg/kg/d were not tolerated. Our data showed no differences in the two groups in regard to hematocrit (HCT), reticulocytes and ferritin levels. A marked increase in reticulocyte counts could be observed in both groups. Serum ferritin decreased as expected. Premature infants starting with a baseline HCT lower than 32% showed a steady increase in HCT without any initial decline. No adverse effects could be observed in either group. Since there is no difference in the response to high dose rhEPO given two or three times weekly, we therefore conclude that the twice weekly regimen is compatible with outpatient treatment.

Reducing donor exposure in preterm infants requiring multiple blood transfusions

Preterm infants frequently require multiple blood transfusions. Traditionally, 'fresh' (less than seven days old) blood has been used but this often results in transfusions from multiple donors. To reduce donor exposure the policy for top-up transfusions was changed. A unit of blood under five days old with additional satellite packs was ordered for each infant and used up to its expiry date, allowing up to eight transfusions from a single donation to be given. The mean (SD) number of transfusions per infant in 43 infants transfused according to previous policy and in 29 transfused according to the new policy was similar at 5.6 (4.0) and 5.3 (3.1), respectively. However, donor exposure fell following the change in policy from 4.9 (3.5) to only 2.0 (0.9). Only one infant was exposed to more than three donors compared with 24 infants in the control group. Plasma potassium concentrations were not significantly different following transfusion of blood stored for up to 33 days. This simple change in policy has reduced donor exposure in infants requiring multiple top-up transfusions.

Neonatal anemia: pathophysiology and treatment

All neonates experience a decline in circulating red blood cell (RBC) mass due to diminished erythropoietin (EPO) levels. This effect is more pronounced in small, premature infants and can lead to severe anemia and need for RBC transfusions--particularly, if repeated phlebotomy is required to monitor acutely-ill neonates. Although optimal RBC transfusion therapy has been a long-term challenge for neonatologists, the emergence of recombinant EPO as promising therapy for neonatal anemia is the major issue for 1994. Accordingly, this report for the 12th International Convocation on Immunology (Transfusion Immunology and Medicine) will focus on this aspect of neonatal transfusion medicine. Although several controlled trials to evaluate EPO as therapy have been completed, definitive answers to all questions regarding efficacy and possible toxicity have not been provided. However, therapy with EPO plus iron and adequate nutrition is likely to be proven effective for the relatively late anemia of stable prematures. To date, EPO has not been shown, convincingly, to alleviate the anemia present early in the life of acutely-ill, premature infants.

The effect of epoetin beta (recombinant human erythropoietin) on the need for transfusion in very-low-birth-weight infants. European Multicentre Erythropoietin Study Group

BACKGROUND

Anemia of prematurity is characterized by low reticulocyte counts and inadequate erythropoietin response, for which many very-low-birth-weight infants receive multiple blood transfusions. We investigated whether early treatment of such infants with recombinant human erythropoietin would reduce their need for transfusions.

METHODS

We performed a controlled, blinded trial in 241 infants with very low birth weights at 12 centers in six European countries. When three days old, the infants were randomly assigned either to the epoetin group or to the control group. Those in the epoetin group received 250 IU of epoetin beta per kilogram of body weight subcutaneously three times a week from day 3 to day 42 (for a total of 17 doses); those in the control group did not receive this drug. Infants in both groups received oral iron (2 mg per day) from day 14 onward.

RESULTS

The control infants needed a mean of 1.25 transfusions each, as compared with 0.87 transfusion for epoetin-treated infants (P = 0.013). The median cumulative volume of blood transfused per kilogram per day was 0.41 ml in the control group (first quartile, 0 ml; third quartile, 0.8 ml) and 0.09 ml in the epoetin group (first quartile, 0 ml; third quartile, 0.8 ml) (P = 0.044). The rate of success, defined as an absence of need for transfusions and a hematocrit that never fell below 32 percent, was 4.1 percent in the control group and 27.5 percent in the epoetin group (P = 0.008). Epoetin was most beneficial in boys with birth weights of 1200 g or more and a base-line hematocrit of 48 percent or more. No toxic effects were observed in the epoetin group; as compared with the control group, the epoetin group had an increased incidence of septicemia (14 vs. 7 episodes, P not significant) and reduced weight gain (520 vs. 571 g, P = 0.02).

