Core Concepts the Biology of Hemoglobin

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DOI: 10.1542/neo.12-1-e29 2011;12;e29-e38 NeoReviews Robin K. Ohls Core Concepts: The Biology of Hemoglobin http://neoreviews.aappublications.org/cgi/content/full/neoreviews;12/1/e29 located on the World Wide Web at: The online version of this article, along with updated information and services, is Online ISSN: 1526-9906. Illinois, 60007. Copyright © 2011 by the American Academy of Pediatrics. All rights reserved. by the American Academy of Pediatrics, 141 Northwest Point Boulevard, Elk Grove Village, it has been published continuously since 2000. NeoReviews is owned, published, and trademarked NeoReviews is the official journal of the American Academy of Pediatrics. A monthly publication, by Sreeram Subramanian on February 28, 2011 http://neoreviews.aappublications.org Downloaded from

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Page 1: Core Concepts the Biology of Hemoglobin

DOI: 10.1542/neo.12-1-e29 2011;12;e29-e38 NeoReviews

Robin K. Ohls Core Concepts: The Biology of Hemoglobin

http://neoreviews.aappublications.org/cgi/content/full/neoreviews;12/1/e29located on the World Wide Web at:

The online version of this article, along with updated information and services, is

Online ISSN: 1526-9906. Illinois, 60007. Copyright © 2011 by the American Academy of Pediatrics. All rights reserved. by the American Academy of Pediatrics, 141 Northwest Point Boulevard, Elk Grove Village,it has been published continuously since 2000. NeoReviews is owned, published, and trademarked NeoReviews is the official journal of the American Academy of Pediatrics. A monthly publication,

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Core Concepts: The Biology of HemoglobinRobin K. Ohls, MD*

Author Disclosure

Dr Ohls has disclosed

no financial

relationships relevant

to this article. This

commentary does not

contain a discussion

of an unapproved/

investigative use of a

commercial

product/device.

AbstractA consistent and organized transition from embryonic to fetal to adult hemoglobin(Hgb) occurs during human fetal development. Hgb concentrations gradually in-crease, averaging 18 g/dL (180 g/L) by 40 weeks’ gestation. The ability to deliveroxygen to tissues in the fetus and neonate is primarily determined by the percentage offetal versus adult Hgb and the concentration of 2,3 diphosphoglycerate (2,3-DPG).Studies continue to evaluate the relationship between Hgb concentrations and oxygendelivery in neonates to determine what Hgb concentrations best meet the needs of awide variety of clinical situations from the critically ill extremely low-birthweightinfant to the stable growing preterm infant. Biochemical interactions between nitricoxide (NO) and Hgb beyond the production of methemoglobin do occur and may bea source of deliverable NO to the microcirculation under hypoxic conditions.

Objectives After completing the article, readers should be able to:

1. Describe the development of globin gene synthesis and Hgb formation.2. Explain fetal to neonatal transition of Hgb F to Hgb A.3. Review the development and function of 2,3-DPG.4. Describe the relationship between NO and Hgb.

Hemoglobin Concentration During DevelopmentRed blood cell indices such as Hgb, hematocrit, mean cell volume, and red cell distributionwidth change during gestation and continue to change through the first postnatal year. (1)Hgb concentrations gradually rise during gestation. At 10 weeks’ gestation, the averageconcentration is approximately 9 g/dL (90 g/L); (1)(2) by the start of the third trimester,values in the developing fetus reach 11 to 12 g/dL (110 to 120 g/L); and by 30 weeks,Hgb concentrations are 13 to 14 g/dL (130 to 140 g/L). (1) Jopling and associates (3)have identified reference ranges based on approximately 25,000 preterm and term infants.From 22 to 40 weeks’ gestation, there is a consistent increase in Hgb of 0.21 g/dL(2.1 g/L) per week (Fig. 1). (3) In this large cross-sectional study, no sex differences werenoted in Hgb concentrations, but some studies have reported a slight difference in Hgbconcentrations between white and African American preterm infants. (4) At delivery, a 1-to 2-g/dL (10- to 20-g/L) rise in Hgb may result from transfusion of placental blood intothe infant. In term and late preterm infants, Hgb concentrations increase by approximately4% at 4 hours of postnatal age, resulting from a decrease in plasma volume. (5) By 8 to12 hours of age, Hgb concentrations achieve a relatively constant level. In contrast, in anevaluation of more than 20,000 preterm infants (29 to 34 weeks’ gestation), a decrease ofapproximately 6% was measured at 4 hours of age. (3) This decrease might be due to a lackof placental transfusion because the umbilical cord in preterm infants is rapidly clamped toexpedite resuscitation.

Red blood cell production decreases significantly after birth, primarily as a result of theincreased availability of oxygen, which greatly reduces erythropoietin (Epo) productionand endogenous erythropoiesis. By the end of the first postnatal week, Hgb concentrationsbegin to decline (3) and continue to decrease over the next several weeks as a result ofdecreased erythrocyte production, a shortened erythrocyte life span, and an increase in

*Professor of Pediatrics, University of New Mexico, Albuquerque, NM.

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blood volume related to growth (Fig. 2). Term infantsreach their Hgb nadir at approximately 8 weeks, withan average Hgb concentration of 11.2 g/dL (112 g/L).(6) Hgb concentrations subsequently rise so that by6 months, the concentration averages 12.1 g/dL(121 g/L). (7)

The decline in Hgb in very low-birthweight infants isgreater than that in term infants, in part because ofphlebotomy losses and in part because of the suppressiveimpact of transfusions on endogenous erythropoiesis.Such infants reach the Hgb nadir of 8 g/dL (80 g/L)at 4 to 8 weeks of age. (8) Figure 2 demonstratesrelationships among birthweight, chronologic age, andHgb in term and preterm infants. (3)

Maternal conditions can influence fetal Hgb concen-trations. Infants born small for gestational age can havehigher Hgb concentrations due to placental insufficiencyand secondary polycythemia. (9)(10) Infants of dia-betic mothers, infants of smoking mothers, and infantsborn at higher altitudes also tend to have higher Hgbconcentrations at birth (11)(12)(13)(14) In all of theseconditions, accelerated erythropoiesis is believed to bepart of a compensating mechanism designed to raiseoxygen-carrying capacity to maintain an adequate oxy-gen supply to the fetus. In the case of the fetus of amother who has diabetes, increased metabolic demandsof the fetus (as evidenced by a positive correlation be-tween maternal Hgb A1c and neonatal Hgb) may ac-

count for the higher oxygen needsand the compensatory increase inerythropoiesis and Hgb concentra-tion. (15)

Hemoglobin SynthesisDuring fetal erythropoiesis, an or-derly evolution of the productionof various Hgbs occurs. Eight glo-bin genes direct the synthesis of sixdifferent polypeptide chains, desig-nated alpha (�), beta (�), gamma(�), delta (�), epsilon (�), and zeta(�). These globin chains combinein the developing erythroblast toform seven different Hgb tetramers:Gower 1 (�2-�2), Gower 2 (�2-�2),Portland (�2-�2), fetal hemoglobin(Hgb F: �2-�2), and two types ofadult hemoglobin: �2-�2, known asHgb A, and �2-�2, known as HgbA2 (Table 1).

Globin GenesThe globin genes are organized into two clusters(Fig. 3). The �-like genes are located along a 20-kb distalsegment of the short arm of chromosome 16. The clustercontains three functional genes (�1, �2, and �2), threepseudogenes (evolutionary remnants of genes that arenot expressed because of inactivating mutations thatprevent production of a functional globin protein), andone gene of undetermined function (a globin-like genewithout inactivating mutations). The �-like gene clusteris located along a 60-kb segment of the short arm ofchromosome 11, and it contains five functional genes(�, �, A�, G�, and �) and one pseudogene. Within eachcomplex, the genes are all in the same 5� to 3� orienta-tion, and they are arranged in the order in which they areexpressed during development. (16)

Timing of Globin Chain SynthesisGlobin chain production has been determined at eachstage of development, from initial yolk sac (primitive) tohepatic (definitive) and marrow erythropoiesis. It is notclear why or how primitive erythroid progenitors pro-grammed to produce embryonic Hgb transition to de-finitive progenitors programmed to produce Hgb F.Because quantification of globin gene expression usingreal time polymerase chain reaction methods reflectsproduction by a heterogeneous source of erythrocytes,production of a specific Hgb is usually reported as a

Figure 1. Reference ranges for blood hemoglobin concentrations at birth in 24,416patients at 22 to 42 weeks’ gestation. The solid line represents the mean value and thedashed lines represent the 5% to 95% reference range. Reprinted with permission fromJopling. (3)

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percentage of the total Hgb measured. Studies measur-ing Hgb production by erythroid colonies in cultureshow that individual cells in a colony produce predomi-nantly one type of Hgb. (17)

During the fourth to fifth week of gestation, �, �, and� chains are the primary globin chains produced (Fig. 4).

