Anaemia

clinical presentation

» Lethargic or collapsed

» Pale mucus membranes

• Jaundiced?

» Tachycardia

» Bounding or weak peripheral pulses

» Hypotension

» Altered respiration?

severity of anaemia

» Depends on the species normal for Hct (hematocrit. It is the percentage of total blood volume made up of red blood cells (erythrocytes))/PCV (packed cell volume)

» Mild – may reflect other disease process, worth monitoring, but unlikely to be primary investigative focus

• Canine between lower reference interval (~37%) and 30% (may be differences for greyhounds/sighthounds)

• Feline below lower reference interval (~27%) and 20%

• Equine – depends on breed (Reference interval usually ~37-58% in ‘hotbloods’; ~32-46% warmbloods; ~24-44% in ‘coldbloods’ / native breeds

» Moderate- likely to be a primary concern, investigation may indicate the underlying disorder

• PCV below 20%

» Marked- significant clinical concern- requires investigation, and rapid initiation of treatmentsupportive if underlying cause is not yet known. Pathophysiology of the anaemia is likely the primary cause of illness, or a consequence of the primary cause.

• PCV below 12-15%

acute or chronic blood loss

Acute blood loss

» Blood is lost over a few hours

» Anaemia results from dilution of remaining erythrocytes

» Recovery

• Reabsorption of erythrocytes (if internal haemorrhage)

• Tissue hypoxia stimulates production of erythropoetin

Chronic blood loss

» Blood is lost over days or weeks or months

» If external loss then Fe deficiency biggest factor in development of anaemia

cytopenia-a lower-than-normal number of blood cells circulating in the body

haemorrhage = loss

haemolysis = destruction

anaemias

increased loss/decreased production anaemia

haemorrhage = loss

haemolysis = destruction

Increased Loss

» Predominantly regenerative

» Red cell morphology extremely helpful in

refining likely causes

» Red cell parameters may be useful in

determining possible underlying mechanisms

Decreased Production

» Non-regenerative

» Red cell morphology might provide clues, but

often may be unremarkable

anaemia

going a step further

anaemia- haemorrhage

Internal Haemorrhage

» Haemorrhage into cavities e.g.

• Thoracic

• Pericardial

• Peritoneal

• Joints

» Extravasated (a fluid, such as blood, lymph, or an intravenous medication, has leaked or been forced out of a blood vessel or natural channel into the surrounding tissue) blood is broken down and

recycled – iron is available for new red cell

production

» Regenerative

External Haemorrhage

» Haemorrhage outside the body e.g.

• External trauma

• Epistaxis -nose bleed

• Haematemesis - vomiting of blood - e.g. digestive blood like coffee granules, bleeding in intestine/stomach

• Haematuria - urinating with blood

• Melena - black tarry faeces - smelly

» Blood (and hence iron) is lost outside the body.

If rate of loss is in excess of the ability to absorb

iron from the diet

» —> Iron deficiency anaemia

» May be regenerative- depends on stage of

process

evidence of regeneration

» May take 3-5 days to be seen in peripheral blood

» Polychromatophils see on standard stain

• Purple staining

• Usually larger in size

» New Methylene Blue stain

• Ribosomes and Polyribosomes stained by supravital stain

» Younger erythrocytes

• Increased MCV (Mean Corpuscular Volume) stands for mean corpuscular volume, which measures the average size of your red blood cells)- macrocytic

• Decreased MCHC (mean corpuscular hemoglobin concentration, which is a measurement of the average concentration of hemoglobin inside your red blood cells)- hypochromic

• Increased RDW (red blood cell distribution width)- anisocytosis (cell size variation)

Evidence of Iron (Fe) Deficiency- (Chronic Blood loss)

» Hypochromic cells, with pronounced central pallor

» Decreased MCV- microcytic

» Decreased MCHC- hypochromic

» With progression – microcytic, hypochromic, anaemia

• But one may develop before the other.

» May have other morphologic changes

• Red cell fragments, schistocytes, elliptocytes

» Initially will be regenerative

• Over time – when Fe deficiency is severe- progress to non-regenerative

» Most often chronic external blood loss

• May be dietary deficiency (particularly young animals on a milk –fed diet)

anaemia - haemolysis

Mechanical or Due to Cell Damage or Defects

» Morphology often extremely helpful

• Heinz Body Haemolytic Anaemia

• Heinz bodies- oxidative damage

• Eccentrocytes- oxidative damage

• Schistocytes- shear damage

» Morphology often indicates underlying

pathophysiology -> suggests likely differentials

Immune Mediated Destruction

Immune mediated haemolytic anaemia (IMHA)

» Morphology can be helpful- additional testing

required

• Spherocytes (without schistocytes!)

