February 1975
194
The Journal o f P E D I A T R I C S
Iron-deficiency anemia: Evaluation of compensatory changes Compensatory mechanisms in children with iron-deficiency anemia were evaluated by measuring erythmeytic organic phasphates and, in some cases, shifts in the Pso of the oxygen dissociation curve. In 19 children with nutritional anemia (hemoglobin values o f 3.2 to 8.2 gm/dl) there was a calculated improved oxygen delivery to tissues equivalent to a hemoglobin level o f at least 7.5 gm/dl. Transient decompensation was observed during acidosis. In ,five children with iron-deficiency anemia due to blood loss and in one child with rheumatoid arthritis no such compensatory changes were observed.
V. Albert Lovric, M.B., B.S.(Syd.), D.C.P., M.R.A.C.P., F.R.C.P.A., M.R.C. P a t h . , * P a t r i d a J . B e a l , M . S e . , a n d A h t i T. L a m m i ,
M.B., B.S. (Syd.), F.R.A.C.P., F.R.C.P.A.,
Sydney Australia
IRON-DEFICIENCY
ANEMIA
is a frequently e n c o u n -
t e r e d and usually unsuspected pediatric disease. This is
probably related to compensatory mechanisms during the progression of the anemia) With low hemoglobin values, urgent correction with parenteral iron or blood transfusion may be considered. Clinical findings rarely give cause for concern. A complicating feature may be intercurrent illness. The main consequence of anemia is decrease in the capacity for oxygen delivery to tissues. The usual clinical signs of compensation during progression of anemia are the increases in cardiac output and rate. It has recently become recognized that in response to anemia, the oxygen dissociation curve may become shifted to the right. This implies that at any given partial pressure more oxygen will be delivered to tissues. The measurem e n t of the oxygen dissociation curve is presently not practicable in most laboratories. Determination of the Ps0value allows for approximate assessment of such improved tissue oxygenation. The P50 value is defined as partial pressure of oxygen at which 50% saturation of hemoglobin is present, corrected to pH 7.4 and 37~
One of the factors which alters the position of the oxygen d i s s o c i a t i o n c u r v e is the level o f e r y t h r o c y t e organic p h o s p h a t e s , which i n c r e a s e s with anemia. These compounds are known to stabilize hemoglobin in the deoxygenated state. Consequently, a right shift in the oxygen dissociation curve will be induced, with improved oxygen delivery to tissues, Acidosis also shifts the oxygen dissociation curve to the right. However, during acidosis, g e n e r a t i o n of e r y t h r o c y t e organic phosphates is usually reduced. Unless this complication is present, the measurement of red blood cell organic phosphate provides an indication of the extent of compensation for anemia, when Ps0cannot be determined. Abbreviations used 2,3-DPG: 2,3-diphosphoglycerate ATP: adenosine triphosphate The purpose of this report is to confirm and discuss significance of both right-shifted Ps0 values and elev a t e d levels of e r y t h r o c y t e organic p h o s p h a t e s in children with iron-deficiency anemia.
MATERIAL A N D M E T H O D S From the Department of Hematology, Royal A lexandra Hospital for Children. *Reprintaddress':Departmentof Hematology, Royal A lexandra Hospitalfor Children,BridgeR d., Camperdown,N.S. W., Australia.
Vol, 86, No. Z pp. 194-197
As part of the investigation in children aged 6 months to 3 years with iron-deficiency anemia and hemoglobin levels b e l o w 8.5 g m / d l , s o m e e r y t h r o c y t i c organic phosphates were measured (Table I). Older children
Volume 86 Number 2
Iron-deficiency anemia
195
Table I. Children aged 6 to 36 m o n t h s with nutritional iron deficiency a n e m i a
Case No.
