Comparison of red blood cell survival in sheep determined using red blood cells labeled with either biotin at multiple densities or [14C]cyanate: validation of a model to study human physiology and disease

BACKGROUND

Measurement of red blood cell (RBC) survival (RCS) is important for investigating pathophysiology and treatment of anemia. Our objective was to validate the multidensity biotin method for RCS determination in sheep, a commonly used model of RBC physiology. [(14) C]Cyanate served as the reference method for long-term RCS because the (51) Cr method (the reference method for humans) is not reliable in sheep.

STUDY DESIGN AND METHODS

Aliquots of autologous RBCs from eight adult sheep were labeled with [(14) C]cyanate and four separate densities of biotin (BioRBCs) and reinfused. Short-term RCS was assessed by posttransfusion recovery at 24 hours (PTR(24) ); long-term RCS was assessed by the time to 50% survival (T(50) ) and mean potential life span (MPL).

RESULTS

Values for PTR(24) of the four BioRBC densities were not different. Values for RCS as reflected by T(50) and MPL were nearly identical for [(14) C]cyanate and the two intermediate-density BioRBC populations. In contrast, the lowest-density BioRBC population survived slightly longer (p < 0.01), but with a difference of no clinical significance. The highest-density BioRBC population importantly shortened RCS (p < 0.01 compared to the two intermediate densities).

CONCLUSION

This study provides evidence that BioRBCs labeled at four biotin densities can be used to independently and simultaneously measure short-term RCS and that BioRBCs labeled at the three lowest biotin densities can be used to accurately and simultaneously measure long-term RCS. Because the sheep RBC model is comparable to humans, this nonradioactive method has promise for use in RBC kinetic studies in neonates and pregnant women.

One pathway to academic success: autobiography of Dr Ronald G. Strauss

Often, I have been asked by "junior faculty"-who are usually burdened by substantial responsibilities in service and teaching-how they can launch their career in research as a means to succeed in academic medicine. Obviously, the answers/solutions are as diverse as are the circumstances of each questioner. In the following article, I offer the approach that I applied to my career-acknowledging that "one shoe doesn't fit all" and that others will advise differently. However, one truism exists whenever one seeks excellence in anything-the opportunity must be present to commit uninterrupted time for thought/concentration, organization, training/mentoring/study, and effort/hard work. Without such an opportunity, success in research will be elusive.

Acute physiological effects of packed red blood cell transfusion in preterm infants with different degrees of anaemia

OBJECTIVE

The safe lower limit of haematocrit or haemoglobin that should trigger a red blood cell (RBC) transfusion has not been defined. The objective of this study was to examine the physiological effects of anaemia and compare the acute responses to transfusion in preterm infants who were transfused at higher or lower haematocrit thresholds.

METHODS

The authors studied 41 preterm infants with birth weights 500-1300 g, who were enrolled in a clinical trial comparing high ('liberal') and low ('restrictive') haematocrit thresholds for transfusion. Measurements were performed before and after a packed RBC transfusion of 15 ml/kg, which was administered because the infant's haematocrit had fallen below the threshold defined by study protocol. Haemoglobin, haematocrit, RBC count, reticulocyte count, lactic acid and erythropoietin were measured before and after transfusion using standard methods. Cardiac output was measured by echocardiography. Oxygen consumption was determined using indirect calorimetry. Systemic oxygen transport and fractional oxygen extraction were calculated.

RESULTS

Systemic oxygen transport rose in both groups following transfusion. Lactic acid was lower after transfusion in both groups. Oxygen consumption did not change significantly in either group. Cardiac output and fractional oxygen extraction fell after transfusion in the low haematocrit group only.

CONCLUSIONS

These study's results demonstrate no acute physiological benefit of transfusion in the high haematocrit group. The fall in cardiac output with transfusion in the low haematocrit group shows that these infants had increased their cardiac output to maintain adequate tissue oxygen delivery in response to anaemia and, therefore, may have benefitted from transfusion.

Anaemia of prematurity: pathophysiology and treatment

Most infants with birth weight <1.0 kg are given multiple red blood cell (RBC) transfusions within the first few weeks of life. The anaemia of prematurity is caused by untimely birth occurring before placental iron transport and fetal erythropoiesis are complete, by phlebotomy blood losses taken for laboratory testing, by low plasma levels of erythropoietin due to both diminished production and accelerated catabolism, by rapid body growth and need for commensurate increase in red cell volume/mass, and by disorders causing RBC losses due to bleeding and/or hemolysis. RBC transfusions are the mainstay of therapy with recombinant human erythropoietin largely unused because it fails to substantially diminish RBC transfusion needs--despite exerting substantial erythropoietic effects on neonatal marrow.