CONCLUSIONS

Infants with very low birth weights have less need of transfusions if given epoetin beta during the first six weeks of life (250 IU per kilogram three times a week). We recommend early epoetin treatment for all such infants, but further studies of nutrition and iron supplementation during treatment are needed.

The in vitro effects of stem cell factor, interleukin 3 and granulocyte-macrophage colony stimulating factor on haemopoietic progenitor cells from premature infants

Circulating haemopoietic progenitor cells from premature infants were assessed for their ability to respond to interleukin 3, granulocyte-macrophage colony stimulating factor and stem cell factor (SCF) in vitro. All three cytokines increased the number of colonies derived from burst forming units erythroid (BFU-E), colony forming units granulocyte-macrophage (CFU-GM) and multi-lineage progenitors (CFU-Mix) grown in the presence of erythropoietin (Epo). The size and haemoglobin content of BFU-E derived colonies also increased in the presence of the cytokines. Of those tested, SCF was found to be the most potent additive to Epo for the enhanced growth of BFU-E and CFU-Mix. In short-term liquid cultures without Epo, SCF alone induced globin synthesizing cells. Progenitors from premature infants were at least as responsive to all three cytokines as those from healthy adults. The use of SCF in combination with Epo in the prevention or treatment of anaemia in premature infants warrants further investigation.

Suppression of erythropoiesis by intrauterine transfusions in hemolytic disease of the newborn: use of erythropoietin to treat the late anemia

Hemolytic disease of the fetus and newborn has three phases of anemia: in utero, in the first week of life, and in the weeks and months after birth. Intrauterine transfusions can ameliorate the severity of both fetal and early anemia, but late anemia and the need for transfusion remain significant problems. Bone marrow hypoplasia--probably a result of suppression of erythropoiesis from the intrauterine transfusions--was documented in the three patients tested in our study. Because erythropoietin (EPO) levels have been found to be low (i.e., normal) in these previously transfused patients despite the degree of anemia, we treated four affected infants with EPO, 200 microliters/kg subcutaneously three times a week, and noted reticulocytosis and increased hemoglobin values 2 to 4 weeks later. One patient again had reticulocytopenic anemia when the EPO therapy was stopped but responded to retreatment. Our study indicates that EPO treatment may be effective in the management of late anemia and could help to decrease the need for postnatal transfusions.

A system approach to pharmacodynamics. Plasma iron mobilization by endogenous erythropoietin in the sheep fetus; evidence of threshold response in spontaneous hypoxemia

At present, nearly all infants with birth weights of < 1 kg receive blood transfusions for treatment of clinical signs of tissue hypoxia resulting from anemia of prematurity. In contrast to the successful use of recombinant human erythropoietin (rhEp) in adults, treatment of anemic neonates with rhEp to stimulate red cell production and reduce the need for transfusions that pose serious infectious and immunologic risk has not been effective. The present study investigates the pharmacodynamics (PD) of endogenous erythropoietin (Ep) in sheep fetuses to determine possible causes for the poor rhEp response in early development. The dynamic relationship between plasma Ep and plasma iron resulting from spontaneous hypoxemic episodes is investigated by PD system analysis. The erythropoietic effect of Ep is measured in terms of the mobilization of plasma iron needed in the production on new erythrocytes. A hysteresis minimization approach is employed to determine the intrinsic PD dose-response relationship (transduction) of Ep. The dose-response relationship shows a well-defined threshold level that has to be exceeded before Ep begins to show a significant effect on plasma iron. It is postulated that the threshold mechanism may serve a useful purpose during early development by reducing the risk of the fetus developing a pathological degree of polycythemia and hyperviscosity in the relatively hypoxemic fetal environment. At the same time, the threshold serves the purpose of providing a needed response to more severe pathologic hypoxemic episodes. The occurrence of anemia during subsequent postnatal life when PaO2 levels increase markedly may be the inevitable, but unfortunate corollary of a continuation of this mechanism.(ABSTRACT TRUNCATED AT 250 WORDS)

Interleukin-3, interleukin-6, granulocyte-macrophage colony-stimulating factor and erythropoietin cord blood levels of preterm and term neonates

