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Pathology of Haematopoietic and Lymphoid Systems > (W1) Erythrocyte Disorders > Flashcards

(W1) Erythrocyte Disorders Flashcards

1
Q

What blood cells are found in mammals (and those found in birds, reptiles and fish)?

A

Mammals - RBCs, WBCs and platelets

Exotics - nucleated RBCs, heterophils and thrombocytes (nucleated)

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2
Q

What promotes erythropoiesis?

A

Main one - Erythropoietin (EPO)

Others - IL-3 and colony stimulating factor

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3
Q

What stimulates EPO? What inhibits EPO?

A

Stimulates - androgens

Inhibits - corticosteroids and oestrogens

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4
Q

What is the relationship between age and red blood cell counts and why is this relevant?

A

RBCs are low after birth and increase to adult levels within a few months

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5
Q

Describe the maturation of red blood cells (also what are the last 3 stages called?)

A
  • Immature: larger nuclei (protein synthetic machinery) and dark blue cytoplasm (RNA and ribosomes for translation)
  • As cells divide: nucleus becomes smaller and more pyknotic/nucleus is eventually expelled as it is obsolete
  • Mature RBC: has nor organelles or nuclei (so can’t synthesise proteins) and contains large amounts of Hb

Last 3 stages

  • metarubricyte (last stage of maturation that contains nucleus)
  • reticulocyte
  • mature erythrocyte
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6
Q

How do you differentiate between reticulocytes with Romanowski-type stains (e.g. Wright Giemsa) and New Methylene Blue stain?

A

Mature RBC:

  • Romanowski stain; will stain red with a central pallor
  • New methylene blue; will stain blue-green

Reticulocyte:

  • Romanowski; will stain purple-blue (lavender blue colour), are larger than mature RBCs, and are called polychromatophils
  • New Methylene Blue; will appear as a blue disk (blue stained cytoplasm) with blue granular structures within it (this is RNA, (poly)ribosomes and mitochondria) - called reticulocytes
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7
Q

What is anaemia characterized by on a haematology analyser?

A
  • Low RBC, Hb and/or HCT (or PCV)

- Look at erythrocyte indices (MCV, MCH, MCHC, RDW)

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8
Q

What colour change do RBCs undergo as they mature?

A

blue to orange due to the increased concentration of Hb in the cytoplasm as they mature

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9
Q

What are the 3 main causes of anaemia?

A
  • Blood loss
  • Haemolysis (destruction of erythrocytes)
  • Reduced bone marrow production
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10
Q

What are the two types of anaemia and what are the causes of both?

A

Regenerative - haemorrhage or haemolysis

Non-regenerative - primary (problem in the bone marrow) and secondary (problem that affects the BM, not in the BM) bone marrow disorders

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11
Q

How can we identify regenerative anaemia? How does this present on a blood smear (summary version)?

A

There will be an increased production and release of reticulocytes in the peripheral blood (not in equines!!)

  • Increased MCV and RDW
  • Decreased MCH and MCHC
  • Polychromasia (the presence of polychromatophils in increased numbers) and anisocytosis (uneven RBC sizes - size variation)
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12
Q

How does regenerative anaemia present itself on a blood smear?

A

1) Immature anucleate erythrocytes that are:
- larger
- have a larger central pallor than a mature RBC (due to lower cytoplasmic Hb)
- purple-blue in colour
These are polychromatophils (will see polychromasia on blood smear)

2) Due to increased numbers of reticulocytes that are larger than mature RBCs, there will be a greater degree of size variation (anisocytosis) in the blood smear

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13
Q

What are the definitions of MCV, MCH/MCHC and RDW (units and equations also)?

A

MCV (Mean Cell Volume) - the average volume of the average erythrocyte (femtolitres fL)
MCV = (PCV x 10)/ RBC count (millions)

MCH (Mean Corpuscular Haemoglobin)

MCHC (Mean Corpuscular Haemoglobin Concentration) - the average Hb concentration in the average erythrocyte (grams of haemoglobin per dL of erythrocytes)
MCHC (g/dL) = Hb concentration (pg)×100]÷ Hct (%)

MCHC more accurate than MCH as its calculation doesn’t require RBC count

RDW (Red Cell Distribution Width) - an index of the degree of anisocytosis
RDW = (standard deviation of MCV / MCV) × 100

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14
Q

When are you able to detect the reticulocytosis (bone marrow erythroid response)?