Red blood cell (RBC) volume can be independently determined in vivo in humans using RBCs labeled at different densities of biotin

BACKGROUND

Anemia is a serious problem in critically ill neonates. To investigate the pathophysiology of anemia and responses to red blood cell (RBC) transfusions and erythropoietin therapy, repeated measurement of red blood cell volume (RCV) and blood volume is useful. To extend our previous sheep study in which RBCs were labeled at four different biotin densities, we assessed the validity of this multidensity method for in vivo measurement of circulating RCV in humans.

STUDY DESIGN AND METHODS

In eight healthy adults, autologous RBCs were biotinylated at each of four biotin densities (6, 18, 54, and 162 µg biotinylation reagent/mL RBC), mixed, and infused intravenously; blood was sampled at 10, 20, and 60 minutes. At each time, RCV was calculated from dilution of individual RBC populations enumerated by flow cytometry. RCV measurements from the population of RBCs biotinylated at 6 µg/mL were chosen as the reference values because this density had been previously validated against the 51Cr method in vitro and in vivo in humans.

RESULTS

Values for RCVs were not significantly different among the four densities of biotinylated RBCs at any of the three time points and did not change over 60 minutes.

CONCLUSIONS

These studies provide evidence that four densities of biotinylated RBCs can be used in vivo for simultaneous, independent, accurate measurements of RCV in humans. We speculate that this method will also be useful for repeated measurement of RCV and blood volume in infants and other patient populations in whom radioactive labels should be avoided.

Red blood cell (RBC) volume can be independently determined in vivo in the sheep using ovine RBCs labeled at different densities of biotin

BACKGROUND

To investigate the pathophysiology of anemia and responses to red blood cell (RBC) transfusions and erythropoietin, repeated measurement of the circulating red blood cell volume (RCV) would be useful. Ovine erythropoiesis is similar to human erythropoiesis. Accordingly, a method for measuring RCV using either human or sheep RBCs labeled at different biotin densities has been previously validated in vitro. Here preclinical studies validating this method for in vivo measurement of circulating RCV in sheep are reported.

STUDY DESIGN AND METHODS

For each sheep, autologous RBCs were biotinylated were at four discrete densities (12, 24, 48, and 96µg biotinylation reagent/mL RBCs). The densities were mixed and infused intravenously. Blood was sampled five times over 1 hour beginning at 4 minutes. RCV values were determined based on dilution of each population of biotinylated RBCs and by the [(14) C]cyanate method.

RESULTS

There was no difference among RCVs measured at all densities through 16 minutes; however, by 60 minutes, RBCs biotinylated at the highest density overestimated RCV by 7.6%. RCV values increased 41% over the hour, consistent with equilibration with a pool of RBCs sequestered in the spleen. RCV by the [(14) C]cyanate method paralleled results by the biotin method but averaged 8% greater.

CONCLUSIONS

These studies provide evidence that all four densities of biotinylated RBCs can be used in sheep to simultaneously and independently determine RCV. We speculate that the multidensity biotinylation method will be useful both for multiple simultaneous measurements and for repeated measurement of circulating RCV and blood volume in humans.

Long-term outcome of brain structure in premature infants: effects of liberal vs restricted red blood cell transfusions

OBJECTIVE

To assess the long-term outcome of brain structure in preterm infants, at an average age of 12 years, who received a red blood cell transfusion for anemia of prematurity.

DESIGN

As neonates, this cohort of infants participated in a clinical trial in which they received red blood cell transfusions based on a high pretransfusion hematocrit threshold (liberal group) or a low hematocrit threshold (restricted group). These 2 preterm groups were compared with a group of full-term healthy control children.

SETTING

Tertiary care hospital.

PARTICIPANTS

Magnetic resonance imaging scans for 44 of the original 100 subjects were obtained.

INTERVENTION

Liberal vs restricted transfusion.

MAIN OUTCOME MEASURES

Intracranial volume, total brain tissue, total cerebrospinal fluid, cerebral cortex and cerebral white matter volume, subcortical nuclei volume, and cerebellum volume.