The cascade of known haematopoietic growth factors controlling granulomonopoiesis and erythropoiesis includes interleukin-3 (IL-3), interleukin-6 (IL-6), granulocyte-macrophage colony-stimulating factor (GM-CSF), and erythropoietin (EPO). Elevated endogenous IL-3 and IL-6 cord blood levels in infection-free premature and mature neonates may reflect their possible role for expansion of haematopoietic progenitor cells, granulocytes and monocytes. Within the erythroid lineage a synergistic action of IL-3, IL-6 and EPO can be assumed. To identify the regulatory role in fetal haematopoietic expansion cord blood plasma levels of these haematopoietic growth factors were assessed in 19 premature and 20 mature infants using commercial enzyme-linked immunosorbent assay and enzyme-amplified sensitivity immuno assay test kits. Peripheral blood IL-3, GM-CSF and EPO were studied in 5 and 10 premature infants respectively. Compared with cord blood levels we found a decline in EPO levels but no decrease of IL-3 and GM-CSF during the 1st month of life. We conclude that postnatal decrease in plasma burst-promoting activity levels in preterm infants is mainly explained by low postnatal EPO levels.

Erythropoietin, protein, and iron supplementation and the prevention of anaemia of prematurity

The effectiveness of recombinant human erythropoietin (r-HuEpo) in raising haemoglobin concentrations in very low birthweight infants was examined in a randomised multicentre study. Twenty nine 'healthy' appropriate for gestational age infants with birth weights 900-1400 g entered the study at 3 weeks of age. All infants received breast milk supplemented with 9 g/l human breast milk protein from 3 to 8 weeks of age. Eighteen mg iron was given daily from week 3 and was doubled if serum iron concentration fell below 16.0 mumol/l. Fourteen infants were randomised to receive 100 U/kg r-HuEpo subcutaneously three times a week from week 3 to week 7; 15 infants served as controls. After one week reticulocyte and haemoglobin concentrations were significantly higher in the r-HuEpo treated group and the haemoglobin values remained significantly higher throughout r-HuEpo treatment and at the concentrations observed in full term infants. No adverse effects were associated with the treatment. In stable very low birthweight infants with optimal iron and protein intakes, moderate dose r-HuEpo can produce significant gains in red cell production that may be clinically useful.

Double blind trial of recombinant human erythropoietin in preterm infants

Twenty four infants between 27 and 33 weeks' gestation were recruited into a double blind study to investigate the use of recombinant human erythropoietin (r-HuEpo) for the prevention of anaemia of prematurity. Between 50 and 150 U of r-HuEpo (n = 16) or placebo was administered subcutaneously twice a week from 7 days of age until discharge. There was a significant increase in the reticulocyte count in infants receiving r-HuEpo sustained from the second week of treatment until discharge compared with placebo. There was a reduction in the number of transfusions required in the r-HuEpo group with only 47% requiring a transfusion compared with 87% in the placebo group. During treatment with r-HuEpo there was a significant rise in the red cell folate concentration, a significant fall in the ferritin concentration, and a significantly higher percentage of haemoglobin F at discharge suggesting active erythropoiesis. The study provides strong evidence for the efficacy of r-HuEpo in stimulating erythropoiesis and reducing the requirement for transfusions for anaemia of prematurity.

Recombinant human erythropoietin in the treatment of infants with anaemia of prematurity

Recombinant human erythropoietin (rHuEPO) was administered subcutaneously three times a week to 18 infants with the anaemia of prematurity at doses of 75, 150, 300, or 600 units/kg per week for 4 weeks, starting at 3-4 weeks of postnatal age. A significant and dose-dependent increase in reticulocyte count was observed from a mean baseline value of 71 x 10(9)/l to 200 x 10(9)/l after 3 weeks of therapy, compared with a change from 69 to 97 x 10(9)/l in 66 historical controls. The haematocrit value remained unchanged during rHuEPO treatment, whereas it steadily declined until 9 weeks of postnatal age in the controls. These effects were accompanied by a marked reduction in serum iron concentration and transferrin saturation in patients receiving standard-dose iron supplements, but not in those given larger doses. Only 3 of 18 patients required a red blood cell transfusion. These infants were among the most anaemic at entry into the study and 2 of them were unable to complete rHuEPO therapy, while the third developed iron deficiency anaemia. These data indicate that rHuEPO with appropriate iron supplementation may accelerate the recovery from anaemia of prematurity. Larger scale placebo-controlled studies are now needed to confirm these findings and verify their impact on transfusion requirements of premature infants.

Effect of high doses of human recombinant erythropoietin on the need for blood transfusions in preterm infants

To determine whether prophylactic treatment with recombinant human erythropoietin (rHuEPO) and iron would reduce the need for blood transfusions, we randomly assigned 22 premature infants with gestational ages less than or equal to 32 weeks and birth weights less than or equal to 1.75 kg to receive rHuEPO, 400 IU/kg three times a week, plus iron, 20 mg/wk intravenously, from the second day of life (11 infants), or no rHuEPO and no iron (11 infants). The two groups had similar birth weights and clinical variables. The treated infants required fewer blood transfusions (0.8 +/- 1.5 vs 3.1 +/- 2.1; p = 0.01) and less volume of packed erythrocytes (14.2 +/- 25.9 vs 48.4 +/- 34.0 ml/kg; p = 0.02). The amounts of blood sampled were not different (19.5 +/- 21.1 vs 27.8 +/- 19.1 ml/kg; p = 0.35). Reticulocyte and hematocrit values were higher in the treated group (4.46% +/- 0.8% vs 1.49% +/- 1.1% (p = 0.0001) and 48.1% +/- 7.3% vs 43.8% +/- 4.7% (p = 0.004), respectively). No side effects of either rHuEPO or intravenously administered iron were noted. These data indicate that rHuEPO, in combination with iron supplementation, is effective in reducing the need for blood transfusions in the premature infant. More information is needed on dosage, timing, and iron and vitamin supplementation.

Enhancement of erythropoiesis by recombinant human erythropoietin in low birth weight infants: a pilot study

We randomly assigned eight concurrently symptom-free premature infants (birth weight less than or equal to 1250 gm) at high risk of requiring erythrocyte transfusions for anemia of prematurity to 6 weeks of intensive treatment with either subcutaneous recombinant human erythropoietin (r-HuEPO group) or a placebo (control group). Treatment with r-HuEPO was initiated at a dose of 100 units/kg per day 5 days a week, and was increased to 200 units/kg per day after 2 or 3 weeks if target reticulocyte counts were not achieved. All patients were given supplemental oral iron therapy at a dose of 6 mg/kg per day, as tolerated. Mean reticulocyte counts in r-HuEPO-treated and control infants were 64,600 versus 67,500 cells/mm3 at entry; were 245,600 versus 78,000 cells/mm3 after 1 week; and averaged 262,600 versus 136,400 cells/mm3 during the study. Mean reticulocyte counts in r-HuEPO-treated infants were 251,200 cells/mm3 during the week when r-HuEPO, 100 units/kg per day, was given, and were 269,500 cells/mm3 after the dose was increased to 200 units/kg per day. Mean hematocrit values at entry were 33.4% in babies who received r-HuEPO versus 33.6% in the control subjects, and were 31.4% in r-HuEPO-treated and 25.2% in the control subjects at the end of treatment. One r-HuEPO-treated and three control babies received transfusions during the study; the total volume of blood given was 17 ml in the r-HuEPO group and 101 ml in the control subjects. The percentage of hemoglobin F increased in infants not given transfusions. We conclude that r-HuEPO stimulates endogenous erythropoiesis in small premature babies who are receiving supplemental oral iron therapy. A controlled multicenter trial has been undertaken to confirm these promising preliminary observations.

Case study. Erythropoietin for anaemia in a preterm Jehovah's Witness baby

An infant born at 24 weeks gestation to Jehovah's Witness parents was made a Ward of Court and treated against their wishes with blood products. Erythropoietin was used without obvious benefit, but the child did well. The parents did not reject the child and maintained a good relationship with medical and nursing staff. We present this case in the light of current discussions on child welfare and recent reform of the law relating to child protection and highlight the many difficult dilemmas faced by the medical team.

Recombinant erythropoietin compared with erythrocyte transfusion in the treatment of anemia of prematurity