During the sixth to seventh week ofgestation, primitive erythroblastscontinue to produce �, �, and �

chains, while definitive erythrocytesproduce �, �, G�, and A� chains. Bythe seventh to eighth week, �- and�-chain synthesis is no longer de-tectable, and the primary globinchains produced are �, G�, and A�.�-chain production is just barelydetectable at this time and gradu-ally increases, comprising up to 10%of total non–�-chain production by10 weeks of gestation. (18) Geneticdisorders associated with �-chainsynthetic or structural abnormali-ties may be detected in utero assoon as �-chain production occursbut are often not clinically apparentuntil after birth.

From 10 to 33 weeks of gesta-tion, the primary globin chains syn-thesized are �, G�, A�, and �. As-sessment of the output of the twolinked �-globin genes by mRNAanalysis suggests that they are ex-pressed in the ratio (�2:�1) rang-ing from 1.5 to 3.0:1 throughoutfetal life, and this ratio continuesthrough normal adulthood. Therelative rates of G�-chain and A�-chain production are also constantthroughout fetal life at a G�:A� ratioof approximately 3:1. (19) Duringthe transition from 32 to 36 weeksof gestation, the relative rate of�-chain synthesis increases and thatof �-chain production declines, soat birth, �-chain synthesis makesup approximately 50% of non–�-chain synthesis. There is consider-able variation among infants, how-ever, with many infants showingprolonged dependence on Hgb F.After birth, the level of �-chain pro-

duction increases, while the level of �-chain productionsteadily declines, so by the end of the first year, �-chainsynthesis reaches the low concentration that is character-istic of adult life (�2%). Over the first few months afterbirth, the G�:A� ratio changes from 3:1 to 2:3, althoughthis ratio varies in adults. (20)(21)(22)

Figure 2. Reference ranges for blood hemoglobin concentrations in 39,559 patientsduring the 28 days after birth in late preterm and term infants 35 to 42 weeks’ gestation(panel A) and in preterm infants 29 to 34 weeks’ gestation (panel B). The solid linerepresents the mean value and the dashed lines represent the 5% to 95% reference range.Reprinted with permission from Jopling. (3)

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Delta-chain production has been observed as early as32 weeks’ gestation. Delta-gene production lags behind�-gene production, so the adult �/� synthesis ratio is notreached until 4 to 6 months after birth.

Hemoglobin Production During DevelopmentDevelopmental changes in the production of Hgb can beseen in Figure 5. Before the onset of other chain forma-tion, unpaired globin chains may form tetramers, result-

ing in the presence of �4. (23) Soon thereafter, �- and�-chain production begins, and Hgb Gower 1 (�2-�2),Gower 2 (�2-�2), and Portland (�2-�2) are formed. (24)By 5 to 6 weeks’ gestation, Hgb Gower 1 and Gower 2constitute 42% and 24% of the total Hgb, respectively,with Hgb F (�2-�2) making up the remainder. By 14 to16 weeks, Hgb F constitutes 50% of the total Hgb, andby 20 weeks, it forms more than 90% of the Hgb. (25)Small quantities of Hgb A (�2-�2) are found beginningat 6 to 8 weeks’ gestation. The increase in �-chainproduction occurring between 12 and 20 weeks’ gesta-tion accounts for the sudden rise in Hgb A found atthe end of the first trimester of pregnancy. Tetramers of�-chains (�4 or Hgb Barts) and �-chains (�4 or Hgb H)can be found in conditions in which �-chain synthesis isimpaired or absent, such as �-thalassemia syndromes.

Hgb F is easily distinguished immunologically and bio-chemically from Hgb A. The primary differentiating physi-ologic characteristic of Hgb F is its decreased interactionwith 2,3-DPG (also known as 2, 3 bisphosphoglycerate).2,3-DPG binds to deoxyhemoglobin in a cavity betweenthe �-chains and stabilizes the deoxy form of Hgb, resultingin reduced Hgb-oxygen affinity. 2,3-DPG binds less effec-tively to �-globin chains because of the differing amino acid

sequence in the non–�-chain. Con-sequently, 2,3-DPG does not reducethe oxygen affinity of Hgb F as muchas that of Hgb A.

Fetal and adult Hgb also differ insolubility. Hgb F is more soluble instrong phosphate buffers than Hgb Aand is oxidized to methemoglobinmore easily than Hgb A. Hgb F has aconsiderably greater affinity for oxy-gen as a result of differences in bind-ing to 2,3-DPG mentioned previ-ously. Hgb F is resistant to acidelution, which allows differentiationof cells containing Hgb F from cellscontaining Hgb A. (26) This prop-erty forms the basis of differentiatingfetal from maternal red cells using theKleihauer Betke stain.

