W1: Hemolysis

Question 1

What are the 3 functions of hemaglobin?

Answer 1

• Oxygen transport
• CO2 transport from
• Acid-base balance

Question 2

Discuss the oxygen dissociation curve

Answer 2

• The higher the saturation of oxygen eg. lungs; the higher the oxygen tension (for efficient and maximum uptake of excess oxygen to the tissues)
• The lower the saturation of oxygen eg. tissues; the lower the oxygen tension (for efficient delivery of oxygen to the tissues)

*oxygen tension: binding affinity of oxygen to haemaglobin

Question 3

What is haemolysis?

Answer 3

Premature destruction of RBCs

Question 4

Normal red cell life span?

Answer 4

100 – 120 days
~1% red cells destroyed / day

Question 5

Two mechanisms of haemolysis

Answer 5

• intravascular hemolysis
  -extravascular hemolysis

Question 6

What is intravascular haemolysis?

Answer 6

The destruction of RBCs that occurs within the vascular compartment, and red cells contents are released in the plasma.

Question 7

What is extravascular haemolysis?

Answer 7

The destruction of RBCs that occurs outside the vascular compartment; in the spleen, liver or bone marrow. Red cells are taken up and destroyed by macrophages

Question 8

What is the difference between intravascular and extravascular haemolysis?

Answer 8

In extravacular haemolysis red cell content (hemoglobin and iron) are largely recycled.

In intravascular haemolysis, haemoglobin and iron are sent to the kidney and are then excreted in the urine.

Extravascular haemolysis forms unconjugated bilirubin from haem whereas intravascular does not. This bilirubin is sent to the liver for processing, failure of the liver to process this bilirubin leads to jaundice

Hence extravascular pathway cause jaundice and intravascular does not

*NB to note: the clinical and laboratory features of these 2 differs as well.

Question 9

What are the 2 diagnostic features of haemolysis?

Answer 9

• clinical features
• laboratory features

Question 10

What are the clinical features of intravascular haemolysis?

Answer 10

1. Anaemia
   -Iron deficiency
   -Smoky urine (hemoglobinuria)- present with pink or dark urine
   -enlarged spleen
   -Bony abnormalities
   -Leg ulcers
2. Zn deficiency
3. Megaloblastic
   anaemia
4. A.R. Failure
5. Pulmonary Hypertension

Question 11

Laboratory tests indicative of
Intravascular haemolysis

Answer 11

A. Coombs test
1. Release of haemoglobin into plasma:
*↓ Haptoglobin
*Plasma Hb
2. Renal clearance of haemoglobin:
*Haemoglobinuria
*Haemosiderinuria
3. Release of red cell enzymes
*↑ LDH

Question 12

What are the clinical conditions seen with predominant
Intravascular haemolysis?

Answer 12

• Paroxysmal Nocturnal Haemoglobinuria (PNH)
• Immediate blood transfusion reaction (I-BTR)
• Cold auto immune haemolytic anaemia (C-AIHA)
• Fragmentation haemolysis anaemia
• Malaria
• Sickle cell disease (SCD)

Question 13

What are the clinical features of extravascular haemolysis?

Answer 13

1. Anaemia
   -Enlarged spleen
   -Bony abnormalities
   -Leg ulcers
2. Jaundice
3. Gall stones
4. Fe overload
5. Megaloblastic
   anaemia
   (6. Pulmonary hypertension)

Question 14

Clinical conditions seen with predominant extravascular haemolysis

Answer 14

• Hereditary spherocytosis (HS)
• β-thalassaemia major
• HbH disease
• Warm auto-immune haemolytic anaemia (AIHA)
• Delayed blood transfusion reaction (D-BTR)

Question 15

Chronic haemolysis is one of the clinical features of EV and IV haemolysis. What are the specific features of chronic haemolysis?

Answer 15

• Iron overload (EVH)___excess Fe comes from the 1.GUT absorption of iron and from 2. chronic Red cell transfusion
• Iron deficiency (I.V.)____Fe lost with haemoglobin in the urine
• Splenomegaly (E.V. & I.V.)____1.Result from hypertrophy of macrophages clearing dead/lysed RBCs in the spleen. 2. Result from extramedullary haemopoiesis- blood cell synthesis outside the bone marrow; where spleen makes RBCs other than the bone marrow. * occurs when hemolysis occurred in early childhood.
• Skeletal abnormalities (E.V. & I.V.)- From expansion of the bone marrow in children. Lead to facial deformities: chipmunk face, frontal bossing, due to bone hypertrophy
• Gall bladder disease (E.V.)___Result from excess conjugated bilirubin in the gall bladder which cause pigment gall stones, causing pain in the right upper quadrant. And might cause obstructive jaundice if there is obstruction of bile flow in the bile duct.
• Folic acid deficiency (E.V. & I.V.)____RBCs are rich in folic acid. Their deficiency due to haemolysis reduces folic acid levels and tht leads to megaloblastic anaemia. Folate
  supplementation is recommended for chronic haemolytic states
• Aplastic crisis (E.V. & I.V.)___acute marrow hypoplasia
  affecting mainly erythropoiesis. (a decline in erythrocyte production) dues to Parvovirus type B19, which gains entry into red cell progenitors and
  destroys them.
• Pulmonary hypertension (I.V.)___Results from a depletion of nitric oxide (NO) due to Hb binding to NO and dragging NO to urine with it. Note tht NO has vasodilatory effect on the
  pulmonary vessels.

Question 16

Laboratory tests-extravascular haemolysis

Answer 16

COOMBS test
* ↑ Unconjugated bilirubin
(acholuric jaundice)
* ↑ LDH
* ↓ Serum haptoglobin

Question 17

What are the 3 causes of haemolysis?

