Haemolysis

Question 1

Breakdown products of Hb?

Answer 1

Bilirubin - JAUNDICE

Question 2

Define haemolysis?

Answer 2

Premature red cell destruction, i.e: shortened red cell survival (<120 days)

Question 3

Why are red cell particularly susceptible to damage?

Answer 3

1. Have a biconcave shape to transit the circulation effectively
2. Have limited metabolic reserve and rely exclusively on glucose metabolism for energy (no mitochondria)
3. Cannot generate new proteins once in the circulation, if damaged (no nucleus)

Question 4

What is compensated haemolysis?

Answer 4

These patients do not become anaemic (Hb maintained)

Increased red cell destruction is compensated by increased red cell production

Question 5

What is decompensted haemolysis?

Answer 5

AKA haemolytic anaemia

Increased rate of red cell destruction, exceeding the bone marrow’s capacity for red cell production (Hb falls)

Question 6

Consequences of haemolysis?

Answer 6

Erythroid hyperplasia - increased bone marrow red cell production (check reticulocyte count)

Excess red cell breakdown production, e.g: bilirubin
NOTE - clinical features different by aetiology and site of red cell breakdown

Question 7

Issues assoc. with investigating haemolysis?

Answer 7

No possible to directly measure red survival routinely

It relies on detecting the consequences of haemolysis and then investigating the cause:
• Increased red cell production
• Detection of breakdown production (specific products or pattern help determine the cause)

Question 8

Bone marrow response to haemolysis?

Answer 8

1. Reticulocytosis - request a reticulocyte count if haemolysis if suspected
2. Erythroid hyperplasia - bone marrow is not routinely done

If anaemia occurs, Epo production increases

Question 9

Do reticulocytes have a nucleus?

Answer 9

No

Question 10

Appearance of a blood film in a patient with haemolysis?

Answer 10

Polychromasia (due to reticulocytosis)

Can use methylene blue stain for ribosomal RNA; now, automated reticulocyte counting is used

NOTE - reticulocytosis are not diagnostic of haemolysis; also, occurs in response to bleeding, iron therapy in iron deficiency anaemia

Question 11

Classifying haemolysis according to site of destruction?

Answer 11

Extravascular (more common) vs intravascular (rare)

This refers to the site of haemolysis

NOTE - different mechanisms therefore therefor result in the detection of different breakdown products

Question 12

Where does extravascular haemolysis occur?

Answer 12

Takes place out with the bloodstream; cells are taken up by RES (spleen and liver) and destroyed there

Question 13

Where does intravascular haemolysis occur?

Answer 13

Red cells destroyed within circulation

Dangerous and life-threatening, as intracellular products are not held safely within a cell

Question 14

Clinical signs of extravascular red cell destruction?

Answer 14

Hyperplasia at the site of destruction (splenomegaly +/- hepatomegaly)

Release of protoporphyrin:
• Unconjugated bilirubinaemia (jaundice and, chronically, gallstones)
• Urobilinogenuria

NOTE - these are NORMAL PRODUCTS IN EXCESS

Question 15

Clinical signs of intravascular red cell destruction?

Answer 15

1. Haemoglobinaemia (free Hb in circulation)
2. Methaemalbuminaemia - Hb binds to albumin
3. Haemoglobinuria - urine is pink initially but, if left standing, turns black; may be mistaken for haematuria but there are no rbcs in the urine, just Hb
4. Haemosiderinuria - excess iron excreted in the urine

NOTE - these are all ABNORMAL PRODUCTS

Question 16

Why is intravascular haemolysis life-threatening?

Answer 16

Abnormal, toxic products in the bloodstream

Question 17

Causes of intravascular haemolysis?

Answer 17

ABO incompatible

G6PD deficiency - enzyme deficiency

Severe falciparum malaria (AKA Blackwater Fever; as the urine sits, it turns black)

Even rarer:
• Paroxysmal Nocturnal Haemoglobinuria (PNH)
• Paroxysmal Cold Haemoglobinuria (PCH)

Question 18

Causes of extravascular haemolysis?

Answer 18

Essentially all other causes of haemolysis

Question 19

Ix for haemolysis?

Answer 19

1. Confirm haemolytic state:
   • FBC + BLOOD FILM
   • Reticulocyte count (assess bone marrow response)
   • Serum unconjugated bilirubin
   • Serum haptoglobins (if low, sensitive for haemolysis)
   • Urinary urobilinogen
   NOTE - haemolysis may not be anaemic
2. Identify cause:
   • History and examination - genetic (chronic) or acquired
   • Blood film
   • Specialist investigations (Direct Coombs’ test and others)

Question 20

Signs that may be seen on blood film?

Answer 20

Membrane damage - spherocytes, e.g: autoimmune haemolytic anaemia; also seen in congenital/hereditary spherocytosis

Mechanical damage - red cell fragments

Oxidative damage - Heinz bodies

Others, e.g: Hbs (Sickle cells)

Question 21

Classifying haemolysis according to side of red cell defect?

Answer 21

1. Premature destruction or normal red cells (immune or mechanical damage)

Abnormal red cells:
2. Abnormal cell membrane
3 Abnormal red cell metabolism
4. Abnormal Hb

NOTE - can be congenital or acquired

Question 22

Immune causes of premature red cell destruction?

Answer 22

Acquired:
• Autoimmune haemolysis - patient’s own antibodies are destroying red cells
• Alloimmune haemolysis - foreign antibodies are destroying red cells

Question 23

Types of auto-antibody and causes of autoimmune haemolysis?

Answer 23

IgG (warm) - more common than IgM:
• Idiopathic - by far, the most common cause
• Autoimmune disorders, e.g: SLE
• Lymphoproliferative disorders, e.g: CLL
• Drugs, e.g: high-dose penicillin
• Infections

IgM (cold):
• Idiopathic
• Infections, e.g: EBV, mycoplasma
• Lymphoproliferative disorders

Question 24

Explain the direct Coomb’s test (DAT)

Answer 24

Identifies antibody (and complement) bound to patient’s own RBCs

Patient’s blood sample will contain RBCs coated with IgG-complement

A mouse anti-human IgG antibody is added to the blood sample and agglutination occurs

Question 25

Causes of alloimmune haemolysis?

