IRON DEFICIENCY ANEMIA

F.A. Rice,  ART, CLS  
March 1, 1996
Please send comments to: F.A. Rice
This lecture will concentrate on iron deficiency anemia.  For 
discussion on anemia in general refer to the University of Washington or 
the Healthnet.  
Iron deficiency anemia is the most common anemia in the world. 
Iron is an essential component of the hemoglobin molecule, without 
iron the marrow is unable to produce hemoglobin. The red cell 
number falls and those which do reach the circulation are smaller 
than normal (microcytic) and lack hemoglobin, hence they are pale 
and under colored (hypochromic).  The deficiency in iron may be
absolute, that is, there is no iron available for the production of 
hemoglobin, this is true iron deficiency anemia.  The deficiency 
may be relative, that is, the iron is present in storage in the 
marrow but is unavailable for hemoglobin production, this is anemia 
of chronic disease.
Outline:
Normal Iron Physiology
1. Total Body Iron

The amount of iron present varies with the body size, age and sex 
of the individual. 	   


2. Iron sources and balance

The average normal North American diet contains approximately 
15-20 mg of iron.  Most is present in meat and green vegetables. 
Approximately 1.0 mg is absorbed each day and just about an equal 
amount is lost in the feces and sweat.  As a result, the average 
adult is in a tenuous state of balance.  This delicate balance is 
of little consequence as there is slightly more iron absorbed than 
lost and a store of iron is accumulated.  If, however, the rate of 
iron loss increases, usually through blood loss such as chronic 
bleeding, these stores can be depleted and an absolute iron deficiency
develops.
3. Iron distribution

The majority of the iron present is present as hemoglobin iron. 
Approximately 25% of the iron is maintained as storage iron 
(ferritin and hemosiderin) primarily in the bone marrow. 	  
     - hemoglobin          65 to 70%         1.5 to 3.0 gm  	  
     - storage
          ferritin   	                    
          hemosiderin      20 to 30%         0.5 to 1.5 gm   	
     - other
          myoglobin      	               
          heme enzyme      remainder
4. Iron absorption
  	  
Iron absorption occurs primarily in the duodenum.  Most of this 
iron is in the ferric (+++) form and is complexed to other organic 
and inorganic molecules.  The acid in the stomach and hydrolytic 
enzymes in the small  intestine release the iron from these 
complexes. 	It is then reduced to the ferrous (++) form as it is 
more readily absorbed in this state.   Absorption is increased by 
the presence of:
     glucose
     fructose
     some amino acids
     ascorbic acid (Vitamin C)
These substances aid in the absorption process by either reducing 
ferric iron to the ferrous state or by helping bind the iron to the 
mucosal cell receptor sites.  It is recognition of the positive 
effects of vitamin C which has resulted in many iron supplements 
being manufactured with this vitamin present. 	Heme iron, iron in 
meat myoglobin, is more easily absorbed than elemental iron. 	Iron 
absorption is decreased by the presence of:
     phosphate
     bicarbonate
     bile acids
Once the ferrous iron (++) binds to receptors on the surface of 
mucosal cells it is moved into the cell. This is an energy dependent
process. 	In the mucosal cell the iron is oxidized back to the 
ferric (+++) state and bound to apoferritin in the cell.  This 
continues until all the apoferritin bound at which point newly 
absorbed iron is no longer oxidized but rather is passed through 
the cell and into the portal circulation still in the ferrous 
state. In the blood, iron is bound to transferrin in the ferric 
state.  Bound to transferrin, the iron is transported to the marrow 
for use or storage.
5. Regulation of iron absorption
 	  
The intestinal wall is covered with villi, finger-like projections, 
which are covered with absorptive mucosal cells. These cells are 
produced in the crypts of Lieberkhun, at the base of the villi, and 
move upwards to the villus tip to be disquamated (lost). Each cell 
is produced with a set amount of apoferritin.  The more iron 
required by the body the less apoferritin  manufactured in each 
cell.  In other words, it is the amount of apoferritin within each 
mucosal cell which acts as the gatekeeper and regulates the amount 
of iron absorbed.
6. Iron transport

Transferrin is the primary iron transport protein.  It is a beta 
globulin and is produced in liver.  It has a 1/2 life of 8-11 days. 
 Each molecule of transferrin can bind and transport two molecules 
of iron in the ferric (+++) state.    Transferrin prefers to carry 
iron to the marrow but will carry iron to other organs if the 
marrow is damaged or excess amounts of iron are already stored in 
the marrow.  In rare instances when transferrin is absent 
(atransferrinemia)  other proteins can bind iron but carry the iron 
to other organs such as liver, spleen and pancreas, little if any 
is carried to the marrow.   As well as specific receptors for iron, 
transferrin has specific receptors for sites on the developing 
normoblast and RE cell.   Once bound to the cell membrane, the 
transferrin changes shape and releases the iron.  It then returns 
to the portal circulation to bind more iron. Under normal circumstances
approximately 1/3 of the transferrin has iron bound to it.
7. Iron transfer across the Red Cell membrane