Age (too)
Hemoglobin (gm/dl) 4.5 5.4 7.1 6.5 7.0 8.0 5.1 4,2 8.2 5.2 7.7 4.2 7.9 7.9 3.9 5.5 3.7 5.9 12.6 7.8 3.2 3.2 6.0 • 1.73
1
11
2 3 4 5 6 7 8 9 10 11 12 13
22 18 14 15 18 18 9 23 13 15 10 6
14 15 16 17
i2 12 24 8
18 19
10 5
Mean • 1SD Range in normal children • 1SD
2,3-DPG (tzm/gm hemoglobin) 25.1 29.2 36.0 23.1 26.0 24.8 25.5 33.1 27,8 23.1 29.5 37.0 13.9 23.4 37.2 32.7 32.0 23.6 26.9 28.7 23.9 27.35 • 5.47 16.45 • 3.41
A TP (txm/gm hemoglobin)
P5o
(ram Hg)
Comment
2.9 3.5 2.4 4.3
4.2 1.3 2.2
With acidosis Corrected acidosis
4.1 5.1
41.0 45.7 49.3 29.6 34.0 52.0 43.0 41.9 + 8.8 33.1 -+ 12
5.5 3.8 • 1.1 3.2 • 1.1
Before blood transfusion After blood transfusion
With acidosis
Table II. Children with iron deficiency a n e m i a related to blood loss or r h e u m a t o i d arthritis
Case No.
, Age (yr)
1 2 3 4 5 6
1 10 4 8 6 12
Diagnosis Chronic intestinal blood loss Rheumatoid arthritis Chronic intestinal blood loss Acute intestinal blood loss Chronic intestinal blood loss Chronic intestinal blood loss
Hemoglobin (gm/dl)
% Saturation of transferrin
8.6 8.8 5.2 8.4 4.5 4.3
13 2 6 18 8 5
Range in normal children • 1 SD
with anemia, usually the result of blood loss, were also investigated ( T a b l e II). H e m a t o l o g i c investigations were p e r f o r m e d according to standard techniques. 2,3-Diphosphoglycerate was e s t i m a t e d u s i n g C a l b i o c h e m test kits ( m e t h o d o f N y g a a r d and R~rth2). A d e n o s i n e triphosphate levels were assayed by the method of B~cher, 3 using B o e h r i n g e r test kits. Ps0 m e a s u r e m e n t s w e r e d e t e r -
mined according Strumia. 4
2,3-DPG (Ixm/gmhemoglobin)
(mm Hg)
12.4 19.0 16.9 9.4 15.5 25.2
42.6
15.0 • 2.0
31.1 • 2.2
to t h e m e t h o d
of Strumia
and
RESULTS Figs. 1 and 2 s h o w the values obtained for 2,3-DPG and, w h e r e d e t e r m i n e d , Ps0 respectively, c o m p a r e d to h e m o g l o b i n levels. W i t h two e x c e p t i o n s , s i g n i f i c a n t elevations inversely proportional to h e m o g l o b i n levels
196
Lovric et al.
The Journal of PediatricS February 1975
A ,c.o
_o
CHILDREN AGED
O
6--36
MONTHS
Controls 9 Iron Deficiency Anaemia 9 Iron Deficiency A n a e m i a Changes w i t h Acidosis
o Normal
E
I"
---=40E
@9
LU
o
~ a.
i
3
5
7 HAEMOGLOBIN
9
11
13
15
(g/1OOml)
Fig. 1. Relationship of erythrocyte 2,3-DPG concentration to hemoglobin level in iron-deficient children aged 6 to 36 months. CHILDREN
AGED
.r-
i i:
50e-
.2 "6 o
,~ o
40-
DISCUSSION
MONTHS
NORMAL CONTROLS 9 IRON DEFICIENCY ANAEMIA [~ IRON DEFICIENCY ANAEMIA CHANGES WITH ACIDOSIS
E
E
6--36
i
c
o
~ 8
8
g 30 0 a..
202
6
8
HAEMOGLOBIN
1'0
12
la,
16
(g//1OOml)
Fig. 2. Relationship of Ps0 value to hemoglobin level in irondeficient children aged 6 to 36 months. were observed in all patients with nutritional iron-deficiency anemia (Table I). ATP levels were also determined in some cases, but showed no distinct elevation above normal levels. Data on patients with iron-deficiency anemia complicated with other disorders are presented in Table II. W h e r e acute blood loss was superimposed, the 2,3-DPG levels were not elevated.
