Red Blood Cell

Describe Blood Cell Lineage

HSC: Myeloid or Lymphoid

Myeloid: Erythroblast, Myeloblast (Granulocyte), Monoblast, Megakaryoblast

Lymphoid: B Cell, T Cell

What is RBC formation stimulated by?

Erythropoietin

During formation, how long does it take for a reticulocyte to be released into the blood?

5-7 days

How long does it take for reticulocytes to become mature RBCs?

1-2 days

How long is a normal RBC in circulation for?

120 days (then removed by the spleen)

Why is the cytoplasm of reticulocytes "bluer" than RBCs?

There is still a little bit of RNA present

What is the job of the RBC?

transport O2 and CO2

What are the characteristics of hemoglobin in respect to O2?

binds O2 avidly at high O2 pressure (lungs)

releases O2 readily at low O2 pressure (tissues)

What are the steps in RBC formation/maturation?

Proerythroblast (very blue) -> basophilic normoblast (blue) -> polychromatic normoblast -> orthochromatic normoblast (loses nucleus)-> reticulocyte -> erythrocyte (RBC)

WHat is the structure of hemoglobin?

4 globin chains, each bound to a heme molecule containing iron (Fe)

What is the structure of fetal hemoglobin (HbF)?

2 alpha

2 gamma

HbF

What is the structure of most (95%) of the adult hemoglobin (HbA)?

2 alpha

2 beta

HbA

What is the structure of the minor (2%) hemoglobin type found in adults (HbA2)?

2 alpha

2 delta

HbA2

What are 2 reasons that are RBCs biconcave disks?

allow more surface area for O2 binding

allow flexibility and easy passage through capillaries and splenic sinusoids

What is anemia?

reduction in circulating red cell mass

How is anemia measured/determined?

from hemoglobin concentration & hematocrit (packed cell volume)

What are the symptoms of anemia?

decreased RBC = hypoxia

weakness

fatigue

dyspnea, short of breath on exertion

pale conjunctive and skin

headache, dizziness, light headed, fainting

angina (low O2 delivery to the heart)

What are the signs of anemia?

increased pulse rate

increased respiratory rate

increased stroke volume (eventual cardiac failure)

pallor and nail changes (if severe)

Mean Cell Volume (MCV)

Average volume of an RBC

(can appear normal if there are lots of too small RBCs and too large RBCs, they will balance out, but RDW will be increased)

MEan Cell HEmoglobin (MCH)

average content of hemoglobin per RBC

Mean Cell Hemoglobin Concentration (MCHC)

average concentration of hemoglobin in a given volume of packed RBCs

Red Cell Distribution Width (RDW)

coefficient of variation of RBC volume

Give an example of when Hb and Hct would be decreased physiologically:

Pregnancy

woman has normal RBC mass but her blood volume is increased so much that the Hb and Hct concentration will decreased because they are being diluted

Give an example of when Hb and Hct would be decreased due to trauma:

Gun shot wound

massive blood loss, give fluid to maintain blood pressure, Hct and Hb are normal but when you give fluid they will be diluted and appear decreased

How are anemias classified morphologically?

Color (degree of "pinkness"): normo or hypo

Size (MCV): micro, normo, macro

Shape: Sphero, Sickle (pencil cells, helmet cells, etc.)

If there was poikilocytosis how would the RDW look?

increased

cells of all different shapes and sizes

The pale area, "donut hole", in the RBC should be how large?

1/3 of the cell size

How are anemias classified by underlying mechanism?

Peripheral: accelerated loss or destruction (spleen, vessels, or peripheral hemorrhage)

Central: impaired production (bone marrow)

What are the 2 ways anemia can occur due to blood loss?

Acute Hemorrhage (usually in trauma or accident and the immediate concern is still hypovolemia)

Chronic Blood Loss (rate of loss exceeds production or when iron stores are depleted, menstruation, blood in stools from colon lesion, etc.)

What are 3 main features of hemolytic anemia?

1) shortened RBC lifespan (

What are the two sites that hemolysis occurs?

Extravascular (spleen)

Intravascular

Which is more likely, intravascular or extravascular hemolysis?

extravascular

What are 3 causes of intravascular anemia?

1) Mechanical injury to RBCs (defective heart valves, thrombi)

2) Complement fixation of antibody coated RBCs

3) Infections (intracellular parasites like malaria or toxins like clostridia)

What causes extravascular hemolysis to occur?

RBCs less deformable (spherocytosis or sickle cell)

RBCs rendered "foreign" by autoimmune disease Abs

What are the classifications of Mean Cell Volume (MCV)?

normocytic is 80 -100

microcytic < 80, macrocytic > 100

What is seen in the peripheral blood in hemolytic anemia?

macrocytic with polychromasia due to increased reticulocytes

(bone marrow rapidly trying to compensate)

WHat is seen in the bone marrow in hemolyctic anemia?

Erythroid hyperplasia

What is seen in the plasma/serum in hemolytic anemia?

