• Reduction in circulating red blood cell (RBC) mass
• presents with signs and symptoms of hypoxia
• weakness, fatigue and dyspnea
• pale conjunctiva and skin
• headache and lightheadedness
• angina, especially with preexisting coronary artery disease
• Hb, Hct, and RBC are used as surrogates for RBC mass, which is difficult to measure
• Anemeia <13.5 g/dL in males and <12.5 g/dL in females (normal Hb is 13.5-17.5 in males and 12.5-16g/dL in females)
• Based on MCV, anemia can be classified as microcytic (MCV <80 um, normoctic MCV 80-100 um) or macrocytic MCV>100 um)

• MCV <80
• Microcytic anemias are due to decreased prod. of Hb
• RBC progenitor cells in the bone marrow are large and normally divide multiple times to prod. smaller mature cells (MCV=80-100)
• Macrocytosis is due to an extra division which occurs to maintain hemoglobin concetration
• Hemoglobin is made of heme and globin; heme is composed of iron and protoporphyrin.  A decrease in any of these components leads to microcytic anemia
• Microcytic anemias inclue 1)iron deficiency anemia 2)anemia of chronic disease 3)Sideroblastic anemia, and 4)Thalassemia

• b/c of decreased levels of iron
• decreased iron-->decreased heme-->decreased hemoglobin-->microcytic anemia
• most common type of anemia since lack of iron is the most common nutritional def. in the world, affecting ~1/3 of world's population
• Iron is consumed in heme (meat-derived) and non-heme (vegetable-derived) forms
• absorption occurs in the duodenum.  Enterocytes have heme and non-heme (DMT1) transporters; the heme form is more readily absorbed
• Enterocytes transport iron across the cell membrane into blood via ferroportin
• transferrin transports iron in the blood and delivers it to liver and bone marrow macrophages for storage
• Stored intracellular iron is bound to ferritin, which prevents iron from forming free radicals via the fenton reaction

Lab measurements

• serum iron--measure of iron in the blood
• TIBC-measure of transferrin molecules in the blood
• 3% saturation-percentage of transferrin molecules that are bound by iron (normal is 33%)
• serum ferritin-- reflects iron stores in macrophages and the liver

Caused by:

1. Infants-breast-feeding (human milk is low in iron)
2. children-poor diet
3. adults (20-50 years) peptic ulcer disease in males and menorrhagia or pregnancy in femals
4. elderly- colon polyps/carcinoma in the western world; hookworm (ancylostoma duodenale and Necator americanus) in the developing world
5. Other causes include malnutrition, malabsorption, and gastrectomy (acid aids iron abs. by maintaining the Fe2+ state, which is more readily absorbed than Fe3+)

Stages of Iron Def

1. Storage iron is depeleted-->decreased ferritin: Increased TIBC
2. decreased serum iron-->decreased serum iron and decreased % saturation
3. Normocytic anemia-- Bone marrow makes fewer, but normal sized, RBCs
4. Microcytic, hypochromic anemia--bone marrow makes smaller and fewer RBCs

Clinical findings:anemia, koilonychia , and pica

Lab findings:

1. Microcytic, hypochromic RBCs with increased RBC distribution width
2. decreased ferritin; increased TIBC; decreased serum iron; decreased % saturation
3. Increased Free erythrocyte protoporphyrin (FEP)
4. Treatment involves supplemental iron (ferrous sulfate
5. Plummer-Vinson Syndrome is iron deficiency anemia w/ esophageal web and atrophic glossitis; presents with anemia, dysphagia, and beefy-red tongue

• Red cell distribution width (abbreviated as RDW) is a measurement of the amount that red blood cells vary in size. Red blood cells help carry oxygen in the blood.
• This is not the width of the RBC! (that is measured with the MCV)
  
• A high RDW (over 14.5%) means that the red blood cells vary a lot in size. There are many possible reasons why the RDW level can be too high. (
  