RESULTS

Intracranial volume was substantially smaller in the liberal group compared with controls. Intracranial volume in the restricted group was not different from controls. Whole-cortex volume was not different in either preterm group compared with controls. Cerebral white matter was substantially reduced in both preterm groups, more so for the liberal group. The subcortical nuclei were substantially decreased in volume, equally so for both preterm groups compared with controls. When sex effects were evaluated, the girls in the liberal group had the most significant abnormalities.

CONCLUSION

Red blood cell transfusions affected the long-term outcome of premature infants as indicated by reduced brain volumes at 12 years of age for neonates who received transfusions using liberal guidelines.

Red blood cell (RBC) survival determined in humans using RBCs labeled at multiple biotin densities

BACKGROUND

Safe, accurate methods permitting simultaneous and/or repeated measurement of red blood cell (RBC) survival (RCS) are important to investigate pathophysiology and therapy of anemia. Methods using chromium 51 ((51) Cr)-labeled RBCs are unacceptable for infants, children, and pregnant women. We report RCS measured in vivo using RBCs labeled with several densities of biotin (BioRBCs).

STUDY DESIGN AND METHODS

Aliquots of autologous RBCs from eight healthy adult subjects were labeled separately at four discrete biotin densities, mixed, and infused. The proportion of each population of BioRBCs circulating was determined serially by flow cytometry over 20 weeks. For each population, RCS was assessed by the following: 1) posttransfusion BioRBC recovery at 24 hours (PTR(24) ); 2) time to decrease to 50% of the enrichment at 24 hours (T(50) ); and 3) mean potential lifespan (MPL).

RESULTS

Among the four BioRBC densities, no significant differences in PTR(24) were observed. T(50) and MPL were similar for the two lowest BioRBC densities. In contrast, the two highest BioRBC densities demonstrated progressively decreased T(50) and MPL.

CONCLUSIONS

RBCs labeled at four biotin densities can be used to independently and accurately measure PTR(24 ) and two lowest biotin densities can accurately quantitate long-term RCS. This method provides a tool for investigating anemia in infants, fetuses, and pregnant women with the following advantages over the standard (51) Cr method: 1) study subjects are not exposed to radiation; 2) small blood volumes (e.g., 20 µL) are required; and 3) multiple independent RCS measurements can be made simultaneously in the same individual.

Dose of prophylactic platelet transfusions and prevention of hemorrhage

BACKGROUND

We conducted a trial of prophylactic platelet transfusions to evaluate the effect of platelet dose on bleeding in patients with hypoproliferative thrombocytopenia.

METHODS

We randomly assigned hospitalized patients undergoing hematopoietic stem-cell transplantation or chemotherapy for hematologic cancers or solid tumors to receive prophylactic platelet transfusions at a low dose, a medium dose, or a high dose (1.1x10(11), 2.2x10(11), or 4.4x10(11) platelets per square meter of body-surface area, respectively), when morning platelet counts were 10,000 per cubic millimeter or lower. Clinical signs of bleeding were assessed daily. The primary end point was bleeding of grade 2 or higher (as defined on the basis of World Health Organization criteria).

RESULTS

In the 1272 patients who received at least one platelet transfusion, the primary end point was observed in 71%, 69%, and 70% of the patients in the low-dose group, the medium-dose group, and the high-dose group, respectively (differences were not significant). The incidences of higher grades of bleeding, and other adverse events, were similar among the three groups. The median number of platelets transfused was significantly lower in the low-dose group (9.25x10(11)) than in the medium-dose group (11.25x10(11)) or the high-dose group (19.63x10(11)) (P=0.002 for low vs. medium, P<0.001 for high vs. low and high vs. medium), but the median number of platelet transfusions given was significantly higher in the low-dose group (five, vs. three in the medium-dose and three in the high-dose group; P<0.001 for low vs. medium and low vs. high). Bleeding occurred on 25% of the study days on which morning platelet counts were 5000 per cubic millimeter or lower, as compared with 17% of study days on which platelet counts were 6000 to 80,000 per cubic millimeter (P<0.001).

CONCLUSIONS

Low doses of platelets administered as a prophylactic transfusion led to a decreased number of platelets transfused per patient but an increased number of transfusions given. At doses between 1.1x10(11) and 4.4x10(11) platelets per square meter, the number of platelets in the prophylactic transfusion had no effect on the incidence of bleeding. (ClinicalTrials.gov number, NCT00128713.)