G�-chains represent 70% to 80%of the total �-chains in the blood ofthe fetus and newborn. The percentof �-chains made up of G� falls toabout 40% by 5 months of age. Thisunique difference in G�-chain pro-duction found in the fetus helps todistinguish fetal hematopoiesis from

Figure 3. Organization of the globin genes. Transcription takes place from the 5� to the 3�end; for both chromosomes, the genes are arranged in order of their developmental activation.The upper part of the figure represents the beta-like globin genes on the short arm ofchromosome 11, and the lower part of the figure represents the alpha-like genes on the distalshort arm of chromosome 16. Regions of the gene that code for primary globin proteins areshown as shaded ovals. Regions that code for pseudogenes (y-nonexpressed remnants thathave a number of inactivating mutations that prevent transcription and translation intofunctional globin protein) are shown as open ovals. �-1 is a globin-like gene withoutinactivating mutations. The locus control region (LCR) is shown as a hatched segment.

Table 1. Globin Chain Compositionof Common Hemoglobin

Type of Hemoglobin Composition

Embryonic Hemoglobin:Gower 1 �2-�2Gower 2 �2-�2Portland �2-�2

Fetal Hemoglobin:F �2-�2

Adult Hemoglobin:A �2-�2A2 �2-�2

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that found in later life. Under stress, the older infant andadult increase production of Hgb F. Increased Hgb Fproduction often occurs in leukemic states and in otherconditions. (27)(28) The delay in the switch of Hgb F toHgb A has been noted in conditions of maternal hypoxia, ininfants who are small for gestational age, (29) and in infants

of diabetic mothers. (30)(31) Ele-vated concentrations of Hgb F mayhave protective effects in some dis-ease states. For example, a high con-centration of fetal Hgb F in patientswho have sickle cell disease may be apredictor of increased adult life ex-pectancy. (32)(33)

On a body weight basis, red bloodcell production during the lattermonths of gestation is significantlygreater compared with that in adultlife. Immediately after birth, erythro-poiesis is considerably reduced, asso-ciated with a steady and linear declinein �-chain synthesis during the pe-riod of reduced neonatal erythropoi-esis. Newly synthesized red blood cellsappearing in the circulation whenerythropoiesis resumes contain pre-dominantly Hgb A. The postpartumdecline of Hgb F production and of

the intercellular distribution of fetal and adult Hgb overthe first postnatal months has been extensively examined.Immediately after birth, there is a brief rise in Hgb F,followed by a steady decline. Studies of the intercellulardistribution of Hgb F (using an acid-elution technique)have shown that the distribution of Hgb F is heterogeneous

over the first few months after birth.At 3 months, the distribution ofHgb F becomes bimodal, with pop-ulations of cells that contain acid-resistant Hgb F and populations ofcells containing Hgb A. These obser-vations have suggested that HgbF-containing cells are replaced by apopulation of cells containing Hgb Aduring the early postnatal period.

Studies show that the type ofglobin chains produced at differentstages of development are not closelyrelated to the site of erythropoiesis.It appears that �- and �-chains aresynthesized in both primitive anddefinitive cell lines. Moreover, dur-ing the later stages of fetal develop-ment, the switch from �- to �-chainproduction occurs synchronouslythroughout the liver and bonemarrow. The transition from �- to�-chain synthesis is most closely re-

Figure 4. Production of globin chains during the fetal and neonatal period.

Figure 5. Hemoglobin production during the fetal and neonatal period.

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lated to postconceptional age and not chronologic age.(27) Thus, infants born preterm continue to synthesizesignificant amounts of �-globin (and fetal Hgb) until40 weeks’ gestation.

2,3-DPG MetabolismThe affinity of Hgb for oxygen can be decreased byinteraction with certain organic phosphates, such as2,3-DPG and adenosine triphosphate. (34) The highlycharged anion 2,3-DPG binds to deoxyhemoglobin butnot to oxyhemoglobin. Deoxyhemoglobin F does notpossess as great an affinity for 2,3-DPG as does deoxy-hemoglobin A and, therefore, cannot bind 2,3-DPG tothe same degree as Hgb A. Thus, the fetal leftward-shifted Hgb oxygen dissociation curve (Fig. 6) is noteasily modulated in the presence of 2,3-DPG.

The P50 (partial pressure of oxygen at which half ofHgb is saturated) of fetal blood is 19 to 21 mm Hg, some6 to 8 mm Hg lower than that of adult blood. As Hgb Fconcentration declines after birth, however, there is amarked rightward shift in the postnatal Hgb oxygenequilibrium curve. The percentage of Hgb A and the redcell 2,3-DPG content play the greatest roles in alteringthe position of the Hgb oxygen dissociation curve. As aresult, preterm infants who have a greater proportion ofHgb A but less 2,3-DPG (which occurs following packedred blood cell transfusion) may have a similar P50 as thosewho have increased quantities of Hgb F.