The elevated 2,3-DPG values and right-shifted Ps0 values found in iron-deficient children indicate compensation for anemia. Similar compensation has been reported for other types of anemia, and the numerical relationship between Ps0 and 2,3-DPG values has been investigated. 5-7 Insufficient determinations have been carried out in this work for precise definition of this relationship. Children with slowly evolving iron-deficiency anemia ( T a b l e I) have b e e n s h o w n to have c o m p e n s a t o r y mechanisms in their erythrocytes. F r o m information given by Oski I and calculations regarding right-shift changes in the Ps0value (Table I) in anemia, a guide to the degree of compensation may be given. For instance, with a hemoglobin level of 7.0 gm/dl and a Ps0 value right shifted by 10 mmHg, oxygen delivery to tissues would be approximately equivalent to that with a hemoglobin level of 12.0 gm/dl. Thus patients listed in Table I (with one exception) would have had oxygen unloading potential equivalent to hemoglobin levels of at least 7.5 gm/dl. This is in keeping with the observation that iron-deficiency anemia in children is usually asymptomatic and clinically not detectable unless complicated by intercurrent illness. Urgent correction of anemia is thus not essential. In children with more acute anemia, such as acute blood loss (Table II), initial compensation may n o t be a d e q u a t e and a n e m i a m a y readily b e c o m e symptomatic.
Volume 86 Number 2
The two exceptions (with low 2,3-DPG levels in Table I) warrant further mention. Case 13 was admitted twice previously to another hospital for diarrhea during the preceeding three weeks. On each admission he was dehydrated and in metabolic acidosis. W h e n transferred to this hospital he was again dehydrated and had clinical and laboratory evidence of metabolic acidosis. At that time the 2,3-DPG level was within normal limits. Within 24 hours (after r e h y d r a t i o n and correction of acidosis) the 2 , 3 - D P G level rose significantly. T h e other, an asymptomatic child (Case 19 in Table I), was being investigated for uncomplicated iron-deficiency anemia, at which time both the 2,3-DPG and Ps0 levels indicated significant compensatory changes. While in the hospital he contracted infectious diarrhea and suddenly became ill and dehydrated commensurate with the marked decrease in both 2,3-DPG and Ps0 values. In practice, we do not recommend blood transfusions or parenteral iron therapy as treatment for pediatric iron-deficiency anemia. Blood stored for transfusion for longer than one week may have increased affinity for oxygen, as erythrocytic organic phosphates decrease on storage, resulting in a left-shifted oxygen dissociation curve. W h e n such blood is transfused, it may take six hours or more before regeneration of organic phosphates occurs. Such blood will certainly improve hemoglobin level and the color of an anemic patient, b u t tissue anoxia may not be corrected as the transfused blood has an increased oxygen affinity for some hours. Case 17 (Table I) illustrates this point. Significant compensatory changes were recorded initially, but immediately following blood transfusion with packed erythrocytes the Ps0 value fell.
Iron-deficiency anemia
197
P a r e n t e r a l iron therapy confers no a d v a n t a g e in speed of response when compared to oral medications. This study failed to demonstrate a rise in A T P levels in iron-deficiency anemia in children between the ages of 6 months and 3 years, in contrast to the observation recorded by Card a n d Brain. 8 More i n f o r m a t i o n is needed on this subject. We would like to thank Professor T. Stapleton for the use of the Radiometer equipment on which the Ps0 measurements were made. REFERENCES
1. Oski FA: Designation of anemia on a functional basis, J PED1ATR83:353, 1973. 2. Nyggaard SF, and R~rth M: An enzymatic assay of 2,3diphosphoglycerate in blood, Stand J Clin Lab Invest 24:399, 1969. 3. B~,cher T: Uber ein phosphatubertragendes G~irungsferment, Biochim Biophys Acta 1:292, 1947. 4. Strumia PV, and Strumia MM: A rapid micro Ps0 determination method to ascertain the position of the oxygen dissociation curve of whole blood, Am J Clin Pathol 59:731, 1973. 5. Duc G, and Engel K: Effect of 2,3-DPG concentration on hemoglobin-oXygen affinity of whole blood, Scand J Clin Lab Invest 24:405, 1969. 6. Oski FA, Gottlieb AJ, Miller WW, and DelivoriaPapadopoulos M: The effects of deoxygenation of adult and fetal hemoglobin on the synthesis of red cell 2,3diphosphoglycerate and its in vivo consequences, J Clin Invest 49:400, 1970 7. Torrance J, Jacobs P, Restrepo A, Eschbach J, Lenfant C, and Finch CA: Intraerythrocytic adaptation to anemia, N Engl J Med 283:165, 1970. 8. Card RT, and Brain MC: The "anemia" of childhood, N Engl J Med 288:388, 1973.