A

48hrs to 72hrs after occurrence of anaemia (provided that enough time has elapsed for increased reticulocyte release)

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15
Q

What are the 2 types of reticulocytes (in cats and dogs)?

A
  • Aggregate reticulocytes: similar to those in other species and (dogs contain 1% aggregate)
  • Punctate reticulocytes: contain smaller, blue-stained dots

Aggregate more in dogs but both types are present in cats

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16
Q

What is the degree of reticulocytosis in different species?

A

most pronounced in dogs , then cats then ruminants

Ruminants don’t have reticulocytes in their blood in health due to their long life span (they increase modestly with anaemia regeneration)

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17
Q

How is anaemia regeneration identified in equines? How does this appear on a blood smear (relate to indices) and what can you do in clinical practice to detect regeneration?

A

They release increased numbers of macrocytes (large erythrocytes) into their peripheral blood (called macrocytosis)

  • Blood smear: anisocytosis
  • Indices: increased MCV and RDW
  • can do serial measure meats of PCV; should measure an increase
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18
Q

What are the clinical consequences of anaemia?

A
  • Pale mucous membranes
  • anorexia, weakness and inappetence

Compensatory mechanisms:

  • tachycardia
  • tachypnoea (rapid breathing)
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19
Q

What are the causes of Haemorrhagic Anaemia?

A
  • Blood vessels damaged due to trauma, neoplasia, ulceration, etc
  • Acquired or congenital coagulation factor deficiencies or von Willebrand disease
  • Thrombocytopenia (marked)
  • Parasitism; whip/hookworms (dogs), haemonchosis and ostertagiasis (ruminants), coccidiosis, ticks and bloodsucking lice/fleas (dogs, cats and calves)
  • Removal of blood for transfusion
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20
Q

Explain the erythrocyte kinetics in acute external blood loss

A
  • After whole blood is lost, blood volume decreases but Hct and [total protein] stays the same (as RBCs and plasma are lost proportionately)
  • Thirst results from hypovolemia to replenish ECF volume
  • Hypovolemia induces movement of ECF into the intravascular space (from extravascular space), which expands the blood volume
  • This shift of fluid dilutes the erythrocytes (and plasma proteins), which causes anaemia (and hypoproteinaemia)

External blood loss leads to iron deficiency

21
Q

What does the degree of haemorrhagic anaemia depend on?

A
  • the quantity and duration of haemorrhage
  • the time period from the onset of haemorrhage

splenic contraction will decrease the severity of anaemia as splenic blood is rich in erythrocytes (especially in dogs and horses)

22
Q

Internal blood loss (haemothorax and haemoabdomen)

A
  • severity of haemoperitoneum diminished by resorption (autotransfusion) of ~65% of erythrocytes within 2 days and 80% within 1-2 weeks
  • doesn’t cause iron depletion as erythrocytes are absorbed or destroyed (Fe is reutilized e.g. for production of Hb)
23
Q

What is iron deficiency anaemia mainly caused by and what would you see on a blood smear?

A

CHRONIC, LOW-GRADE, EXTERNAL BLOOD LOSS

  • gastrointestinal blood loss (e.g. tumours); bleeding into GI tract
  • urinary blood loss; persistent low-grade haematuria
  • parasitism; blood sucking parasites

RBC regeneration is present but progressive depletion of iron stores may produce iron deficiency anaemia

Blood Smear:

  • normo to microcytosis (decreased MCV)
  • hypochromasia (decreased MCH and MCHC)
  • increased platelet count
  • poikilocytosis (variable abnormalities of RBC shape OR variable shapes of erythrocytes)
24
Q

What is hypochromia and microcytosis?

What do they indicate?

A

Hypochromia - increased numbers of hypochromic erythrocytes (larger central pallor)

Microcytosis - presence of increased numbers of erythrocytes of smaller sizes

Both result from defective haemoglobin synthesis caused by iron deficiency

25
Q

What is poikilocytosis and what is the main cause of it?

A

variable shapes of erythrocytes

  • oxidation of membrane proteins
  • iron deficiency causes RBCs to become more fragile and less deformable (these changes decrease their lifespan)
26
Q

What is a schistocyte?

A
  • an abnormal shape that an erythrocyte can take

It is a fragment of an RBC

27
Q

What are the different names for abnormal RBC shapes?

A
  • Schistocyte
  • Acanthocyte
  • Ovalocyte
28
Q

What is haemolysis?

A

the lysis of RBCs

29
Q

What are the 2 mechanisms by which RBCs can be lysed?

A
  • Intravascular haemolysis (lysis occurs within the blood vessels
  • Extravascular haemolysis (destruction of RBC occurs in macrophages near venular sinuses of spleen, liver and BM)

Intra- and extravascular can occur together and disorders can switch from one to another

30
Q

What are the causes of intravascular haemolysis?

A
  • Parasitism; Babesia, Mycoplasma haemofelis, toxins ((Leptospira, Clostridium)
  • Vascular endothelial lesions; haemangiosarcoma, DIC, splenic torsion, heartworm disease
  • Oxidant damage; vegetable, animal toxins and drugs (onions, snake venom, methylene blue, acetaminophen/paracetamol)

Others: immune-mediated haemolytic anaemia, copper poisoning, severe hypophosphataemia*, Zn poisoning, genetic (pyruvate kinase/phosphofructokinase deficiency)

31
Q

What are the causes of extravascular haemolysis?

A

Physiological; (aged erythrocytes) removed by the macrophage-monocyte system in the spleen

Pathological; (Auto)antibodies are produced against “normal” erythrocytes that are phagocytosed by the spleen → Immune-mediated haemolytic anaemia (some cases - RBC may rupture within the vessels i.e. concurrent intravascular haemolysis)

32
Q

How is bilirubin produced and how does it move throughout the body?

A
  • 80% of bilirubin is produced from the degradation of haemoglobin from erythrocytes undergoing normal (removal of aged or effete cells) or abnormal destruction (intra- and extravascular haemolysis)
    1) RBC is phagocytosed and degraded by macrophage
    2) Hb is metabolised in macrophage and bilirubin is produced and released into blood plasma
    3) Unconjugated bilirubin enters liver hepatocytes and gets conjugated within the hepatocyte
    4) Conjugated bilirubin then enters the biliary system and then into the small intestine, where it will eventually be lost on the faeces
33
Q

How can you differentiate between haemorrhage and haemolysis (e.g. when looking at samples in a capillary tube)?

A
  • You look at the plasma colour and plasma total protein concentration

Haemorrhage:

  • plasma total protein may be low due to increased protein loss secondary to haemorrhage)
  • low PCV (visually)?
  • clear plasma

Haemolysis:

  • RBCs are lysed but there’s no loss of blood so low plasma protein IS NOT expected
  • Haemoglobinaemia and Haemolysed (pink/red) plasma; Hb released into plasma due to lysed RBCs
  • Icteric (yellow/orange) plasma; if hyperbilirubinaemia develops secondary to haemolysis
34
Q

What are the clinical signs associated with increased Hb catabolism?

A
  • Haemoglobinaemia and haemoglobinuria
  • Icterus (icteric serum bilirubin levels >20umol/L and icteric tissues when serum bilirubin levels >50umol/L)

Icterus can appear in mucous membranes, sclera and skin (in severe cases)

35
Q

What are the causes of Immune-Mediated Haemolytic Anaemia (IMHA)?

What is the mechanism?

A
  • primary/idiopathic (unknown cause)
  • secondary to: infectious agents, drugs/insecticides/vaccines/neonatal isoerythrolysis

Mechanism:
- appearance of abnormal erythrocyte cell membrane -> attacked by immune system (recognise RBCs as foreign so are lysed)

i.e. IgG on the surface of erythrocyte (recognised as foreign) -> Fc receptor on macrophages -> macrophage phagocytoses RBC

36
Q

What happens as a result of only a part of the RBC cell membrane being phagocytosed in IMHA?