Answer 25

``` Immune response (production of Ab) - as in haemolytic transfusion reactions: • IMMEDIATE (IgM) - predominantly INTRAVASCULAR haemolysis • DELAYED (IgG) - predominantly EXTRAVASCULAR haemolysis (less serious) ``` Passive transfer of Ab - as in haemolytic disease of the newborn: • Rh D • ABO incompatibility • Others, e.g: anti-Kell

Question 26

Mechanical causes of premature destruction of normal RBCs?

Answer 26

Acquired causes of mechanical red cell haemolysis: • DIC - shearing of RBCs in circulation • Haemolytic uraemic syndrome, e.g: E.coli O157 • TTP (thrombotic thrombocytopaenia purpura) - linked to haemolytic uraemic syndrome • Leaking heart valve - causes a microangiopathic haemolytic anaemia (MAHA), leading to RBC fragmentation due to mechanical damage • Infections, e.g: malaria

Question 27

Describe appearance of a burns related haemolysis

Answer 27

Microspherocytes (small, spherical RBCs) Red cells are sheared as they pass through damaged capillaries, i.e: this is only seen in severe burns

Question 28

Acquired causes of RBC membrane defects?

Answer 28

All are very rare: • Liver disease (Zieve's syndrome) • Vitamin E deficiency • Paroxysmal nocturnal haemoglobinuria - lots of iron and Hb in urine

Question 29

How does Zieve's syndrome occur?

Answer 29

Haemolysis, alcoholic liver disease, hyperlipidaemia (changes in lipids due to liver disease)

Question 30

Congenital causes of RBC membrane defects?

Answer 30

Hereditary spherocytosis (most common) - autosomal dominant NOTE - even within families, it shows a variable clinical course, with some presenting in childhood with severe symptoms and others not presenting until adulthood

Question 31

Explain what happens in hereditary spherocytosis

Answer 31

Red cell membrane is abnormal and has reduced deformability (not bi-concave anymore) Increased transit time through spleen (splenomegaly and haemolysis); oxidant environment in the spleen causes chronic extravascular haemolysis Often, patients compensate (increased RBC production) until they have an intercurrent infection, when they develop a severe anaemia

Question 32

Key features of red cell metabolism?

Answer 32

Red cells are dependent on glucose metabolism (glycolysis) for ATP generation AND On the G6PD dehydrogenase pathway, for anti-oxidant generation to protect the red cell against oxidative damage

Question 33

Congenital causes of abnormal red cell metabolism?

Answer 33

G6PD deficiency - failure to cope with oxidative stress Failure of metabolic processes, e.g: pyruvate kinase deficiency - leads to a failure to generate ATP NOTE - often appear on exposure to certain drugs that cause oxidative damage, e.g: dapsone, salazopyrin; even normal RBCs will be damaged by sufficient oxidative stress

Question 34

Congenital causes of abnormal Hb (haemglobinopathies)?

Answer 34

Sickling disorders - HbS polymerises and this leads to shortened RBC survival NOTE - caused by a point mutation in beta globin chain

Question 35

Types of sickling disorders?

Answer 35

Trait - asymptomatic carrier state Sickle cell anaemia Sickle cell disease NOTE - variable clinical severity

Question 36

Young boy presents: • Facial features indicate frontal bossing - due to increased production of blood cells, there is splenomegaly, marrow expansion (inc. in skull) • X-ray shows hair-on-end appearance Blood film shows a hypochromic, microcytic anaemia; there are also nucleated red cells and target cells present Bone marrow biopsy shows lots of nucleated red cells (due to erythroid hyperplasia)

Answer 36

Beta thalassaemia major

Question 37

RhD -ve man who had iron deficiency anaemia received a unit of RhD +ve blood; 10 days later, he became jaundiced and anaemic Explain what has happened

Answer 37

Delayed haemolytic transfusion reaction, as it occurred 10 days later He developed an alloantibody to RhD +ve RBCs that were transfuse (IgG so the reaction was delayed and caused extravascular haemolysis) NOTE - IgM responsible for immediate reaction and intravascular haemolysis

Question 38

28 year old female presents with: • Splenomegaly • Intermittent mild jaundice • Gallstones Father had a splenectomy in young adulthood, for gallstones

Answer 38

Hereditary spherocytosis Blood film shows small RBCs with a loss of central pallor

Question 39

German man with longstanding haemolysis Blood film shows no spherocytes

Answer 39

HbKoln - rare Hb variant identified in Germany NOTE - individuals with Hb variants are at risk of haemolysis; he has splenomegaly due to chronic haemolysis leading to hyperplasia of the spleen

Question 40

Thai girl with anaemia her Hb is 80-100 Supravital stain of blood film shows HbH in cells She has intermittent jaundice when she is unwell, has a fever and is exposed to oxidant drugs

Answer 40

HbH disease - only one alpha gene left, so accumulating beta chains form HbH (a beta4 tetramer), which is precipitated by oxidative stress (unwell) There is haemolysis and shortened RBC survival

Question 41

2 babies both have anaemia and are jaundiced One is DCT -ve and the other is DCT +ve Why do both have haemolytic disease of the newborn?

Answer 41

Different mechanisms of haemolytic disease of the newborn DCT -ve baby - due to ABO incompatible DCT +ve baby - due to RhD +ve Both cause shortened RBC survival, increased haemolysis

Question 42

Boy with G6PD deficiency has had a splenectomy Blood film has a special stain

Answer 42

Heinz bodies are shown using the preparation Heinz bodies - red cell inclusions comprised of denatured Hb, which would normally be removed by the spleen; they are seen in G6PD deficiency and unstable Hb, e.g: HbH If spleen was still intact, HbH would have been removed from the cells, leading to the appearance of 'bite' cells (AKA degmacyte)