• Anemia associated with chronic inflammation (ex endocarditis or autoimmune conditions) or cancer; most common type of anemia in hospitalized patients
• Chronic disease results in production of acute phase reactants from the liver, including hepcidin
• Hepcidin sequesters iron in storage sites by 1) limiting iron transfer from macrophages to erythroid precursors and 2) suppressing erythropoietin(EPO)production; aim is to prevent bacteria from accessing iron, which is necessary for their survival
• a decrease in available iron--> decrease in heme-->decrease in hemoglobin-->microcytic anemia

• Lab. findings include:
• Increased ferritin, decreased TIBC, decreased serum iron, and decreased % saturation
• Increased free erythrocyte protoporphyrin (FEP)
• Treatment involves addressing the underlying cause; exogenous EPO is useaful in a subset of patients, especially those with cancer

• Anemia due to defective protoporphyrin synthesis
• decreased protoporphyrin-->decreased heme-->decreased hemoglobin-->microcytic anemia
• Protoporphyrin is synthesized via a series of reactions
• Aminolevulinic acid synthtase (ALAS) converts succinyl CoA to aminolevulinic acid (ALA) using vitamin B6 as a cofactor (rate limiting step)
• Aminolevulinic acid dehydrogenase (ALAD) converts ALA to porphobilinogen
• Additional reactions converts porphobilinogen to protoporphyrin
• Ferrochelatase attaches protoporphyrin to iron to make heme (final reaction: occurs in the mitochondria)
• Iron is transferred to erythroid precurors and enters the mitochondria to form heme.  If protoporphyrin is deficient, iron remains trapped in mitochondria.
• Iron-laden mitochondria form a ring around the nucleus of erythroid precursors; these cells are called ringed sideroblasts (hence the term sideroblastic anemia)
• Sideroblastic anemia can be congenital or acquired.
• Congenital defect most commonly involves ALS (rate-limiting enzymes)
• Acquired causes incled--Alcoholism--Mitochondrial poison
• Lead poisoning- Inhibits ALAD and ferrochelatase
• Vitamin B6 def.-- Required cofactor for ALAS; most commonly seen as a side effect of isoniazid treatment for TB
• Lab. findings include increased ferritin, decreased TIBC, increased serum iron, and increased % saturation (iron overloaded state)

• Anemia due to decreased synthesis of the globin chains of hemoglobin
• decreased globin-->decreased Hb-->microcytic anemia
• Inherited mutation; carriers are protected against Plasmodium falciparum malaria
• Divided into alpha and beta thalassemia based on decreased prod. of alpha or beta globin chains
• Normal types of Hb are HbF (alpha 2 gamma 2), HbA (alpha 2 beta 2) and HbA2 (alpha 2, delta 2)

• Due to gene deletion; normally, 4 alpha genes are present on chromosome 16
• one gene deleted=asymptomatic
• two genes deleted-mild anemia with increased RBC count; cis deletion is assoc. w/ an increased risk of sever thalassemia in offspring
• Cis deletion is when both deletions occur on the same chromosome, seen in asians
• trans deletions is when one deletion occurs on each chromosome; seen in Africans, including African Americans
• 3 genes deleted-- sever anemia; beta chains form tetramers (HbH) that damage RBCs; HbH is seen on electrophoresis
• Four genes deleted--lethal in utero (hyrops fetalis) gamma chains form tetramers (Hb Barts) that damage RBCs; Hb Barts is seen on electrophoresis

• Usually due to gene mutations (point mutations in promotor or splicing sites); seen in individuals of African and Mediterranean descent
• Two beta genes are present on chromosome 11; mutations result in absent (beta o) or diminished Beta + production of the beta/globin chain

• (Beta/Beta + is the mildest form of disease and is usually asymptomatic with an increased RBC count.
• Microcytic, hypochromic RBCs and targe cells are seen on blood smear
• Hemoglobin electrophoresis shows slightly decreased HbA with increased HbA2 (5%, normal 2.5 %) and HbF (2%, normal 1%)