Certain factors are known to alter the affinity of Hgb foroxygen (Table 2). The most important of these are the HgbF concentration and the red cell 2,3-DPG content. Theconcentration of red blood cell 2,3-DPG gradually in-creases with gestation. At term, the concentration is similarto that of adults. By the end of the first postnatal week, the2,3-DPG concentrations are considerably higher than theyare at birth. After the first week, red blood cell 2,3-DPGconcentrations remain relatively unchanged for the next6 months. In term infants, the Hgb-oxygen dissociationcurve gradually shifts to the right, and by 4 to 6 months ofage, the P50 values approximate those of the adult.

The situation is somewhat different in preterm in-fants. Because Hgb F synthesis is still active, increases inP50 seen in term infants as a result of the switch fromHgb F to Hgb A do not occur as rapidly. The red bloodcell 2,3-DPG concentrations also are slightly lower inpreterm infants. (35) These concentrations are increasedwith the use of human recombinant Epo, which shifts theoxygen dissociation curve to the right. (36)(37)

Nitric Oxide-hemoglobin InteractionsNO plays a significant role in vasoactive regulation.Under baseline conditions, NO is produced by endo-thelial NO synthase and diffuses into surrounding smoothmuscle cells, activating soluble guanylyl cyclase to producecyclic guanosine 5�-monophosphate, and regulates vasculartone. NO reacts with oxyhemoglobin to form methemo-

globin, which is reversed by erythro-cytic methemoglobin reductase. Asecond reaction also can occur, inwhich NO reacts with deoxyhemo-globin to form nitrosyl hemoglobin(NO-Hgb). There is some evidencethat erythrocytes containing NO-Hgb may be able to release NO intothe circulation, thus causing vasodi-latation in the microvasculature. Athird reaction has been studied thatinvolves the binding of NO to the�-chain cysteine amino acid to formS-nitrosyl-hemoglobin (SNO-Hgb).It has been postulated that nitriteions within erythrocytes can be re-duced to NO by deoxyhemoglobin,so NO is generated as erythrocytesenter hypoxic regions. All of thesepotential mechanisms result in NOcontrolling blood flow via hypoxicvasodilatation. These mechanismsare especially important in preterm

Figure 6. Hemoglobin-oxygen dissociation curve. The curve representing fetal hemoglo-bin is on the left, and the curve representing adult hemoglobin is on the right. The P50 isshown as a hatched line for each curve.

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infants because vulnerable vascular beds such as the splanch-nic system are at risk for hypoxic injury via shunting ofblood to the brain and heart. Blood that is collected fortransfusion loses its SNO-Hgb within hours, so transfusedpacked red blood cells (PRBCs) lack NO. TransfusingPRBCs that cannot deliver NO to the microvasculaturemay, in fact, reduce local oxygen delivery to tissues throughvasoconstriction. Studies are in progress to evaluate therenitrosylization of Hgb before transfusion.

Oxygen TransportThe mechanisms controlling oxygen transport in uteroand immediately postpartum are complex. During pre-natal life, the fetal arterial oxygen tension (PO2) is ap-proximately 30 mm Hg, and the venous PO2 is approxi-mately 15 mm Hg (Fig. 6). These low PO2s contribute tothe development of relative polycythemia in the fetus.After birth, numerous factors affect oxygenation, includ-ing the inspired gas mixture, pulmonary function, thearterial oxygen dissociation curve, and the ability toextract oxygen at the tissue level. (38) It has been spec-ulated that the actual amount of oxygen released to

tissues may be greater in utero because of the character-istics of the Hgb-oxygen dissociation curve.

If pulmonary function is normal, the PO2 of pulmo-nary blood rises from the 40 mm Hg of pulmonaryarterial blood to the 100 mm Hg of pulmonary venousblood. Because of the shape of the Hgb-oxygen dissoci-ation curve, these PO2 values permit 95% saturation ofHgb by oxygen. Further increases in PO2 produce littleadditional increase in saturation. In the healthy adult,approximately 50% of Hgb is saturated with oxygenwhen the PO2 falls to 27 mm Hg (P50�27 mm Hg). Insituations in which the Hgb-oxygen dissociation curvehas shifted to the right, the affinity of Hgb for oxygen isreduced. Thus, at any given PO2, more oxygen is releasedto tissues. Conversely, if the curve is shifted to the left,the affinity of Hgb for oxygen is increased. Therefore, atany given PO2, less oxygen is released to the tissues.

A precise relationship does not exist between the declinein Hgb F and the decrease in oxygen affinity of a neonate’sblood. (38) Rather, changes in P50 reflect the interactionbetween red blood cell 2,3-DPG, the increase in Hgb Athat occurs after birth, and the decline in Hgb F. Althoughoxygen-carrying capacity (Hgb concentration � oxygensaturation � 1.36 mL oxygen/g of Hgb) decreases overthe first few postnatal months as Hgb concentration de-clines, the amount of oxygen delivery can remain similar oreven increase. (35) For example, a preterm infant born witha Hgb concentration of 15 g/dL (150 g/L) delivers 1 mLof oxygen to the tissues for every 100 mL of circulatingblood (based on a P50 of 19 and a central venous PO2 of40 mm Hg). As the percent of Hgb A increases over time,the P50 shifts to the right. The infant can now deliver2.1 mL of oxygen per 100 mL of blood, despite a decreasein total Hgb to 8 g/dL (80 g/L) (based on a P50 of 24 mmHg and a central venous PO2 of 40 mm Hg). (35)

After intrauterine transfusion, infants have oxygen-unloading properties characteristic of adult blood. Despitethe decrease in oxygen affinity that accompanies intrauter-ine transfusion, no deleterious effects of this procedure withrespect to oxygen uptake by the fetus have been docu-mented. (39) The physiologic significance of manipulatingthe Hgb-oxygen affinity of extremely preterm infants viaPRBC transfusions continues to be studied. It is importantto understand an infant’s ability to deliver oxygen to tissueswhen determining whether to administer an erythrocytetransfusion. The decision to transfuse should not be basedon Hgb concentration alone. Transfusions significantly af-fect an infant’s endogenous erythropoiesis: for infants whoundergo exchange transfusion or multiple transfusions,both Epo concentrations and reticulocyte counts are lowerat any given Hgb concentration. (8)(40) The search con-

Table 2. Factors AffectingHemoglobin-Oxygen AffinityIncreased P50, increased red blood cell 2,3-DPG:

● Adaptation to high altitude● Hypoxemia associated with chronic pulmonary disease● Hypoxemia associated with cyanotic heart disease● Anemia● Decreased red blood cell mass● Hyperthyroidism● Red cell pyruvate kinase deficiency

Increased P50, no consistent alteration in red blood cellDPG:

● Abnormal hemoglobins (Kansas, Seattle,Hammersmith, Tacoma, E)

● Vigorous exercise

Decreased P50, decreased red blood cell 2,3-DPG:

● Septic shock● Severe acidosis● Following massive transfusions of stored blood● Neonatal respiratory distress syndrome

Decreased P50, no consistent alteration in red blood cellDPG:

● Abnormal hemoglobins (Kempsey, Chesapeake,Capetown, Yakima, Rainier)

2,3-DPG�2,3 diphosphoglycerate, P50�partial pressure of oxygen atwhich half of hemoglobin is saturated

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tinues for a specific marker that reflects the need for im-proved oxygen delivery to tissues (via red blood cell trans-fusion). Currently, no ideal marker that is simple, requireslittle or no blood, is reproducible, and can be applied topreterm infants exists for clinical use in neonates.

SummaryThe organized transition from embryonic to fetal to adultHgb has been extensively studied, providing significantunderstanding of the molecular basis of Hgb development.Studies continue to evaluate the relationship between Hgbconcentrations and oxygen delivery in neonates to bestdetermine what Hgb concentrations best meet the needs ofa wide variety of clinical situations from the critically illextremely low-birthweight infant to the stable growingpreterm infant. Studies are underway to explore the mech-anisms linking Hgb metabolism and the transfer of NO byerythrocytes, and these studies have the potential to addgreatly to the body of evidence regarding transfusion guide-lines in various neonatal populations.

ACKNOWLEDGMENTS. I wish to thank Rebecca Mo-ran, MD, and Andrea Duncan, MD, for their thoughtfulreview and comments and Ann Chavez for her assistancein completing the manuscript.

References1. Forestier F, Daffos F, Catherine N, Renard M, Andreux JP.Developmental hematopoiesis in normal human fetal blood. Blood.1991;77:23602. Bratteby L. Studies on the erythro-kinetics in infancy: red cellvolume of newborn infants in relation to gestational age. ActaPaediatr Scand. 1968;57:1323. Jopling J, Henry E, Wiedmeier SE, Christensen RD. Referenceranges for hematocrit and blood hemoglobin concentration duringthe neonatal period: data from a multihospital health care system.Pediatrics. 2009;123:e333–e3374. Alur P, Devapatla SS, Super DM, et al. Impact of race andgestational age on red blood cell indices in very low birth weightinfants. Pediatrics. 2000;106:306–3105. Usher R, Shephard M, Lind J. The blood volume of a newborninfant and placental transfusion. Acta Paediatr Scand. 1963;52:4976. Oski FA. The erythrocyte and its disorders. In: Oski FA, Nathan