Answer 17

1. Extra-corpuscular causes
2. Corpuscular causes due to membrane damage or defects
3. Intra-corpuscular causes

Question 18

What are the 3 Extra-corpuscular causes of haemolysis?

Answer 18

1. Macroangiopathic haemolysis:
   -occurs in large blood vessels
   -RBC membranes are damaged by turbulence and abrasion, colliding with each other n vascular walls in areas of high pressure, contributing to haemolysis.
   -Common in the heart; due to a valve that is abnormal, calcified or replaced with an artificial valve
   -Fragmentation lead to a reduction in the MCV, but the MCHC is usually normal.

*MCV- Mean Corpuscular Volume: measure of the average volume of a red blood cell
*MCHC: Mean Corpuscular Hemoglobin Concentration- (MCHC) remain normal because the amount of hemoglobin within the red blood cells doesn’t change. Even though the cells are smaller and fragmented, conc of hemoglobin within them stays relatively constant, keeping the MCHC within the normal range.

2. Microangiopathic haemolysis:
   -Occur in small vessels
   -fairly common, and is associated with severe and life-threatening diseases.
   -It occurs when:
   a).arteriolar vessels become narrow and rigid (e.g. renal
   disease involving glomeruli)
   b).Fibrin strands become deposited in the microvasculature and the red cells are mechanically damaged
   -Platelet count is often decreased due to platelet consumption during microthrombi formation.
3. March haemoglobinuria:
   -From Forceful contact of part of the body with a hard surface eg. sjambok injury may burst the
   red cells in the skin vessels.
   -If repeated, this may cause sufficient INTRAVASCULAR destruction of red cells to lead to haemoglobinuria.

Question 19

What are the 3 Intra-corpuscular causes of haemolysis

Answer 19

1. Heinz body haemolysis:
   -Refers to a process where red blood cells develop abnormal inclusions called Heinz bodies, which ultimately lead to their destruction (hemolysis).
   -Heinz bodies are aggregates of denatured hemoglobin that form within RBCs due to exposure to certain oxidative agents or toxins (reactive oxygen molecules).
   -It’s an example of combined INTRAVASCULAR and EXTRAVASCULAR haemolysis
   -RBC has a number of mechanisms to mop up any reactive oxygen molecules and render them harmless:
   a).It uses NADPH, produced by the pentose phosphate pathway, b).and glutathione, to scavenge the O2 ̄ and convert it to water.
   -Two basic mechanisms can lead to the overproduction of oxygen free radicals:
   (i)if the enzymes in the pathways responsible for scavenging the free radicals are deficient
   (ii)excessive amounts of oxidant are introduced into the cells
   Causes of Heinz body haemolysis:
   -Glucose-6-phosphate dehydrogenase (G-6-PD) deficiency
   -(RBCs) with bite deformity, also known as “bite cells,” are a characteristic feature observed in a condition called G6PD deficiency.
   *G6PD plays a crucial role in protecting the cells from oxidative stress.
2. Haemoglobin abnormalities (Haemoglobinopathies)
   -Worldwide, abnormalities of haemoglobin other than the unstable haemoglobins are a major source of morbidity and mortality.
   -They include the thalassaemias and sickle cell disease which can be lethal, as well as haemoglobins C, D and E.
3. Parasitic infestation
   -The haemolysis is both INTRAVASCULAR and EXTRAVASCULAR.
   -It is caused both by the malaria parasite breaking out of the red cell in which it has been
   growing, and by removal of infected red cells by the spleen.

Question 20

What are the corpuscular causes of haemolysis?

Answer 20

1. Hereditary spherocytosis (HS) and other inherited disorders of the red cell membrane and its skeleton
   -The red cell membrane skeleton is made primarily of a meshwork of a protein called spectrin.
   -Various other proteins bind to the spectrins, and also attach
   the skeleton to the phospholipid layer of the membrane.
   -In HS, the spectrin abnormalities or deficiencies lead to instability of the membrane with resultant loss of the typical biconcave
   conformation and the red cell assumes a spherical shape.
   -As the red cell
   passes through the spleen, more and more membrane is shed, and the spherocytes become smaller i.e. microspherocytes.
   -The microspherocytes are
   fragile and are eventually taken up by the macrophages of the spleen where
   they undergo EXTRAVASCULAR HAEMOLYSIS
2. Immune mediated haemolysis
   a).Autoimmune haemolysis
   -Production of antibodies towards an individual’s own red cells leads to destruction of the
   cell by damage to the membrane or phagocytosis by macrophages.
   Two types:
   (i).AI haemolysis due to IgG antibodies- warm antibody
   (i).AI haemolysis due to IgM antibodies-cold antibody
3. Toxins and venoms

a).Clostridial sepsis
-Clostridium perfringen is noted for its ability to produce profound, life-threatening haemolysis.
-This is due to the combination of phospholipase C acting on the lipid bilayer and proteolytic exotoxins digesting membrane proteins like spectrin leading to formation of spherocytes.
-Leptospirosis, certain snake venoms and some spider bites also contain enzymes which break down the red cell membrane.
b).Heavy metals
Arsine (AsH3), lead, copper and mercury can cause damage to the red cell membrane
c).Burns
-Direct thermal damage to red cells causes spectrin denaturation
-This results in gross disorganisation of the cytoskeleton and the formation of spherocytes.
-These cells may be lysed in the circulation or removed by the spleen. Third degree burns involving 15 – 20% or more of the body surface may result in severe haemolysis