• Beta o/Beta o is the most severe form of disease and presents with severe anemia a few months after birth.  High birth HbF (alpha 2, gamma 2) at birth is temporarily protective
• Alpha tetramers aggregate and damage RBCs, resulting in ineffective erythropoiesis and extravascular hemolysis (removal of circulating RBCs by the spleen).
• Massive erythroid hyperplasia ensues resulting in 1)expansion of hematopoiesis into the skull (reactive bone formation leads to crewcut appearance on xray, and facial bones (chipmunk facies). 
• Extramedullary hematopoiesis with hepatosplenomegaly,
• risk of aplastic crisis with parvovirus B19 infection of erythropoid precursors
• Chronic transfusions are often necessary; leads to risk for secondary hemochromatosis
• smear shows microcytic, hypochromic RBCs w/ target cells and nucleated RBCs
• Electrophoresis shows little or no HbA with increased HbA2 and HbF

• Anemia with MCV >100 um; most commonly due to folate or vitamin B12 def. (megaloblastic anemia)
• folate and vitamin B12 are nec. for syn. of DNA precursors
• Folate circulates in the serum as methyltetrahydrofolate (Methyl THF); removal of the methyl group allows for participation in the synthesis of DNA precursors
• Methyl group is transferred to vitamin B12 (cobalamin)
• Vitamin b12 then transfers it to homocysteine, producing methionine
• Lack of folate or vitamin B12 impairs synthesis of DNA precursors
• Impaired division and enlargement of RBC precursors leads to megaloblastic anemia
• Impaired division of granulocytic precursors leads to hypersegmented neutrophils
• MEgaloblastic change is also seen in rapidly-dividing (ex intestinal) epithelia cells
• Other causes of macrocytic anemia (w/o megaloblastic change) include alchoholism, liver disease, and drugs

• Dietary folate is obtained from green vegetables and some fruits
• absorbed in the jejunum
• Folate def. develops w/i months, as body stores are minimal
• causes include poor diet (ex alcoholics and elderly), increased demand (ex pregnancy, cancer, and hemolytic anemia), and folate antagonists (e.g. methotrexate, which inhibits dihydrofolate reductase)
• Clinical and laboratory findings include

1. Macrocytic RBCs and hypersegmented neutrophils (>5 lobes)
2. Glossitis
3. Decreased serum folate
4. Increased serum homocysteine (increases risk for thrombosis)
5. Normal methylmalonic acid

• Dietary B12 is complexed to animal-derived proteins
• Salivary gland enzymes eg amylase liberate vitamin B12, which is then bound by R0binder (Also from the salivary gland) and carried through the stomach
• pancreatic proteases in the duodenum detach vitamin B12 from R-binder
• Vitamin B12  binds intrinsic factor (made by gastric parietal cells) in the small bowel; the intrinsic factor-vitamin B12 complex is absorbed in the ileum
• Vitamin b12 deficiency is less common than folate deficiency and takes years to develop due to large hepatic stores of vitamin B12
• Pernicious anemia is the most common cause of vitamin B12 def.--autoimmune destruction of parietal cells (body of stomach) leads to intrinsic factor deficiency
• Other causes of vitamin B12 def. include pancreatic insufficiency and damage to teh terminal ileum (ex Crohn disease or Diphyllobothrium latum [fish tapeworm] dietary def. is rar, except in vegans
• Clinical and lab findings include
• Macrocytic RBCs w/ hypersegmented neutrophils
• Glossitis
• Subacute combined degeneration of the spinal cord
• Vitamin B12 is a cofactor for the conversion of methylmalonic acid to succinyl CoA (imp. in fatty acid metabolism)
• Vitamin B12 def. results in increased levels of methylmalonic acid which impairs spinal cord myelinization
• Damage results in poor proprioception and vibratory sensation (posterior column) and spastic paresis (lateral corticospinal tract)
• decreased serum vitamin B12
• increased serum homocysteine( similar to folate def.), which increases risk for thrombosis
• Increased methylmalonic acid (unlike folate def)

• Anemia w/ normal sized RBCs (MCV=80-100um^3)
• Due to increased peripheral destruction or underproduction
• Reticulocyte count helps to distinguish between these two etiologies

• Young RBCs released from the bone marrow
• identified on blood smear as larger cells with bluish cytoplasm (due to residual DNA)
• Normal reticulocyte count (RC) is 1-2%
• RBC lifespan is 120 days; each day roughly 1-2 % of RBCs are removed from circulation and replaced by reticulocytes
• A properly functioning marrow responds to anemia by increasing the RC to >3%
• RC, however is falsly elevated in anemia.
• RC is measured as a percentage of total RBCs; decrease in total RBCs falsly elevates percentage of reticulocytes
• RC is corrected by multiplying reticulocyte count by Hct/45
• Corrected count >3% incdicated good marrow response and suggests peripheral destruction
• Corrected count <3% indicates poor marrow response and suggests underproduction

• Autosomal recessive mutation in beta chain of hemoglobin; a single amino acid change replaces normal glutamic acid (hydrophilic) with valine (hydrophobic)
• gene is carried by 10% of individuals of African descent, likely due to protective role against falciparum malaria
• Sickle cell disease arises when two abnormal beta genes are present; results in >90 % HbS in RBCs
• HbS polymerizes when deoxygenated; polymers aggregat into needle-like structures, resulting in sickle cells
• Increased risk of sickling occurs with hypoxemia, dehydration, and acidosis
• HbF protects against sickling; high HbF at birth is rprotective for the first few motnhs of life.  Treatment with hydroxyurea increases levels of HbF
• Cells continuously sickle and de-sickle while passing through the microcirculation, resulting in complications related to RBC membrane damage
• Extravascular hemolysis- Reticuloendothelial system removes RBCs with dmaged membranes, leading to anemia, jaundice w/ unconjugated hyperbilirubinemia, and increased risk for bilirubin gallstones
• Intravascular hemolysis-- RBCs with damage membranes dehydrate, leading to hemolysis with decreased haptoglobin and target cells on blood smear
• massive erythroid hyperplasia ensues resulting in :
• expansion of hematopoiesis into the skull and facial bone (crewcut and chipmunk face)
• Extramedullary hematopoiesis with hepatomegaly
• risk of aplastic crisis w/ parvovirus B19 infection of erythroid precursors
• Irreversible sickling leads to complications of vaso-occlusion
• Dactylitis-swollen hands and feet due to vaso-occlusive infarcts in bone; common presenting sign in infants
• autosplenectomy-shrunken, fibrotic splee.  Consequences include:
• Increased risk of infection with encapsulated organisms such as streptococcus pneumoniae and Haemophilus influenzae (most common cause of death in children); affected children should be vaccinated by 5 years of age
• increased risk of Salmonella paratyphi osteomyelitis
• Howell-Jolly bodies on blood smear

• Acute chest syndrome-- Vaso-occlusion in pulmonary microcirculation
• presents with chest pain, shortness of breath, and lung infiltrates
• often precipitated by pneumonia
• most common cause of death in adults
• Pain crisis
• Renal papillary necrosis-results in gross hematuria and proteinuria
• Sickle cell trait is the presence of one mutated and one normal beta chain; results in <50% HbS in RBCs (HbA is slightly more eff prod. than HbS)
• Generally asymptomatic w/ no anemia; RBCs w/ <50% HbS do not sickle in vivo except in the renal medulla
• Extreme hypoxia and hypertonicity of the medulla cause sickling, which results in microinfarctions leading to microscopic hematuria and, eventually decreased ability to concentrate urin

Lab findings:

• Sickle Cells and target cells are seen on blood smear in sickle cell disease, but no in sickle cell trait
• metabisulfate screen causes cells w/ any amt of HbS to sickle; positive to both disease and trait
• Hb electrophoresis confirms the presence and amt of Hb S
• Disease 90% HbS, 8% HbF, 2% HbA2 (No Hb A)
• Trait 55% HbA, 43% HbS, 2% HbA2

• Divided into extravascular and intravascular hemolysis; both result in anemia w/ a good marrow response
• Extravascular hemolysis involves RBC destruction by the reticuloendothelial system (macrophages of the spleen, liver and lymphy nodes)
• macrophages consume RBCs and break down hemoglobin
• globin is broken down into AAs
• heme is broken down into iron and protoporphyrin; iron is recycled
• protoporphyrin is broken down into unconjugated bilirubin, which is bound to serum albumin and delivered to the liver for conjugation and excretion into bile

• clin and lab findings:
• Hemoglobinemia
• Hemoglobinuria
• hemosiderinuria-Renal tubular cells pick up some of the hemoglobin that is filtered into the urine and break it down into iron, which accumulates as hemosiderin; tubular cells are eventually shed resulting in hemosiderinuria
• decreased serum haptoglobin

• Basic Principles
• Decreased prod. of RBCs by bone marrow; char by low corrected reticulocyte count
• Etiologies include:
• causes of microcytic and macrocytic anemia
• Renal failure-decreased prod. of EPO by peritubular interstitial cells
• Damage to bone marrow precuros cells (may result in anemia or pancytopenia)

• Inherited defect of RBC cytoskeleton-membrane tetherine proteins
• Mostcommonly involves spectrin, ankyrin, or band 3.1
• Membrane blebs are formed and lost over time
• Loss of membrane renders cells round (spherocytes) instead of disc-shaped
• spherocytes are less able to maneuver through splenic sinusoids and are consumbed by splenic macrophages, resulting in anemia
• Clinical and lab findings include
• spherocytes w/ loss of central pallow
• increased RDW adn increased mean corpuscular hemoglobin concentration (MCHC)
• splenogmegaly, jaundice with unconjugated bilirubin, and increased risk for bilirubin gallstones (Extravascular hemolysis)
• increased risk for aplastic crisis with parvovirus B19 infection of erythroid precursors
• Diagnosed  by osmotic fragility test, which reveals increased spherocyte fragility in hypotonic solution
• Treatment is splenectomy; anemia resolves, but spherocytes persist and Howell-Jolly Bodies (Fragments of nuclear material in RBCs emerge on blood smear)

• Autosomal recessive mutation in beta chain of hemoglobin
• Normal glutamic acid is replaced by lysine
• less common than sickle cell disease
• presents with mild anemia due to extravascular hemolysis
• Char. HbC crystals are seen in RBCs on blood smear

• Acquired defect in myeloid stem cells resulting in absent glycosylphosphatidylinositol (GPI); renders cells susceptible to destruction by complement
• Blood cells coexist with complement
• decay accelerating factor (DAF) on the surface of blood cells protects agains complement-mediated damage by inhibiting C3 convertase
• DAF is secured to the cell membrane by GPI (an anchoring protein)
• Absence of GPI leads to absence of DAF, rendering cells susceptible to complement-mediated damage
• Intravascular hemolysis leads to hemoglobinemia and hemoglobinuria (esp. in the morning) hemosiderinuria is seen days after hemolysis
• sucrose test is used to screen for disease; confirmatory test is the acidified serum test or flow cytometry to detect lack of CD55 (DAF) on blood cells
• Main cause of death is thrombosis of the hepatic, portal, or cerebral veins
• Destroyed platelets release cytoplasmic contents into circulation, inducing thrombosis
• Complications include iron def. anemia (due to chronic loss of hemoglobin in the urine) and acute myeloid leukemia (AML), which develops in 10% of patients