DG, eds. Hematology of Infancy and Childhood. Philadelphia, PA:WB Saunders; 1993:18–437. Kling PJ, Schmidt RL, Roberts RA, Widness JA. Serum eryth-ropoietin levels during infancy: associations with erythropoiesis.J Pediatr. 1996;128:7918. Stockman JA 3rd, Garcia JF, Oski FA. The anemia of prematu-rity: factors governing the erythropoietin response. N Engl J Med.1977;296:6479. Humbert JR, Abelson H, Hathaway WE, Battaglia FC. Poly-cythemia in small for gestational age infants. J Pediatr. 1969;75:81210. Hakanson DO, Oh W. Hyperviscosity in the small for gesta-tional age infant. Pediatr Res. 1977;11:472A11. Moore LG, Newberry MA, Freeby GM, Crnic LS. Increasedincidence of neonatal hyperbilirubinemia at 3100 m in Colorado.Am J Dis Child. 1984;138:15812. Bureau MA, Shapcott D, Berthiaumey, et al. Maternal ciga-rette smoking and fetal oxygen transport: a study of P50, 2,3-diphosphoglycerate, total hemoglobin, hematocrit, and type F he-moglobin in fetal blood. Pediatrics. 1983;2:2213. Matoth Y, Zaizove R, Varsano I. Postnatal changes in some redcell parameters. Acta Paediatr Scand. 1971;60:31714. Gonzales GF, Steenland K, Tapia V. Maternal hemoglobinlevel and fetal outcome at low and high altitudes. Am J Physiol RegulIntegr Comp Physiol. 2009;297:R1477–R148515. Nelson SM, Freeman DJ, Sattar N, Lindsay RS. Erythrocytosisin offspring of mothers with type 1 diabetes—are factors other thaninsulin critical determinants? Diabet Med. 2009;26:887–89216. Weatherall DJ, Wood WG, Jones RW, Clegg JB. The develop-mental genetics of human hemoglobin. In: Stamatoyannopoulos G,Nienhuis AW, eds. Experimental Approaches for the Study of Hemo-globin Switching. New York, NY: Alan R Liss; 1985:3–2517. Papayannopoulou T, Kurachi S, Brice M, Nakamoto B, Stama-toyannopoulos G. Asynchronous synthesis of HbF and HbA duringerythroblast maturation. II. Studies of G gamma, A gamma, andbeta chain synthesis in individual erythroid clones from neonataland adult BFU-E cultures. Blood. 1981;57:53118. Kleihauer E. The hemoglobins. In: Stave U, ed. Physiology of thePerinatal Period. Vol 1. New York, NY: Appleton-Century-Crofts;1970:25519. Masala B, Manca L, Formato M, Pilo G. A study of the switchof fetal hemoglobin and newborn erythrocytes fractionated bydensity gradient. Hemoglobin. 1983;7:56720. Schroeder WA, Shelton JR, Shelton JB, Apell G, Huisman TH,Bouver NG. Worldwide occurrence of nonallelic genes for the gamma-chain of human foetal haemoglobin in newborns. Nature. 1972;240:27321. Schroeder WA, Huisman THJ, Brown AK, et al. Postnatalchanges in chemical heterogeneity of human fetal hemoglobin.Pediatr Res. 1971;5:47322. Schroeder WA, Huisman THJ. Human gamma-chains: struc-tural features. In: Stamatoyannopoulos G, Nienhuis AW, eds. Cel-lular and Molecular Regulation of Hemoglobin Switching. NewYork, NY: Grune & Stratton; 1979:29–4523. Szelengi JG, Holland SR. Studies on the structure of humanembryonic hemoglobin. Acta Biochim Biophys Acad Sci Hung. 1969;4:4724. Hecht F, Motulsky AG, Lemire RJ, Shepard TE. Predomi-nance of hemoglobin Gower 1 in early human embryonic develop-ment. Science. 1966;152:9125. Heizman THJ, Schroeder WA, Brown AK, Hyman CB, Or-tega JA, Sukumaran PK. Further studies of the postnatal change inchemical heterogeneity of human fetal hemoglobin in several ab-normal conditions. Pediatr Res. 1975;9:1

American Board of Pediatrics Neonatal-PerinatalMedicine Content Specifications• Know the biochemical characteristics of

fetal hemoglobin.• Know the developmental biology of

hemoglobin types.• Know normal erythropoiesis in the fetus

and neonate.