A
  • RBCs become smaller and rounder than normal RBCs
  • Called spherocytes on blood smear examination
  • They lack central pallor, have dark/dense cytoplasm

It is hard to distinguish spherocytes from normal RBCs in cats and horse (in which their RBCs are lacking a central pallor)

37
Q

What is a major sign of immune-mediated haemolytic anaemia (IMHA) when looking at a blood sample?

A

Erythrocyte Auto-Agglutination

  • increased agglutination; strong agglutination may sometimes be visible macroscopically (would see specs of blood forming on the wall of a tube if you tilt it)
38
Q

What method can you use to detect increased agglutination in microscopic examination?

A
  • Mix equal amounts of EDTA blood and normal saline on a glass slide (to break up Rouleaux formations)

You don’t need to stain the slide but you can still see agglutination on stained slide

39
Q

What are Rouleaux formations and what species are they associated with?

A
  • where RBCs are stacked on top of each other to form column shapes (seen microscopically)

Typical in cats and horses

40
Q

What is non-regenerative anaemia characterized by?

A
  • The absence of reticulocyte response in an anaemic animal (provided that enough time has elapsed for increased reticulocyte release) (doesn’t apply to equines as don’t exhibit reticulocytosis!!)
41
Q

How will non-regenerative anaemia present on a blood smear and what will be the erythrocyte index changes (if any)?

A

Blood smear:
- absence of polychromasia and anisocytosis

  • Normocytic (normal MCV)
  • Normochromic (normal MCH and MCHC)
    All indices are within their normal reference ranges
42
Q

What are causes of non-regenerative anaemia? (FYI)

A

Primary BM disorders:

  • some myeloproliferative, lymphoproliferative and myelodysplastic disorders
  • viral infections (feline leukaemia virus/canine parvovirus)
  • some drugs e.g. oestrogens, immunosuppressive agents

Secondary BM Disorders:

  • Chronic/systemic/inflammatory disease, some endocrine diseases
  • Chronic renal failure with decreased erythropoietin levels
43
Q

What is erythrocytosis?

A

An increase in PCV, Hb concentration and/or RBC count

44
Q

What is relative erythrocytosis?

A

There is no increase in RBC production in the BM but due to the removal of fluid from the blood, PCV increases (as the relative proportion of RBCs increases)

45
Q

What are the causes of relative erythrocytosis?

What about greyhounds??

A

Dehydration:
- increased water loss from e.g. vomiting, diarrhoea, polyuric disorders causing apparent (relative) increase in RBC due to decreased fluid circulation

Exercise, Fear, Excitement:
- in horses causing adrenaline secretion, splenic contraction and transient distribution of RBC form the spleen to circulation

Greyhounds/sighthounds have higher erythrocyte mass (erythrocytosis) than other dog breeds

46
Q

What is absolute erythrocytosis?

A

The real increase in bone marrow RBC production

47
Q

What are the causes of absolute erythrocytosis?

A

Secondary:

  • chronic tissue hypoxia: heart/lungs diseases, high altitude
  • renal tumour or cysts increasing EPO secretion

Primary:
- polycythaemia vera (rare myeloproliferative disorder of RBC precursors)

48
Q

How are the 2 different types of erythrocytosis diagnosed in the lab?

A

Relative:
- Dehydration: increased total protein and albumin

Absolute:

  • secondary to chronic hypoxia: decreased arterial pO2
  • renal tumours or cysts (or others): increased EPO
  • polycythaemia vera: decreased EPO
49
Q

What are the clinical implications of erythrocytosis?

A
  • Cardiovascular signs due to blood hyperviscosity and peripheral hypoxia (increased pulse and respiratory rate)
  • Neurological signs (syncope, lethargy) due to poor brain perfusion,
    and bleeding tendencies

Hyperviscosity syndrome:

  • cardiovascular signs
  • neurological signs

Pathology of Haematopoietic and Lymphoid Systems (4 decks)

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