194
The Journal o f P E D I A T R I C S
Iron-deficiency anemia: Evaluation of compensatory changes Compensatory mechanisms in children with iron-deficiency anemia were evaluated by measuring erythmeytic organic phasphates and, in some cases, shifts in the Pso of the oxygen dissociation curve. In 19 children with nutritional anemia (hemoglobin values o f 3.2 to 8.2 gm/dl) there was a calculated improved oxygen delivery to tissues equivalent to a hemoglobin level o f at least 7.5 gm/dl. Transient decompensation was observed during acidosis. In ,five children with iron-deficiency anemia due to blood loss and in one child with rheumatoid arthritis no such compensatory changes were observed.
V. Albert Lovric, M.B., B.S.(Syd.), D.C.P., M.R.A.C.P., F.R.C.P.A., M.R.C. P a t h . , * P a t r i d a J . B e a l , M . S e . , a n d A h t i T. L a m m i ,
M.B., B.S. (Syd.), F.R.A.C.P., F.R.C.P.A.,
Sydney Australia
IRON-DEFICIENCY
ANEMIA
is a frequently e n c o u n -
t e r e d and usually unsuspected pediatric disease. This is
probably related to compensatory mechanisms during the progression of the anemia) With low hemoglobin values, urgent correction with parenteral iron or blood transfusion may be considered. Clinical findings rarely give cause for concern. A complicating feature may be intercurrent illness. The main consequence of anemia is decrease in the capacity for oxygen delivery to tissues. The usual clinical signs of compensation during progression of anemia are the increases in cardiac output and rate. It has recently become recognized that in response to anemia, the oxygen dissociation curve may become shifted to the right. This implies that at any given partial pressure more oxygen will be delivered to tissues. The measurem e n t of the oxygen dissociation curve is presently not practicable in most laboratories. Determination of the Ps0value allows for approximate assessment of such improved tissue oxygenation. The P50 value is defined as partial pressure of oxygen at which 50% saturation of hemoglobin is present, corrected to pH 7.4 and 37~
One of the factors which alters the position of the oxygen d i s s o c i a t i o n c u r v e is the level o f e r y t h r o c y t e organic p h o s p h a t e s , which i n c r e a s e s with anemia. These compounds are known to stabilize hemoglobin in the deoxygenated state. Consequently, a right shift in the oxygen dissociation curve will be induced, with improved oxygen delivery to tissues, Acidosis also shifts the oxygen dissociation curve to the right. However, during acidosis, g e n e r a t i o n of e r y t h r o c y t e organic phosphates is usually reduced. Unless this complication is present, the measurement of red blood cell organic phosphate provides an indication of the extent of compensation for anemia, when Ps0cannot be determined. Abbreviations used 2,3-DPG: 2,3-diphosphoglycerate ATP: adenosine triphosphate The purpose of this report is to confirm and discuss significance of both right-shifted Ps0 values and elev a t e d levels of e r y t h r o c y t e organic p h o s p h a t e s in children with iron-deficiency anemia.
MATERIAL A N D M E T H O D S From the Department of Hematology, Royal A lexandra Hospital for Children. *Reprintaddress':Departmentof Hematology, Royal A lexandra Hospitalfor Children,BridgeR d., Camperdown,N.S. W., Australia.
Vol, 86, No. Z pp. 194-197
As part of the investigation in children aged 6 months to 3 years with iron-deficiency anemia and hemoglobin levels b e l o w 8.5 g m / d l , s o m e e r y t h r o c y t i c organic phosphates were measured (Table I). Older children
Volume 86 Number 2
Iron-deficiency anemia
195
Table I. Children aged 6 to 36 m o n t h s with nutritional iron deficiency a n e m i a
Case No.