Increased unconjugated bilirubin (due to RBC lysis)

Increased free hemoglobin

Increased LDH (lactate dehydrogenase, anaerobic glycolysis)

Decreased or absent haptoglobin (it is used up trying to scavenge all of the free heme)

What will be seen in the urine in intravascular hemolysis?

hemosiderinuria

hemoglobinuria

What are the causes of intrinsic hemolytic anemia?

Membrane defect: Hereditary Spherocytosis

Enzyme Defect: G6PD Def. & PNH

Hemoglobin Defect: Sickle Cel, Thalassemia

What are the causes of extrinsic hemolytic anemia?

Immune damage: autoimmune & drugs

Non-immune damage: trauma, infections, chemicals

Sequestration: hypersplenism (very large spleen)

What is the inheritance pattern of Hereditary Spherocytosis?

Autosomal Dominant

What is the average lifespan of an RBC in Hereditary Spherocytosis?

10-20 days

What happens to RBCs in Hereditary Spherocytosis?

Abnormalities in membrane proteins -> lose the ability to tether the membrane in to form the biconcave shape -> cells become more sphere shaped as they age -> less flexible -> loss of small fragments due to shearing -> they will be destroyed in the spleen

What are the 3 main membrane proteins affected in Hereditary Spherocytosis?

Ankyrin (75%)

Band 3 (20%)

Spectrin

What happens to the spleen in Hereditary Spherocytosis?

Enlarged (destroying lots of RBCs)

It will look packed full of RBCs and very red

Hypertrophy of macrophages is a key finding

Why is the MCHC increased in Hereditary Spherocytosis?

RBCs get smaller due to shearing but have the same amount of Hb so the concentration rises

Why is the RDW increased in Hereditary Spherocytosis?

RBCs get smaller from shearing (old cells), some are still sphere shaped and normal volume (young cells), and the erythroid hyperplasia in the bone marrow puts out reticulocytes that are larger

What is the anemia like in Hereditary Spherocytosis?

mild to moderate (25% asymptomatic)

chronic

What is a Howell-Jolly Body?

Reticulocyte with small amount of DNA material still present forming an cytoplasmic inclusion within cell

What do the presence of Howell-Jolly bodies indicate?

Asplenia, dysfunctional spleen, or overwhelmed spleen

Seen in Sickle Cell Anemia, Hereditary Spherocyctosis, Myelodysplastic Syndrome

What is aplastic crisis?

Decrease in reticulocytes (RBC precursor)

What virus can cause aplastic crisis in Hereditary Spherocytosis?

Parvovirus B19 (Fifth's Disease)

It invades reticulocytes, halting RBC production

Also seen in Sickle Cell Anemia

What is the Osmotic Fragility Test?

RBCs lyse prematurely when exposed to increasingly hypotonic salt solutions

Spherocytes are already rounded, they have no room to expand with fluid influx, and will lyse faster than normal RBCs

What can be seen in Hereditary Spherocytosis due to the increased unconjugated bilirubin?

jaundice and gall stones

What is Glucose-6-Phosphate Dehydrogenase Deficiency (G6PD)?

Abnormal Hexose Monophosphate Shunt

G6PD enzyme is misfiled and subject to degradation

Reduced t1/2 of enzyme

Young RBCs have functional G6PD & then it degrades (RBCs have no nucleus and can't form more)

What happens without G6PD?

Can not produce NADPH from G6P

Can not reduce GSSG back to GSH (Glutathione) Therefore can not use GSH to reduce H2O2 to H2O

Oxidative damage to RBCs results

What happens to the lifespan of the RBCs?

The older the RBC gets, the more oxidative stress, and it cannot defend against it so will die

What are the 2 variants of G6PD Deficiency that cause clinically significant hemolysis?

African: mild, somewhat reduced t1/2 of G6PD

Middle Eastern: severe, very reduced t1/2 of G6PD

Why is this enzyme defect selected for in the African population?

it is protective against malaria

Plasmodia falciparum

What happens to Hb in RBCs exposed to a lot of oxidant stress?

Heinz Bodies form (need special Heinz prep to see, they appear green)

oxidation of SH (sulfhydryl) groups on Hb

precipitation of denatured globins on RBC membrane

What do Heinz Bodies produce?

Bite Cells and then Spherocytes

How are Bite Cells formed?

Splenic macrophages "bite" out the Heinz Body leaving a chunk of the RBC missing -> eventually the membrane integrity is compromised enough that the RBCs will form spherocytes

Which is more prevalent in G6PD Deficiency, intravascular or extravascular hemolysis?

intravascular

What are signs and symptoms of intravascular hemolysis?

hemoglobinuria and back pain (kidney damage)

What is the inheritance pattern of G6PD Deficiency?

Recessive X-linked

mostly males affected

How does G6PD Deficiency present?

Acute hemolysis, dramatic drop in hemoglobin, 2-3 days after exposure to oxidant stress

Infections

Drugs (sulfa drugs, primaquine, dapsone)

Foods (fava beans)

Neonatal jaundice (rare)

Chronic mild hemolytic anemia lacking cause (rare)

How do you test for G6PD Deficiency?

Enzyme studies

When do you test for the G6PD enzyme to confirm diagnosis of deficiency?

AFTER acute hemolysis resolves

RBCs killed during the episode are the RBCs lacking the enzyme (old), those that remain have the enzyme (young), need to regain normal distribution to detect

What diseases are due to a defective production of hemoglobin?

Hemoglobinopathies

Sickle Cell Anemia and HbC disease

hemoglobin produced is abnormal

What diseases are due to a decreased synthesis of hemoglobin?

Thalassemias (alpha and Beta)

hemoglobin produced is normal, just less

What causes Sickle Cell Anemia?

point mutation in the B globin gene (chromosome 11)

glutamic acid (neg. charge) -> valine (neutral)

produces HbS

What % HbS causes Sickle Cell Trait?

What % of HbS causes Sickle Cell Disease?

90% Homozygous (SS)

What does Sickle Cell Trait protect against?

Malaria

10-30% of people in West Africa are heterozygous

What causes malaria?

Plasmodium falciparum

What is the vector for Plasmodium falciparum?

Anopheles mosquito

What does Plasmodium falciparum infect?

RBCs

causes extravascular and intravascular hemolysis

What is the fever pattern in Plasmodium falciparum?

daily spikes

What is the fever pattern in Plasmodium vivax and ovale?

fever spike every other day

How much HbS do you need for the cells to sickle?

50% or more

That is why heterozygotes don't sickle

What is seen in a peripheral smear of someone with Sickle Cell Disease?

sickled RBCs and target cells

also Howell-Jolly bodies (autosplenectomy in an adult so they won't get removed)

Why does Sickle Cell cause kidney crisis?

renal medulla is always near hypoxic & this can cause RBCs to sickle

decreased ability to concentrate urine

more dehydration will lead to more sickling

What are the steps that cause extravascular hemolysis in Sickle Cell Disease?

repeated sickling over time causes membrane damage so the spleen will remove these abnormal RBCs

What causes cells to sickle?

Deoxygenated HbS molecules will aggregate and polymerize, form needle like structure that cause membrane sickling, repeated occurrences of sickling cause membrane damage which results in an irreversible sickled shape

What factors increase sickling?

Amount of HbS present, more is bad

HbC

Hb concentration from dehydration

Low pH

Length of exposure to hypoxia

What factors decrease sickling?

HbA and HbF

Coexisting alpha Thalassemia (less globin, less Hb)

What is the mutation causing HbC?

point mutation of the B globin gene at position 6

glutamic acid (neg. charge) -> lysine (pos. charge)

What are the clinical features of Sickle Cell Disease?

Chronic hemolysis - intra and extra vascular

Moderate to severe anemia

Hyperplastic bone marrow

Hypersplenism (kids) constant hemolysis

Then repeated infarction & fibrosis leading to autosplenectomy

Encapsulated bacteria infections

Hyperbilirubinemia and gallstones

What can cause a Sickle Cell Crisis?

Infections, dehydration, cold, hypoxia, acidosis

Sequestration crisis (kids) pooling of blood in spleen

What happens in a Sickle Cell Crisis?

microvascular occlusions in bones, brain, lungs, retina, kidneys, legs - PAINFUL

What can cause aplastic crisis?

Parvo B 19 virus

infects red cell precursors

What factors would help to diagnose Sickle Cell Disease?

Family history

Peripheral blood smear

Metabisulfite test (reducing agent will induce sickling)

Hemoglobin electrophoresis (valine makes HbS less negative and it will migrate differently)

DNA Screening (prenatal diagnosis)

How does a Xray of the head look on a child with Sickle Cell Disease?

crew cut appearance and chipmunk cheeks due to extramedullary hematopoiesis

What is the primary cause of death in children with Sickle Cell Disease?

infections with encapsulated bacteria

spleen is ischemia, fibrotic, not functioning

What can happen to the kidneys in Sickle Cell Disease?

Renal Papillary Necrosis

hematuria and proteinuria (resembles nephrotic synd)

caused by lots of microinfarcts over time

What can happen to the lungs in Sickle Cell Disease?

infection/pneumonia causing inflammation

decreased transit time of RBCs through the vessels will increase sickling

chest pain and short of breath

What is the treatment for Sickle Cell Disease?

Rehydration, transfusions, analgesics for crisis phase

Folic acid supplementation

Penicillin prophylaxis for bacterial infections

Hydroxyurea increases HbF and reduces inflammation

Bone marrow transplant

What is the prognosis of Sickle Cell Disease patients with the homozygous trait?

90% survive to age 20 and 50% survive to age 50

Infection is often the cause of death in children

Kidney failure is often the cause of death in adults

What is the cause of Thalassemias?

decreased production on the alpha or Beta globin chain, low levels of normal Hb