Iron can be transfered to developing red cells either bound to 
transferrin or presented as ferritin to the developing cells as 
they cluster around "nurse cell" RE cells. The iron is moved into 
the developing red cell by a process similar to pinocytosis called 
ropheocytosis. Clusters of normoblasts around a nurse cell are 
called a "feed islands".
8. Iron storage

Iron is stored as either ferritin or hemosiderin.
-ferritin  consists of an outer protein shell with iron complexed 
within the core.  The outer shell consists of 22 apoferritin 
molecules while the core consists of an iron/phosphate complex 
consisting of 4,000 to 5,000 molecules of iron in each core. 
 Ferritin is water soluble and a very small amount is dissolved in 
the plasma. The more ferritin stored the more dissolved in the 
plasma.  The ferritin reference range for males is  40 to 300 ug/l 
and 20 to 150 ug/l for females.  Ferritin is not visible by light 
microscopy, nor is it stained by the Prussian Blue reaction.  It is 
preferentially used before hemosiderin, probably because it is 
soluble.              
-hemosiderin is aggregated ferritin molecules. The protein shell 
has been altered and as a result it is water insoluble.  It can be 
seen by light microscopy as gold-brown granules and is demonstrated 
by the Prussian Blue stain.
9. Daily Iron Requirements

The adult male requires approximately 1.0 mg/day. Just enough to 
cover normal iron loss.  The adult female requires approximately 
2.0 mg/day.  Enough for daily loss and menstruation.  Pregnant 
females require approximately 3.0 mg.  Enough for normal, on going 
loss and fetal requirements.  Children require approximately 
2.0 mg/day. Enough for normal loss and extra to produce some 
residual iron stores and allow for increasing red cell mass.
10. Causes of Iron Deficiency
chronic blood loss is the most common cause of iron deficiency anemia.
Iron deficiency anemia
Development of anemia
	
It must be remembered that anemia in iron deficiency develops 
slowly. The type and severity of the anemia varies with time. 

Development Stages:

Laboratory Diagnosis of Iron Deficiency

Routine procedures
Hgb, Hct and RBC count are all decreased. The degree of decrease 
depends upon the length of time the marrow has been without 
sufficient supplies of iron. It must be remembered that at any 
stage the red cell number will not be proportionately as low as is 
the Hgb and Hct. This is due to the fact that the marrow can 
continue to produce empty cells.
Indices - MCV - decreased, MCH - decreased, MCHC - decreased. 
The MCHC is the last to become lowered. This is due to the fact that
as the marrow becomes more and more depleted of iron it produces 
smaller cells with a smaller amount of hemoglobin in each in an 
attempt to keep the concentration of hemoglobin in each normal. The 
RDW is increased which reflects the anisocytosis characteristic of 
iron deficiency.
Morphology - changes from normal to simple microcytic to 
hypochromic microcytic as the iron deficiency progresses. When full 
blown there is marked anisocytosis and poikilocytosis with 
elliptocytes and target cells. 	NRBC may be seen on a rare 
occasion.
White cell count and differential - normal
Platelets - normal to increased. They are usually microcytic 
and stain very pale and can be missed on film.
Retics - the relative count is decreased to normal while the production index (PI) is  decreased.
Special procedures
A bone marrow examination is seldom, if ever, performed or needed 
for the diagnosis of an iron deficiency anemia.  If however, a bone 
marrow is performed the following results would be present.
Bone Marrow 
cellularity - normal to increased
morphology - normoblastic with some dyserythropoiesis. Ragged 
reduced cytoplasm, vacuoles, multinuclearity, karryohexis, nuclear 
budding, abnormal mitosis.  All these may be seen but are not the 
predominant features of the marrow.

iron stain - absent.  The absence of iron is considered to be the 
"gold standard" for the diagnosis of iron deficiency. 

siderocytes - absent
Serum iron - decreased 	
TIBC - increased 	
%saturation - decreased 	
Ferritin - decreased 	
Free erythrocyte protoporphyrin (FEP) - increased


NOTE!  The above review provides strong 
evidence for using serum ferritin as an initial laboratory test for 
the evaluation of iron deficiency anemia.


Bilirubin - normal to decreased
Treatment

Iron supplement. The response is monitored with the retic count, 
 hemoglobin and hematocrit.                                                                            A failure to respond may be due to: