Key points

Introduction

Pediatric patients with malignancies or benign hematologic diseases are a heterogeneous group with complicated underlying pathophysiologies leading to their requirements for transfusion therapy. Their ages range from preterm and term neonates, infants, young children, and adolescents, and each of these age groups has unique transfusion requirements. The focus of this review is on transfusion therapies in pediatric patients with hypoproliferative cytopenias, particularly secondary to chemotherapy, hematopoietic stem cell transplant (HSCT), congenital cytopenias, and aplastic anemia ( Table 1 ).

Introduction

Pediatric patients with malignancies or benign hematologic diseases are a heterogeneous group with complicated underlying pathophysiologies leading to their requirements for transfusion therapy. Their ages range from preterm and term neonates, infants, young children, and adolescents, and each of these age groups has unique transfusion requirements. The focus of this review is on transfusion therapies in pediatric patients with hypoproliferative cytopenias, particularly secondary to chemotherapy, hematopoietic stem cell transplant (HSCT), congenital cytopenias, and aplastic anemia ( Table 1 ).

Epidemiology of transfusions in pediatric patients

Overall, pediatric patients are the recipients of 1.1% of plasma, 2.1% of red blood cells (RBC), and 4.8% of platelet transfusions in the United States, which translates to 425,000 units transfused to children in 2011. In adult patients, RBCs and plasma (thawed, fresh frozen [FFP], or plasma frozen) are the 2 most commonly transfused components followed by platelets, cryoprecipitate, and granulocytes. RBCs and platelets are the most commonly transfused components in pediatric patients. Slonim and colleagues published a study using the Pediatric Health Information System data set for transfusion information for more than 1,000,000 pediatric hospital discharges that occurred between 1997 and 2004. This study found approximately 5% of all patients received one or more transfusions during their hospitalization. Neonates (<30 days of age) received 17.5% of the transfusions. According to a single-center retrospective review at an academic tertiary care pediatric hospital, the most commonly transfused patients are those undergoing cardiac surgery (22% of the cohort), premature neonates (21.6%), patients with malignancies (10.9%), and patients with benign hematologic disorders (9.6%).

The complication rate in pediatric patients is approximately 6.2 to 10.7 per 1000 units transfused. At a single institution, the rate of complications in pediatric patients was 2.6 times higher than that in adult patients. Pediatric patients were more likely to develop allergic reactions (2.7/1000 vs 1.1/1000 transfusions), febrile nonhemolytic reactions (1.9/1000 vs 0.47/1000 transfusions), and hypotensive reactions (0.29/1000 vs 0.078/1000 transfusions). Hemovigilance data should be interpreted with caution because of differences in reporting frequency, but it is important to consider the developmental and underlying disease differences between pediatric and adult transfusion recipients.

Red blood cell transfusions

RBC transfusions are an integral part of the supportive care for patients with anemia due to bone marrow suppression or failure; however, there have been few randomized, controlled trials (RCTs) designed to investigate optimal RBC transfusion strategies. The only randomized, controlled RBC transfusion trials performed in pediatric patients have evaluated the difference in transfusions and outcomes in neonates and critically ill children. In critically ill children, a restrictive transfusion strategy (hemoglobin ≤7 g/dL) resulted in fewer patients receiving transfusions than a liberal strategy (≤9.5 g/dL; 46% vs 98%, P <.001); however, among those children transfused, there was no difference in the number of units transfused (1.9 ± 3.4 vs 1.7 ± 2.1 units per patient, P = .24). There was no difference in morbidity in the 2 cohorts.

In contrast, a retrospective study of pediatric HSCT patients at a single institution demonstrated that a lower threshold of a hemoglobin of 7 g/dL did not decrease the number of transfused patients compared with the cohort of patients with a threshold of 9 g/dL (96% vs 98.5%, respectively; P = .38). Patients with the lower transfusion threshold received fewer transfusions (median = 3, interquartile range [2–5] vs 4 [3–8], P = .002), which was associated with approximately $1,400 saving in transfusion-related charges. There was no difference in time to engraftment, length of hospital stay, or 100-day mortality, although it is unclear whether this study was sufficiently powered for these outcomes.