Age (too)
Hemoglobin (gm/dl) 4.5 5.4 7.1 6.5 7.0 8.0 5.1 4,2 8.2 5.2 7.7 4.2 7.9 7.9 3.9 5.5 3.7 5.9 12.6 7.8 3.2 3.2 6.0 • 1.73
1
11
2 3 4 5 6 7 8 9 10 11 12 13
22 18 14 15 18 18 9 23 13 15 10 6
14 15 16 17
i2 12 24 8
18 19
10 5
Mean • 1SD Range in normal children • 1SD
2,3-DPG (tzm/gm hemoglobin) 25.1 29.2 36.0 23.1 26.0 24.8 25.5 33.1 27,8 23.1 29.5 37.0 13.9 23.4 37.2 32.7 32.0 23.6 26.9 28.7 23.9 27.35 • 5.47 16.45 • 3.41
A TP (txm/gm hemoglobin)
P5o
(ram Hg)
Comment
2.9 3.5 2.4 4.3
4.2 1.3 2.2
With acidosis Corrected acidosis
4.1 5.1
41.0 45.7 49.3 29.6 34.0 52.0 43.0 41.9 + 8.8 33.1 -+ 12
5.5 3.8 • 1.1 3.2 • 1.1
Before blood transfusion After blood transfusion
With acidosis
Table II. Children with iron deficiency a n e m i a related to blood loss or r h e u m a t o i d arthritis
Case No.
, Age (yr)
1 2 3 4 5 6
1 10 4 8 6 12
Diagnosis Chronic intestinal blood loss Rheumatoid arthritis Chronic intestinal blood loss Acute intestinal blood loss Chronic intestinal blood loss Chronic intestinal blood loss
Hemoglobin (gm/dl)
% Saturation of transferrin
8.6 8.8 5.2 8.4 4.5 4.3
13 2 6 18 8 5
Range in normal children • 1 SD
with anemia, usually the result of blood loss, were also investigated ( T a b l e II). H e m a t o l o g i c investigations were p e r f o r m e d according to standard techniques. 2,3-Diphosphoglycerate was e s t i m a t e d u s i n g C a l b i o c h e m test kits ( m e t h o d o f N y g a a r d and R~rth2). A d e n o s i n e triphosphate levels were assayed by the method of B~cher, 3 using B o e h r i n g e r test kits. Ps0 m e a s u r e m e n t s w e r e d e t e r -
mined according Strumia. 4
2,3-DPG (Ixm/gmhemoglobin)
(mm Hg)
12.4 19.0 16.9 9.4 15.5 25.2
42.6
15.0 • 2.0
31.1 • 2.2
to t h e m e t h o d
of Strumia
and
RESULTS Figs. 1 and 2 s h o w the values obtained for 2,3-DPG and, w h e r e d e t e r m i n e d , Ps0 respectively, c o m p a r e d to h e m o g l o b i n levels. W i t h two e x c e p t i o n s , s i g n i f i c a n t elevations inversely proportional to h e m o g l o b i n levels
196
Lovric et al.
The Journal of PediatricS February 1975
A ,c.o
_o
CHILDREN AGED
O
6--36
MONTHS
Controls 9 Iron Deficiency Anaemia 9 Iron Deficiency A n a e m i a Changes w i t h Acidosis
o Normal
E
I"
---=40E
@9
LU
o
~ a.
i
3
5
7 HAEMOGLOBIN
9
11
13
15
(g/1OOml)
Fig. 1. Relationship of erythrocyte 2,3-DPG concentration to hemoglobin level in iron-deficient children aged 6 to 36 months. CHILDREN
AGED
.r-
i i:
50e-
.2 "6 o
,~ o
40-
DISCUSSION
MONTHS
NORMAL CONTROLS 9 IRON DEFICIENCY ANAEMIA [~ IRON DEFICIENCY ANAEMIA CHANGES WITH ACIDOSIS
E
E
6--36
i
c
o
~ 8
8
g 30 0 a..
202
6
8
HAEMOGLOBIN
1'0
12
la,
16
(g//1OOml)
Fig. 2. Relationship of Ps0 value to hemoglobin level in irondeficient children aged 6 to 36 months. were observed in all patients with nutritional iron-deficiency anemia (Table I). ATP levels were also determined in some cases, but showed no distinct elevation above normal levels. Data on patients with iron-deficiency anemia complicated with other disorders are presented in Table II. W h e r e acute blood loss was superimposed, the 2,3-DPG levels were not elevated.