To assess the risks and benefits of erythropoietin versus erythrocyte transfusion in the treatment of the anemia of prematurity, we randomly assigned 19 anemic preterm infants (birth weight 988 +/- 227 gm; gestational age 27.6 +/- 1.2 weeks; age 41 +/- 15 days; all values mean +/- SD) to receive either transfusion or subcutaneously administered erythropoietin (200 units/kg every other day for 10 doses). In the 10 erythropoietin recipients, corrected reticulocyte counts increased from 2% +/- 1% to 7% +/- 2% (p less than 0.001) and hematocrits increased from 27% +/- 2% to 30% +/- 4% (p less than 0.05). In the nine infants who underwent transfusion, reticulocyte counts did not increase, but hematocrits increased from 28% +/- 4% to 41% +/- 2% after initial transfusion (p less than 0.001) and had decreased to 34% +/- 5% by day 20. Signs attributed to anemia (tachycardia, apnea with bradycardia, and poor weight gain) declined in both the erythropoietin recipients and those who underwent transfusion. However, five of nine infants who underwent transfusion had symptoms within 10 to 14 days and were given further transfusions. Marrow aspiration performed after 7 to 10 days of treatment showed that infants receiving erythropoietin had greater percentages of erythropoietic precursors (p less than 0.01), greater concentrations of mature erythroid progenitors (p less than 0.001), and higher cycling rates of erythroid progenitors (p less than 0.001). The percentage of mature stored neutrophils in marrow was lower in the erythropoietin group than in the transfusion group, resulting in an inverse myeloid/erythroid ratio (0.5:1 vs 6.2:1; p less than 0.001). After 20 days, absolute blood neutrophil counts were lower in the erythropoietin recipients (1.8 +/- 0.9 x 10(3) cells/microliters) than in the infants who underwent transfusion (3.9 +/- 1.9 x 10(3) cells/microliters; p less than 0.05). Administration of erythropoietin thus stimulated erythropoiesis and relieved signs attributed to anemia; the significance of the relative neutropenia remains to be determined. We conclude that erythropoietin administration offers promise as an alternative to erythrocyte transfusion in neonates with symptomatic anemia of prematurity.

Weekly intravenous administration of recombinant human erythropoietin in infants with the anaemia of prematurity

To study the safety and efficacy of administering human recombinant erythropoietin (rHuEPO) to infants with anaemia of prematurity, a combined phase I/II trial of weekly intravenous injections for 4 weeks was undertaken. We treated 16 infants with 10, 25, 50, 100 or 200 units/kg body weight in groups of two to four patients per dose level. They were all born prematurely (mean gestational age: 29 weeks; range 27-32), had a mean post-natal age of 42 days (range: 25-59) and haemoglobin concentration of 87 g/l (range: 72-94) when treatment was started. Four patients (25%) needed a transfusion during the trial, one at day 7 treated with 10 units/kg and 3 at days 15, 25, 29 with 100 units/kg. In the others, a progressive rise in mean haemoglobin values was seen in each group after 21 days of treatment, without a dose-dependent effect. A positive change in absolute reticulocyte counts with a peak after 7-14 days of therapy was observed with low (25-50 units/kg) but not with higher doses, with a significant difference at day 14 between 25 and 100 units/kg (P less than 0.01). A dose-limiting severe neutropenia (absolute neutrophil count less than 0.5 x 10(9)/l) occurred transiently in five patients, with doses greater than 25 units/kg. No infectious complication and no sign of iron deficiency were observed. Weekly low doses of rHuEPO appear safe, convenient to administer and able to induce a reticulocytic response in infants with anaemia of prematurity. A phase III placebo-controlled trial is needed to confirm these results. Neutropenia associated with rHuEPO administration in infants might be related to their stage of human ontogeny.

Erythropoietic progenitor cells from premature neonates studied using a validated serum-deprived medium

We have examined a serum-deprived culture system in order to verify that it is suitable for the study of burst forming unit erythroid (BFU-E) progenitor cells from premature neonates. Optimum growth of BFU-E from premature neonates was observed with each media constituent using the same concentration as that previously described for adult subjects. Growth of immature BFU-E from premature neonates were highly dependent upon a source of Burst Promoting Activity and mature BFU-E derived colonies emerged at day 12 compared to day 14 in adults. Our preliminary results with the validated medium suggest that premature infants have increased peripheral blood concentrations of BFU-E compared to healthy adult controls.