A recent Cochrane Database Review summarized 19 RCTs that compared restrictive and liberal transfusion strategies in myriad patient populations; only one included adults undergoing HSCT or leukemia therapy. This pilot study of 60 adults was designed to investigate whether a liberal transfusion threshold of 12 g/dL of hemoglobin would result in decreased bleeding compared with a restrictive transfusion threshold of 8 g/dL. This pilot study was not powered to evaluate outcomes such as number of RBC transfusions or bleeding incidence, but showed that such a trial would be feasible and safe to perform as a large, multi-institutional RCT.

Based on this pilot study and previous studies in children with leukemia and murine models, which showed high hemoglobin levels were associated with faster neutrophil recovery, a trial comparing a hemoglobin threshold of 7 versus 12 g/dL was designed for pediatric patients undergoing HSCT. However, this trial was stopped after enrolling only 6 patients (3 per arm) when all 3 patients in the 12-g/dL arm developed severe veno-occlusive disease (VOD). Not only was the incidence significantly higher in the experimental arm than in the control arm but also the severity of the VOD was higher than historic controls. It is possible that the increased blood viscosity could have decreased sinusoidal blood flow, increasing risk of VOD. Also, the patients in the experimental arm received dramatically more RBC transfusions (3, 9, and 14 vs 2, 1, and 1) than patients in the control arm. Therefore, it is also possible that the RBC transfusions directly contributed to VOD development through the introduction of inflammatory cytokines and RBC microvesicles.

The investigators of this RCT recommend continuing to use the lower transfusion threshold of 7 g/dL, which agrees with what many pediatric oncologists and HSCT physicians report doing. In a 2005 survey of members of the American Society for Pediatric Hematology/Oncology (ASPHO) who reside in the United States, Wong and associates found that 56% of pediatric oncologists used a threshold of 7 g/dL or less and 42% used 8 g/dL or less. A survey of HSCT directors at institutions in the Children’s Oncology Group revealed that 25% report using a threshold of 7 g/dL or less and 60% use 8 g/dL or less. These responses suggest consistency among practitioners in uncomplicated patients; however, practice varies widely in different clinical situations. For example, in a child with neutropenic fever and tachypnea, approximately 5% of respondents would automatically transfuse at a hemoglobin 7 g/dL or less, 34% would use a threshold of 8 g/dL, 20% would transfuse at a hemoglobin 9 g/dL or less, and 42% would transfuse even if the hemoglobin was greater than 9 g/dL. Among hematologists managing patients with aplastic anemia, 50% report transfusing to maintain a hemoglobin greater than 6 to 8 g/dL and 31% only transfuse symptomatic patients.

Patients undergoing radiation therapy represent a unique challenge with respect to appropriate hemoglobin threshold during treatment. In fact, 48% of respondents report transfusing patients undergoing radiation therapy to maintain a hemoglobin greater than 9 g/dL. This practice stems from reports that patients with head and neck and gynecologic malignancies with low hemoglobin before and during radiation therapy had decreased survival compared with those without anemia. However, subsequent phase III trials that used either erythropoiesis-stimulating agents (ESAs) or RBC transfusions to correct anemia in patients undergoing radiation therapy showed that low hemoglobin was associated with decreased survival; however, anemic patients who received ESAs or transfusions actually fared worse than patients in the control arm. It is likely that the degree of anemia in these patients is associated with disease severity and therefore portends a poor prognosis and that correction of the anemia fails to mitigate the risk of relapse or progression. There has been one retrospective study published in pediatric patients with central nervous system (CNS) tumors that found hemoglobin less than 10 g/dL during radiation therapy was not associated with local recurrence and overall survival.

Another treatment-related morbidity associated with RBC transfusions is iron overload. Liver iron levels as measured by MRI and serum ferritin are directly correlated with volume of RBCs received during treatment. Therefore, patients who have received the most intense therapy for the longest duration are at the highest risk of iron overload. This finding is particularly true in patients with high-risk or relapsed cancer who undergo chemotherapy before HSCT. Bae and associates found that in children undergoing tandem autologous HSCTs for neuroblastoma, a dose of CD34+ cells was inversely correlated with both volume of RBCs transfused in the aftertransplant period as well as serum ferritin levels. Because of confounders such as disease severity and treatment length and intensity, it can be difficult to isolate the role that iron overload plays in treatment-related morbidity and mortality.