core concepts hemoglobin

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26. Kleihauer E, Braun H, Betke K. Demonstration of fetal hemoglo-bin in the erythrocytes of a blood smear. Klin Wochenschr. 1957;35:63727. Bard H, Lachance C, Widness JA, Gagnon C. The reactivationof fetal hemoglobin synthesis during anemia of prematurity. PediarRes. 1994;36:25328. Bard H, Fouron JC, Gagnon C, Gagnon J. Hypoxemia andincreased fetal hemoglobin synthesis. J Pediatr. 1994;124:94129. Bard H. The effect of placental insufficiency on fetal hemoglobinand adult hemoglobin synthesis. Am J Obstet Gynecol. 1974;120:6730. Bard H, Prosmanne J. Relative rates of fetal hemoglobin andadult hemoglobin synthesis in the cord blood of infants of insulin-dependent diabetic mothers. Pediatrics. 1985;75:114331. Perrine SP, Greene MF, Faller DV. Delay in fetal hemoglobinswitch in infants of diabetic mothers. N Engl J Med. 1985;312:33432. Platt OS, Brambilla DJ, Rosse WF, et al. Mortality in sickle celldisease. Life expectancy and risk factors for early death. N EnglJ Med. 1994;330:163933. Trompeter S, Roberts I. Haemoglobin F modulation in child-hood sickle cell disease. Br J Haematol. 2009;144:308–31634. Benesch R, Benesch RE, Yu CL. Reciprocal binding of oxygen

and diphosphoglycerate by human hemoglobin. Proc Natl Acad SciU S A. 1968;59:52635. Delivoria-Papadopoulos M, Roncevic NP, Oski FA. Postnatalchanges in oxygen transport of term, preterm and sick infants: the roleof red cell 2,3 diphosphoglycerate in adult hemoglobin. Pediatr Res.1971;5:23536. Soubasi V, Kremenopoulos G, Tsantal C, Savopoulou P, Mus-safiris C, Dimitriou M. Use of erythropoietin and its effects on bloodlactate and 2, 3-diphosphoglycerate in premature neonates. Biol Neo-nate. 2000;78:28137. Debska-Slizien A, Owczarzak A, Lysiak-Szydlowska W, RutkowskiB. Erythrocyte metabolism during renal anemia treatment with recombi-nant human erythropoietin. Int J Artif Organs. 2004;27:935–94238. Stockman JA. Anemia of prematurity: current concepts in theissue of when to transfuse. Pediatr Clin North Am. 1986;33:11139. Novy MJ, Frigoletto FD, Easterday CL, Umansky I, Nelson NM.Changes in umbilical-cord blood oxygen affinity after intrauterinetransfusions for erythroblastosis. N Engl J Med. 1971;285:58940. Oski FA, Stockman JA. Anaemia in early infancy. Br J Haema-tol. 1974;27:195

core concepts hemoglobin

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NeoReviews Quiz

9. Red blood cell production decreases after birth, primarily as a result of increased availability of oxygen,which greatly reduces erythropoietin production and endogenous erythropoiesis. A decrease in hemoglobinconcentration follows this reduced red blood cell production. Of the following, the hemoglobin nadir inhealthy term infants is reached at a postnatal age closest to:

A. 8 weeks.B. 12 weeks.C. 16 weeks.D. 20 weeks.E. 24 weeks.

10. Hemoglobin consists of heme, an iron-containing protoporphyrin, and globin, a polypeptide. Eight globingenes direct the synthesis of six different polypeptide chains, designated as alpha (�), beta (�), gamma(�), delta (�), epsilon (�), and zeta (�). These globin chains combine in the developing erythroblast toform seven different hemoglobin tetramers: Gower 1 (�2-�2), Gower 2 (�2-�2), Portland (�2-�2), fetalhemoglobin (Hgb F: �2-�2), adult hemoglobin (Hgb A: �2-�2), and adult hemoglobin A2 (Hgb A2: �2-�2).Of the following, the most prevalent hemoglobin tetramer in the fetus at 18 weeks of gestational age is:

A. Gower 1.B. Hgb A.C. Hgb A2.D. Hgb F.E. Portland.

11. A term infant is born with severe anemia. A Kleihauer Betke test is performed on maternal blood todetermine whether fetomaternal hemorrhage is the cause. Of the following, the property of fetalhemoglobin that best differentiates fetal from maternal red blood cells using the Kleihauer Betke test isthat the fetal hemoglobin, relative to adult hemoglobin, is/has:

A. Decreased interaction with 2,3-diphosphoglycerate.B. Greater affinity for oxygen.C. Greater solubility in strong phosphate buffer.D. Readily oxidized to methemoglobin.E. Resistant to acid elution.

core concepts hemoglobin

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DOI: 10.1542/neo.12-1-e29 2011;12;e29-e38 NeoReviews

Robin K. Ohls Core Concepts: The Biology of Hemoglobin

 

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