Recombinant human erythropoietin in the anemia of prematurity: results of a placebo-controlled pilot study

Experimental and clinical data implicate inadequate erythropoietin production as an important reason that infants acquire this anemia and suggest that recombinant human erythropoietin (r-HuEPO) might be used to treat or prevent it. We therefore randomly assigned 20 small premature infants (birth weight less than or equal to 1250 gm) who were highly likely to require erythrocyte transfusions for anemia of prematurity to receive 6 weeks of treatment with either intravenously administered r-HuEPO (at a dose of 100 units/kg twice each week) or a placebo. Hematologic measurements, transfusion requirements, and growth were followed during therapy and for 6 months thereafter. Treated (EPO) and control babies did not differ with respect to weight, hematocrit, overall mean absolute reticulocyte count, calculated erythrocyte mass, or rate of growth. However, reticulocyte counts increased earlier in patients given r-HuEPO. Six of ten babies in the EPO group, and 8 of 10 assigned to the control group, received at least one erythrocyte transfusion during treatment. For all infants the amount of blood sampled for laboratory tests was strongly predictive of the volume of packed erythrocytes transfused (r = 0.890; p = 0.0001). Of nine infants who had less than 20 ml packed erythrocytes removed for laboratory tests, none of four given r-HuEPO received a transfusion, whereas three of five infants assigned to the placebo group received one. No toxic effects were attributable to r-HuEPO, and no significant changes in leukocyte or platelet counts occurred during treatment. Reticulocyte counts were correlated with simultaneous platelet counts and were inversely related to absolute neutrophil counts in both study groups. We conclude that r-HuEPO administration is safe and feasible at the dose studied. Additional controlled trials utilizing higher doses of r-HuEPO and larger numbers of patients are justified.

Effects of intravascular, intrauterine transfusion on prenatal and postnatal hemolysis and erythropoiesis in severe fetal isoimmunization

In an investigation of the effects of intrauterine, intravascular transfusions (IUT) on fetal and neonatal hemolysis and erythropoiesis, 12 fetuses who received IUT for treatment of severe isoimmunization had serial measurements of hemoglobin concentration, Kleihauer-Betke stains to detect fetal hemoglobin-containing erythrocytes, and determination of plasma erythropoietin (EPO) concentration before each IUT, at birth, and postnatally. Reticulocyte counts and sensitizing antibody titers were measured in five fetuses. Mean values before the first IUT, before the final IUT, and at birth were as follows: hemoglobin level, 6.1, 9.1, and 11.3 gm/dl; reticulocyte count, 22.7%, 0.5%, and 0.9%; fetal hemoglobin-containing erythrocytes, 100%, 1.6%, and 1.5%; and EPO level, 12, 56, and 756 mU/ml, respectively. Only one neonate required exchange transfusion. In the first month postnatally, all infants had a profound anemia. All but one infant required simple blood transfusions postnatally. Before the first postnatal transfusion, mean hemoglobin concentration was 6.2 gm/dl, mean reticulocyte count was 0.8%, mean erythropoietin concentration was 23 mU/ml, and the sensitizing antibody titer remained markedly elevated. Except for the surge of EPO at birth, EPO levels did not rise prenatally or postnatally unless marked anemia (hemoglobin level less than 5 gm/dl) occurred. These observations suggest that the intrauterine and postnatal anemia in fetuses who receive IUTs may be explained both by hemolysis of newly formed erythrocytes by circulating antibody, which typically persisted for more than a month after birth, and by suppressed erythropoiesis.

Effects of recombinant human erythropoietin in infants with the anemia of prematurity: a pilot study

In an attempt to stimulate endogenous erythrocyte production and thereby provide an alternative to erythrocyte transfusions, we administered recombinant human erythropoietin (rHuEpo) in doses of 75 to 300 units/kg/wk to seven infants with the anemia of prematurity. Treatment was started between 21 and 33 days of life, maintained for 4 weeks, and was well tolerated. All the patients had low baseline serum erythropoietin levels. After rHuEpo therapy, the number of reticulocytes increased from a mean baseline count of 75 x 10(9)/L to 95, 141, and 165 x 10(9)/L on days 7, 10, and 14 of therapy, respectively. Correction or stabilization of the anemia was observed in six of seven patients, whose estimated total erythrocyte volume increased by 49% during therapy (vs a predicted increment of 18% in the absence of rHuEpo). In one patient, however, the hematocrit declined during the treatment, and in three of the responders a secondary fall in hematocrit was noted either during therapy or after its discontinuation. Serum iron and ferritin levels rapidly decreased after the initiation of rHuEpo therapy, and in most patients transient early thrombocytosis and late neutropenia were observed. These data suggest that rHuEpo may correct or stabilize the anemia of prematurity. Its effects, however, may be limited by a variety of factors, among which iron availability probably plays an important role. Controlled studies will be needed to confirm these preliminary observations.