For many patients, once treatment is complete or engraftment after HSCT occurs, RBC transfusions are no longer needed so the expectation is that as these children grow and develop iron levels will decrease. One study found that the ferritin level of most patients decreased to less than 1000 μg/L within 1 year following their last transfusion; however, in a small minority of patients, elevated serum ferritin persisted more than 3 years after their last transfusion. Another small study found persistently elevated liver iron levels as detected by MRI over a year since the patients’ last transfusions.

These myriad studies suggest that a restrictive transfusion strategy, which is commonly used in pediatric hematology, oncology, and HSCT patients not only reduces number of transfusions but also may be associated with decreased morbidity and mortality. Patients undergoing HSCT for sickle cell disease have unique RBC transfusion needs; routine practice includes maintaining hemoglobin S percent less than 30% during the pretransplant preparation phase and to maintain a hemoglobin greater than 9 g/dL aftertransplant until RBC engraftment occurs.

In addition to transfusion threshold, dosage of RBCs is another issue. The recommendation for dosing in young children is 10 to 15 mL/kg, but in older children, like adult patients, there is the option for single-unit versus double-unit transfusions. A study of 139 adult oncology patients demonstrated that a single-unit policy reduced RBC transfusions by 25% and did not increase transfusion frequency. Similar studies need to be performed in adolescents.

Although a liberal transfusion strategy may be associated with adverse outcomes in pediatric patients as evidenced by the small study that found transfusing to maintain a hemoglobin greater than 12 g/dL was associated with adverse outcomes in patients undergoing HSCT (realizing that a threshold of 7–8 g/dL is commonly used), there are additional factors that should be considered in pediatric patients. The National Heart, Lung, and Blood Institute has recognized that multicenter RCTs are needed to better understand the impact that RBC transfusion threshold has on outcomes such as quality of life, growth and development in young children, incidence of bleeding events, impact on the immune system and incidence of infections, return of hematopoiesis, and event-free and overall survival. These trials can be incorporated into cancer treatment trials to better understand the unique needs of patients receiving different treatment regimens.

Platelet transfusions

Bleeding is a common complication in patients with hypoproliferative thrombocytopenia. Given risks for HLA alloimmunization and other adverse effects of platelet transfusions, reducing unnecessary transfusions without increasing bleeding risk is a priority. There have been numerous trials to investigate optimal platelet transfusion strategies to minimize bleeding risk. Only one of these trials, the Platelet Dose (PLADO) trial, included pediatric patients, which investigated whether a dose of 1.1 × 10 ¹¹ , 2.2 × 10 ¹¹ , and 4.4 × 10 ¹¹ platelets per square meter per transfusion would have an impact on bleeding incidence. This study used a prophylactic transfusion threshold of 10,000 platelets/μL for all patients. Overall, in the 1272 patients who received a platelet transfusion, the incidence of at least one clinically significant bleeding episode was about 70% in all treatment cohorts.

In a subgroup analysis of the 200 patients 18 years of age or younger, pediatric patients were found to have a significantly increased incidence of bleeding compared with adults. Bleeding incidence was inversely correlated with age: 86%, 88%, 77%, and 67%, for ages 0 to 5, 6 to 12, 13 to 18, and 19 years and older, respectively ( P <.001). In fact, among pediatric patients, those aged 0 to 5 undergoing autologous stem cell transplant had the highest incidence of bleeding (93%). These findings highlight the importance of performing high-quality RCTs in pediatric patients and not merely extrapolating data from adult trials to pediatric patients. Of the 2 studies that investigated a prophylactic transfusion threshold of 10,000/μL compared with a therapeutic transfusion-only strategy in patients 16 years old and older, autologous transplant patients had a significantly lower incidence of clinically significantly bleeding than patients being treated for a hematologic malignancy (with either chemotherapy or allogeneic HSCT). Of note, both of these trials found that patients on a therapeutic transfusion-only regimen had a higher incidence of bleeding compared with those receiving prophylactic platelet transfusions.