2008 Emily Cooley Memorial Lecture: lessons learned from pediatric transfusion medicine clinical trials . . . a little child shall lead them

BACKGROUND

Many clinical practices in transfusion medicine are controversial and/or lack definitive guidelines established by sound clinical trials. Although recommendations based on results of clinical trials performed using infants and children may not always be applied directly to adults--and vice versa--lessons learned from pediatric trials can be useful when critically assessing the design/results/conclusions of adult trials.

STUDY DESIGN AND METHODS

Four randomized clinical trials (RCTs) studying pediatric patients were critically reviewed. They addressed two red blood cell (RBC) transfusion issues: 1) transfusion guidelines by which RBC transfusions are "triggered" by liberal (LIB; high pretransfusion patient hematocrit [Hct] levels) versus being "triggered" by restricted (RES; low pretransfusion Hct levels) and 2) transfusion of fresh RBCs (<or=7 days' storage) versus RBCs (up to 42 days' storage).

RESULTS

Findings established by primary outcomes generally were firm (e.g., fewer RBC transfusions were given to infants/children managed by RES guidelines; transfusing small volumes of RBCs stored up to 42 days to preterm infants diminished allogeneic donor exposures and were equally efficacious and safe as fresh RBCs stored <or=7 days). Findings based on secondary outcomes, subset, and post hoc analyses were inconsistent (e.g., clinical outcomes were equivalent after LIB or RES transfusions in only two of three RCTs; in the third, more neurologic problems were found in neonates given RES transfusions).

CONCLUSIONS

Clinical practices should be based on data pertaining to the primary outcomes of RCTs, because trials are designed and statistically powered to address these issues. Clinical practices suggested by analysis of secondary outcomes, subsets of patients, and post hoc analyses should be applied cautiously until studied further-ideally, as primary outcomes in subsequent RCTs.

Red blood cell volume can be independently determined in vitro using sheep and human red blood cells labeled at different densities of biotin

BACKGROUND

The development of valid methods for repeatedly measuring red blood cell (RBC) volume (RCV) in the same individual would be useful in furthering understanding of the physiology and pathophysiology of the pregnant woman, fetus, and infant under a variety of conditions.

STUDY DESIGN AND METHODS

Small volumes (5 to 100 mL) of either sheep or human blood were used to test the hypothesis that there is no significant difference in RCV and blood volume determined in vitro using as many as five populations of RBCs labeled at distinct biotin densities. By varying the mass of biotinylating reagent, the density of biotin on the surface of RBCs was incrementally increased to produce discrete populations as assessed by flow cytometric enumeration. Calculation of RCV for each biotin-labeled RBC population was based on the dilution principle.

RESULTS

All biotin densities, except the most densely labeled, where variance was the greatest, accurately quantitated the in vitro blood volume to within 10 percent of the correct value. There was no bias of either overestimation or underestimation in the determination of the blood volume using either sheep or human RBCs.

CONCLUSION

These in vitro results provide evidence that the multidensity biotin labeling method is sufficiently accurate to utilize in vivo for repeated determination of circulating RCV and blood volume.

Red cell volume can be accurately determined in sheep using a nonradioactive biotin label

The sheep has served as an informative animal model for investigation of human fetal and newborn erythropoiesis and red blood cell (RBC) kinetics. We previously validated the permanent label (14C)cyanate for measuring red cell volume (RCV) in sheep. Here, we validate biotin labeling of RBCs as a nonradioactive method for measuring RCV in sheep with the anticipation that it can be applied in studies of human infants. The RCV was determined simultaneously using two techniques for quantitation of the biotin label. The first one quantified total blood concentration of biotin label on biotin-labeled RBCs using (125I)streptavidin. The second one enumerated biotin-labeled RBCs by flow cytometry after incubation with fluorescein-conjugated avidin. RCV measurements made using the two biotin quantitation techniques were validated against both (14C)cyanate and 51Cr as reference methods. Both biotin techniques produced RCV values that agreed well with the reference methods and with each other, producing correlation coefficients averaging >or =0.93. Sequential repetitive measurements in the same animal also agreed with the (14C)cyanate method and each other (average difference <10%). These results establish biotin-labeled RBCs as an accurate method for performing RCV measurements in sheep. This biotin method can be applied in studies that model neonatal erythropoiesis.