ERYTHROCYTE (RBC) DISORDERS: POLYCYTHAEMIA AND ANAEMIA

Haematology

OVERVIEW

1. Polycythaemia (erythrocytosis)

2. Anaemia

-Regenerative: blood-loss or haemolytic

-Non-regenerative: primary or secondary bone

marrow disorder

1.POLYCYTHAEMIA/ERYTHROCYTOSIS

DEFINITION AND TYPES

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

-Relative • Dehydration (eg. increased water loss: e.g. vomiting,

diarrhoea, polyuric disorders) causing an apparent increase in RBC due to a decrease in fluid in circulation.

• Exercise, fear, excitement (eg. in the horse) causingadrenaline secretion, splenic contraction and transientredistribution of RBC from the spleen to the circulation.

-Absolute (real increase in RBCs)

• Secondary:

- chronic tissue hypoxia: heart/lung diseases, high altitude

- renal tumor or cysts increasing erythropietin (EPO) secretion

• Primary:

- polycythaemia vera (rare myeloproliferative disorder of RBC

precursors)

DEFINITION AND TYPES

CLINICAL IMPLICATIONS

-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

LABORATORY DIAGNOSIS OF DIFFERENT CAUSES

-Relative

• Dehydration: total protein and albumin

-Absolute

• Secondary to chronic hypoxia: arterial pO2

• Renal tumours or cysts (or others): erythropoietin EPO*)

• Polycythaemia vera: EPO

2. ANAEMIA

TYPES OF ANAEMIA

Anaemia

regenerative

nonregenerative

haemolytic

haemorrhagic

secondary B-M disorders

primary B-M disorders

ANAEMIA

A decrease in PCV, Hb concentration and/or RBC count

Low PCV

ANAEMIA: CLINICAL IMPLICATIONS

- Inadequate tissue oxygenation • pale mucous membranes

• weakness, inappetance, anorexia • syncope

- Compensatory mechanisms • tachypnoea (particularly if forced to exercise) • tachycardia, small and strong pulse

-Signs which may be associated with cause of anaemia • icterus • bleeding (petechiae,ecchymoses, melena, haematuria, haematomas)

• fever • splenomegaly

ANAEMIA: CLINICAL IMPLICATIONS

TYPES OF ANAEMIA

Anaemia

regenerative

nonregenerative

haemolytic

haemorrhagic

secondary BM disorders

primary B-M disorders

REGENERATIVE ANAEMIA

Characterized by an increase in the number of

RETICULOCYTES produced by the bone marrow to

compensate for the anaemia.

SIGNS OF REGENERATIVE ANAEMIA Reticulocytosis will produce:- MCV and RDW, MCH and MCHC- In blood smears with Romanowsky stains: • polychromasia • anisocytosis

TYPES OF ANAEMIA

Anaemia

regenerative

nonregenerative

haemolytic

haemorrhagic

secondary BMdisorders

primary B-M disorders

HAEMORRHAGIC ANAEMIA

Plasma total protein generally (because protein is lost together with RBC)

Plasma clear

-ACUTE BLOOD LOSS

Reticulocyte response will only be detected in blood

after 3-4 days !!

Causes:

• Trauma, surgery

• Coagulation disorders

• Others

HAEMORRHAGIC (blood-loss) ANAEMIA

- External. Causes:• Gastrointestinal ulceration and tumours • Parasitism

-normo to microcytosis-hypochromasia- ↑ platelet count-reticulocytes can decrease

CHRONIC BLOOD LOSS

- Internal : blood loss into abdomen/chest

In many cases signs of RBC regeneration are present in blood but progressive depletion of iron stores mayproduce IRON DEFIENCY ANAEMIA with:

IRON DEFICIENCY ANAEMIA

TYPES OF ANAEMIA

Anaemia

regenerative

nonregenerative

haemolytic

haemorrhagic

secondary B-M disorders

primary B-M disorders

HAEMOLYTIC ANAEMIA

Plasma total protein within reference range or Plasma can be icteric or hemolysed

Abnormal erythrocyte morphology (Heinz bodies, RBC parasites, spherocytes) may suggest a haemolytic cause for

the anaemia

IN REGENERATIVE ANAEMIAS:TPP and plasma colour can be used to differentiate haemolysis and haemorrhage

Haemorrhagic anaemia Haemolytic anaemia

TPP < 60 g/L

PLASMA CLEAR

TPP > 60 g/L

PLASMA ICTERIC/

HEMOLYSED

HAEMOLYTIC ANAEMIA

Clinical signs associated with an increase in haemoglobincatabolism: • Haemoglobinemia and haemoglobinuria • Icterus

Icteric serum when serum bilirubin levels >20mol/L

Icteric tissues when serum bilirubin levels >50mol/L

HAEMOLYTIC ANAEMIA

Red blood cell lysis may occur by two mechanisms:

1. INTRAVASCULAR HAEMOLYSIS

2. EXTRAVASCULAR HAEMOLYSIS

INTRAVASCULAR HAEMOLYSIS (causes)

-Parasites/infectious causes

-Vascular Endothelial Lesions

-Oxidant damage

- Others

INTRAVASCULAR HAEMOLYSIS (laboratory findings)

- Parasites/infectious causes: Blood smears, Serology/PCR

-Vascular Endothelial Lesions: Schistocytes in blood smears

- Oxidant damage: Heinz bodies in blood smears

In addition to PCV,TPP within the reference range or

and icteric/hemolysed plasma

Heinz bodies

Schistocyte

EXTRAVASCULAR HAEMOLYSIS

-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

- INMUNE-MEDIATED HAEMOLYTIC ANAEMIA

INMUNE-MEDIATED HAEMOLYTIC ANAEMIA

- Idiopathic (unknown mechanisms) - Secondary to: • Infectious agents • Drugs/insecticides/vaccines/neonatal isoerythrolysis

CAUSE THE APPEARANCE OF ABNORMAL ANTIGENS ON THE ERYTHROCYTE

CELL MEMBRANE

INMUNE-MEDIATED HAEMOLYTIC ANAEMIA (laboratory findings)

In addition to PCV, TPP = within the reference range or

and yellow coloured plasma

Spherocytosis (canine blood)Autoagglutination

Gross autoagglutination on a slide

Spherocytosis Autoagglutination

ADDITIONAL TESTS TO CHARACTERIZEINMUNE-MEDIATED HAEMOLYTIC ANAEMIA:

-COOMBS TEST

- ERYTHROCYTE FRAGILITY TEST

COOMBS TEST

Detects antibodies directed at the erythrocyte membrane

Falses +´s: -some chronic infections - “ parasites (heartworms, haemobartonella) - “ drugs (trimethoprim-sulfa) - “ neoplasms

Falses -´s: in some cases of inadequate antibody production

The test is species-specific

Whole blood in a hypotonic solution (0.55% NaCl)

Normal RBCs absorb water from the hypotonic solution for osmotic equilibrium and are distended but not haemolyzed

Membranes of fragile RBCs (spherocytes, and those with enzyme deficiencies or damaged by some drugs) cannot withstand distension and are haemolyzed

ERYTHROCYTE FRAGILITY TEST:BASIS

TYPES OF ANAEMIA

Anaemia

regenerative

nonregenerative

haemolytic

haemorrhagic

secondary B-M disorders

primary B-M disorders

NON-REGENERATIVE ANAEMIA

Characterized by an absence of, or reduction in reticulocyte response in an anaemic animal.

This will produce:

• Normocytic-normochromic anaemia MCV and RDW, MCH and MCHC within the reference ranges

• In blood smears with Romanowsky stains: - absence of polychromasia and anisocytosis

NON REGENERATIVE ANAEMIA (causes)

- Primary bone marrow disorders:• some myeloproliferative, lymphoproliferative and

myelodisplastic disorders

• virus (feline leukaemia/ canine parvovirus)

• some drugs: oestrogens, inmunosuppressive agents,

non-steroid anti-inflammatories

- Secondary: •chronic inflammatory disease, some endocrine diseases

•chronic renal failure with decreased erythropoietin levels

NON REGENERATIVE ANAEMIA (laboratory findings)

- Primary (bone marrow disorders): Diagnosis by bone marrow evaluation + specific tests. Leukopenia and/or thrombocytopenia may also occur

- Secondary: Laboratory findings of the primary disease. (e.g. chronic renal failure: BUN and creatinine)

In addition to PCV and absent/reduced signs of RBC regeneration (reticulocytes)

NON REGENERATIVE BLOOD SMEARS MAY BE SEEN IN HAEMORRHAGE OR

HAEMOLYSIS IF:

- RBC loss or destruction has occurred within the previous 4

days

- chronic haemorrhage has induced iron deficiency anaemia

- animals with a low reticulocyte response: bovine, and

particularly equine species. In the latter, the only sign that

regeneration is occurring may be a small increase in MCV.

CLASSIFICATION OF ANAEMIASBASED ON RBC INDICES

- Macrocytic-hypochromic (regenerative) - Normocytic-normochromic (non regenerative) - Microcytic-hypochromic or normochromic (iron deficiency)

DIAGNOSIS OF ANAEMIAS: SUGGESTED APPROACH

The following questions must be addressed:

1. Regenerative or non-regenerative?

2. If regenerative: haemolytic or haemorrhagic?

3. If non-regenerative: primary or secondary bone

marrow disorder?