Although this study found no difference in bleeding incidence between the different dosage cohorts, subjects who received a higher dose of platelets overall received fewer platelet transfusions: 3.6 platelet transfusions per person in the high-dose group compared with 4.5 and 6.1 transfusions per person in the medium- and low-dose groups, respectively. There was also a longer time between transfusions: median of 2.9 days in the high-dose group compared with 1.9 and 1.1 days in the medium- and low-dose groups, respectively ( P <.001). Current recommendations for platelet dose are 10 to 15 mL/kg of body weight. The data from the PLADO trial suggest that patients for whom dosing at the higher end of this range may have a longer interval between transfusions and receive fewer transfusions, which reduces donor exposures. These data also suggest that there is little benefit to transfusing more than a single apheresis donor unit as a method of decreasing bleeding risk.

All of the platelet transfusion trials in both pediatric and adult patients have been performed in the inpatient setting. Outpatient management of hypoproliferative thrombocytopenia is not well-studied, although most providers use a threshold of 10,000 or 20,000/μL. In a survey of pediatric oncologists, 54% of respondents reported using a prophylactic transfusion threshold of 10,000/μL and 42% reported using 20,000/μL. Similarly, 44% of pediatric HSCT directors reported using a prophylactic threshold of 10,000/μL and 47% use 20,000/μL. In a survey of 18 children’s hospitals who care for patients with aplastic anemia, 91% of respondents reported using a prophylactic platelet transfusion threshold of 10,000/μL, whereas 64% use 20,000/μL as the threshold in patients receiving antithymocyte globulin and 28% use a threshold between 30 and 50,000/μL. In general, a platelet transfusion threshold of 10,000 to 20,000/μL in stable patients with hypoproliferative thrombocytopenia minimizes both bleeding risk and exposure to platelet transfusions. One notable exception to this group is children and young adults undergoing HSCT for sickle cell disease, who have an increased risk of neurologic complications in the after-transplant period. In a case series of 28 pediatric patients, 3 patients developed intracranial hemorrhage, and in 2 cases, this bleeding was fatal. All 3 of these patients had a history of stroke before transplant, indicating this is a particularly high-risk group. In the after-transplant time period, platelet count should be maintained greater than 50,000/μL in order to minimize risk of hemorrhagic stroke.

Although there appears to be consensus for management of stable thrombocytopenic patients, there are significant variability and little data regarding transfusion practices for patients undergoing a procedure such as bone marrow biopsy or lumbar puncture. Of the respondents from the ASPHO survey, for patients undergoing a lumbar puncture, 8% would use a threshold of less than 10,000/μL, 26% would use a threshold less than 20,000/μL, 48% would transfuse if the platelet count were between 25 and 50,000/μL, and 19% would transfuse if platelets were less than 50,000/μL. The rate of severe complications (eg, spinal subdural hematoma or spontaneous hemorrhage) in children undergoing lumbar puncture is quite low, even at platelet counts of less than 20,000/μL. However, traumatic lumbar puncture occurs at a rate of 10% to 29%, and in patients with circulating peripheral blasts, this can adversely affect progression-free survival and increase risk of CNS relapse.

There are many variables that can have an impact on risk of traumatic lumbar puncture, including patient age, race, and body mass index; provider experience; and time since previous lumbar puncture. Platelet count is inversely correlated with the risk of traumatic lumbar puncture. In multivariable regression models, platelet counts 0 to 25,000/μL, 26,000 to 50,000/μL, 51,000 to 75,000/μL, and 76,000 to 100,000 had an odds ratio (OR) of 1.8, 1.4, 1.5, and 1.4 compared with platelet counts greater than 100,000/μL were associated with increased risk of traumatic and blood lumbar punctures. Shaikh and colleagues found a similar risk in patients with a platelet count less than 100,000/μL. An important note of these studies is that, in general, there was no difference in risk of traumatic lumbar puncture, if the platelet count was between 20,000 and 30,000/μL and 100,000 μL.

Although there are associations between platelet count less than 100,000/μL and risk of traumatic lumbar puncture and between traumatic lumbar puncture with circulating blasts and risk of CNS relapse, there have been no studies performed that have found a direct link between platelet count at the time of initial lumbar puncture and event-free survival. In newly diagnosed patients with leukemia who often present profoundly thrombocytopenic, it may be difficult to increase their platelet count greater than 100,000/μL, and doing so may cause fluid overload and delay diagnosis and treatment initiation. Therefore, the decision to transfuse a patient before lumbar puncture to achieve a specific platelet count should be made on an individual basis that considers the other risk factors associated with traumatic or bloody lumbar puncture and the patient’s underlying disease.