The elevated 2,3-DPG values and right-shifted Ps0 values found in iron-deficient children indicate compensation for anemia. Similar compensation has been reported for other types of anemia, and the numerical relationship between Ps0 and 2,3-DPG values has been investigated. 5-7 Insufficient determinations have been carried out in this work for precise definition of this relationship. Children with slowly evolving iron-deficiency anemia ( T a b l e I) have b e e n s h o w n to have c o m p e n s a t o r y mechanisms in their erythrocytes. F r o m information given by Oski I and calculations regarding right-shift changes in the Ps0value (Table I) in anemia, a guide to the degree of compensation may be given. For instance, with a hemoglobin level of 7.0 gm/dl and a Ps0 value right shifted by 10 mmHg, oxygen delivery to tissues would be approximately equivalent to that with a hemoglobin level of 12.0 gm/dl. Thus patients listed in Table I (with one exception) would have had oxygen unloading potential equivalent to hemoglobin levels of at least 7.5 gm/dl. This is in keeping with the observation that iron-deficiency anemia in children is usually asymptomatic and clinically not detectable unless complicated by intercurrent illness. Urgent correction of anemia is thus not essential. In children with more acute anemia, such as acute blood loss (Table II), initial compensation may n o t be a d e q u a t e and a n e m i a m a y readily b e c o m e symptomatic.
Volume 86 Number 2
The two exceptions (with low 2,3-DPG levels in Table I) warrant further mention. Case 13 was admitted twice previously to another hospital for diarrhea during the preceeding three weeks. On each admission he was dehydrated and in metabolic acidosis. W h e n transferred to this hospital he was again dehydrated and had clinical and laboratory evidence of metabolic acidosis. At that time the 2,3-DPG level was within normal limits. Within 24 hours (after r e h y d r a t i o n and correction of acidosis) the 2 , 3 - D P G level rose significantly. T h e other, an asymptomatic child (Case 19 in Table I), was being investigated for uncomplicated iron-deficiency anemia, at which time both the 2,3-DPG and Ps0 levels indicated significant compensatory changes. While in the hospital he contracted infectious diarrhea and suddenly became ill and dehydrated commensurate with the marked decrease in both 2,3-DPG and Ps0 values. In practice, we do not recommend blood transfusions or parenteral iron therapy as treatment for pediatric iron-deficiency anemia. Blood stored for transfusion for longer than one week may have increased affinity for oxygen, as erythrocytic organic phosphates decrease on storage, resulting in a left-shifted oxygen dissociation curve. W h e n such blood is transfused, it may take six hours or more before regeneration of organic phosphates occurs. Such blood will certainly improve hemoglobin level and the color of an anemic patient, b u t tissue anoxia may not be corrected as the transfused blood has an increased oxygen affinity for some hours. Case 17 (Table I) illustrates this point. Significant compensatory changes were recorded initially, but immediately following blood transfusion with packed erythrocytes the Ps0 value fell.
Iron-deficiency anemia
197
P a r e n t e r a l iron therapy confers no a d v a n t a g e in speed of response when compared to oral medications. This study failed to demonstrate a rise in A T P levels in iron-deficiency anemia in children between the ages of 6 months and 3 years, in contrast to the observation recorded by Card a n d Brain. 8 More i n f o r m a t i o n is needed on this subject. We would like to thank Professor T. Stapleton for the use of the Radiometer equipment on which the Ps0 measurements were made. REFERENCES
1. Oski FA: Designation of anemia on a functional basis, J PED1ATR83:353, 1973. 2. Nyggaard SF, and R~rth M: An enzymatic assay of 2,3diphosphoglycerate in blood, Stand J Clin Lab Invest 24:399, 1969. 3. B~,cher T: Uber ein phosphatubertragendes G~irungsferment, Biochim Biophys Acta 1:292, 1947. 4. Strumia PV, and Strumia MM: A rapid micro Ps0 determination method to ascertain the position of the oxygen dissociation curve of whole blood, Am J Clin Pathol 59:731, 1973. 5. Duc G, and Engel K: Effect of 2,3-DPG concentration on hemoglobin-oXygen affinity of whole blood, Scand J Clin Lab Invest 24:405, 1969. 6. Oski FA, Gottlieb AJ, Miller WW, and DelivoriaPapadopoulos M: The effects of deoxygenation of adult and fetal hemoglobin on the synthesis of red cell 2,3diphosphoglycerate and its in vivo consequences, J Clin Invest 49:400, 1970 7. Torrance J, Jacobs P, Restrepo A, Eschbach J, Lenfant C, and Finch CA: Intraerythrocytic adaptation to anemia, N Engl J Med 283:165, 1970. 8. Card RT, and Brain MC: The "anemia" of childhood, N Engl J Med 288:388, 1973.