• X linked recessive disorder resulting in reduced 1/2 life of G6PD; renders cells susceptible to oxidative stress
• RBCs are normall exposed to oxidative stress, in particular H2O2
• Glutathione (an antioxidant) neutralizes H2O2, but becomes oxidized in the process
• NADPH, a by product of G6PD, is needed to regenerate reduced glutathione
• Decreased G6PD-->decreased NADPH-->reduced glutathione-->oxidative injurty by H2O2-->intravascular hemolysis
• G6PD has 2 variants
• African variant-mildly reduced t1/2 of G6PD leading to mild intravascular hemolysis with oxidative stress
• Mediterranean variant-markedly reduced half life of G6PD leading to marked intravascular hemolys with oxidative stress
• High carrier frequency in both populations is likely due to protective role against falciparum malaria
• Oxidative stress precipitates Hb as Heinz bodies
• causes of oxidative stress include infections, drugs (ex primaquin, sulfa drugs, and dapsone), and fava beans
• Heinz bodies are removed from RBCs by splenic macrophages, resultin in bite cells
• leads to pred. intravascular hemolysis
• Presents with hemoglobinuria and back pain hours after exposure to oxidative stress
• Heinz preparation is used to screen for disease (precipitated hemoglobin can only be seen w/ a special heinz stain)
• Enzyme studies confirm def. (performed weeks after hemolytic episode resolves)

• Antibody-mediated (IgG or IgM) destruction of RBCs
• IgG-mediated disease usually involves extravascular hemolysis
• IgG binds RBCs in the relatively warm temperature of the central body (warm agglutinin); membrane of antibody-coated RBC is consumed by splenic macrophages resulting in spherocytes
• Associated w/ SLE (most common cause), CLSS, and certain drugs (classically penicillin and cephalosporins)
• Drug may attach to RBC membrane (ex peniclillin) w/ subseqent binding of antibody to drug membrane-complex
• Drug may induce prod. of autoantibodies (ex alpha methyldopa) that bind self antigens on RBCs
• Treatment involves cessation of the offending drug, steroids, IVIG, and if necessary, splenectomy.
• IgM-mediated disease usually involves intravascular hemolysis
• IgM binds RBCs and fixes complement in the relatively cold temperature of the extremeties (cold agglutinin)
• Associated w/ Mycoplasma Pneumonia and infectious mononucleosis
• Coombs test is used to diagnose IHA; testing can be direct or indirect
• Direct Coombs test confirms the presnec of antibody-coated RBCS, Anti-IgG is added to patient RBCS, agglutination occurs if RBCs are already coated w/ antibody.  This is the most important test for IHA
• Indirect Coombs test confirms the presence of antibodies in patient serum.  Anti-IgG and test RBCs are mixed with the patient serum; agglutination occurs if serum antibodies are present

• Intravascular hemolysis that results from vascular pathology; RBCs are destroyes as they pass through the circulation
• Iron def. Anemia occurs with Chronic hemolysis
• Occurs with microthrombi (TTP-HUS, DIC, HELLP), prosthetic heart valves and aortic stenosis, microthrombi produce schistocytes on blood smear

• Infection of RBCs and liver with Plasmodium; transmitted by the female Anopheles mosquito
• RBCs rupture as a pare of the plasmodium life cycle, resulting in intravascular hemolysis and cyclical fever
• P. falciparum-daily fever
• P vivax and P ovale-- fever every other day
• Splee also consumes some infected RBCs; results in mild extravascular hemolysis w/ splenomegaly

• Infects progenitor red cells and temporarily halts erythropoiesis; leads to sig. anemia in the setting of preexisting marrow stress (ex sickle cell anemia)
• Treatment is supportive (infection is self-limited)

• Damage to hematopoietic stem cells, resulting in pancytopenia (anemia, thrombocytopenia, and leukopenia) with low reticulocyte count
• Etiologies include drugs or chemicals, viral infections, and autoimmune damage
• Biopsy reveals an empty, fatty marrow
• Treatment includes cessation of any causative drugs and supportive care w/ transfusions and marrow-stimulating fators (ex erythropoietin, GM-CSF, and G-CSF)/
• Immunosuppression may be helpful as some idiopathic cases are due to abn. T-cell act. w/ release of cytokines
• May req. bone marrow transplantation as a last resort