» May be idiopathic (dont know the cause)/primary autoimmune

» May be secondary e.g. to infectious disease,

lymphoid neoplasms, histiocytic disorders

» ‘Other’ – e.g. Neonatal Isoerythrolysis

Significant Anaemias often present with a mix of both processes in haemolysis

Intravascular

» Lysis of blood cells within vessels

• Does not include sinuses of liver, spleen or bone marrow

» Severe or rapidly falling anaemia

» Present over hours or days

» Haemoglobinaemia (but may not be grossly visible)

» Haemoglobinuria

» Hyperbilirubinaemia- variable

» Bilirubinuria- variable

Extravascular

» Erythrocyte lysis outside of blood vessels

• Within macrophages- (not due to clearing haemorrhage)

» Mild to marked anaemia

» Presents over days or weeks

» Haemoglobinaemia and haemoglobinuria not present

» Hyperbilirubinaemia and hyperbilirubinuria usually present

• In blood unconjugated bilirubin> conjugated bilirubin

Haemolytic icterus (jaundice) – Pre-hepatic

» Pathologic haemolysis -> increased Hgb degradation -> increased bilirubin formation

» Bu (unconjugated bilirubin) travels to liver via tissue macrophages

• Generally liver has large capacity for uptake and conjugation

» Rate limiting step is usually the transport of Bc (conjugated bilirubin) to the biliary system for excretion

• If this is exceeded then Bc is ‘regurgitated’ out into plasma

» Bc then competes for uptake with Bu- so both forms increase in circulating plasma

oxidative injury

» Heinz bodies and Eccentrocytes

» Overwhelming of reductive pathways that keep Hgb in reduced state

» Hgb-Fe2+ undergoes spontaneous conformational change-> hemichromes

» Hemichromes of heme depleted Hgb precipitate -> Heinz bodies

» Erythrocytes are less deformable

• Trapped in spleen and lysed

» Structural damage caused by oxidation -> fragile cells

» Redistribution of band 3 proteins (Heinz bodies)->

• Antibody binding

• Removal by macrophages in spleen and liver

erythrocyte fragmentation

» Schistocytes-fragmented pieces of red blood cells that form when cells are physically torn apart by mechanical damage or tight fibrin strands in blood vessels

» Keratocytes (helmet cells)- can be seen in vitro in feline samples

» Acanthocytes

» Spherocyte-like cells

» Multiple pathogenesis suspected

• Trauma by relatively rigid structures e.g. fibrin

• Rheologic forces

uncommon

» Defects in ATP generation

• PK deficiency (Pyruvate kinase deficiency)

• Moderate anaemia, moderate to extreme reticulocytosis, mild to moderate icterus

• May progress to myelofibrosis -> pancytopenia

• PFK deficiency

• First noted in English Springer Spaniels, now reported in other breeds including American Cocker Spaniels

• Anaemia, haemoglobinaemia, haemoglobinuria after hyperventiliation (producing a respiratory alkalosis) and haemolytic icterus

• When not actively haemolysing then mild regenerative anaemia

» Hypophosphataemic haemoglobinuria in cattle

• Postparturient- 3-8 weeks after calving.

• Defective mobilisation of phosphorus from bone -> defective erythrocyte ATP production -> haemolysis

IMHA

» Idiopathic (presumptive primary autoimmune)

» Drug induced

» Vaccine induced

» Alloimmune

• Neonatal isoerythrolysis

• Blood transfusion reactions

» Secondary to increased Ig production eg lymphoma

IMHA blood smear

» Haemolysis

» Erythrocytes coated in erythrocyte surface associated immunoglobulin ESAIg and/or C3 undergo extravascular haemolysis (removed)

» Erythrocytes coated in erythrocyte surface associated immunoglobulin ESAIg and/or C3 -> Spherocytes due to macrophage removing portion of membrane

• Spherocytes may undergo

• Intravascular haemolysis (fragility) OR

• Extravascular haemolysis (rigidity)

» ESAIg may also bind complement -> activation of complent cascade

• Intravascular haemolysis

Haemolysis – Infectious–IMHA and/or other mechanisms

» Mycoplasma spp.

» Leptospira spp.

» Anaplasma spp.

» Clostridium spp.

• Bacillary haemoglobinuria

• Yellow lamb disease (Clostridium perfringens)

• Clostridial infections in horses

» EIAV – Equine Infectious Anaemia Virus- Swamp fever- NOTIFIABLE

» FeLV – Feline Leukaemia virus

» Ehrlichia spp.

» Babesia spp.

» Theileria spp.

» Trypanosoma spp.

IMHA in saline

» Persistence of agglutination

» Despite dilution with saline

» Dilution factors can be variable

» Often start at 1:2 -> 1:4

» Confirm on 1:10 dilution

• 1 part blood 9 parts saline

agglutination

drug induced IMHA

» Not common- three major mechanisms considered

• Drug adsorption- e.g. penicillin binds covalently to erythrocytes and stimulates hapten-dependent antibodies

• Autoantibody induction- induces formation of autoantibodies – antibodies can bind to normal erythrocytes in absence of drug

• Drug-dependent antibody induction- induces antibodies only when soluble drug is present.

» Penicillin – horses

» Cephalosporins- dogs

» Methimazole (rarely reported)– cats

Neonatal Isoerythrolysis-a life-threatening, immune-mediated blood disorder where a newborn's red blood cells are destroyed by maternal antibodies absorbed through colostrum

» Dam (or Queen) negative for blood factor mates with Sire positive for blood factor

» Foetus is positive for blood factor

» Mare- Leakage of blood across the placenta during pregnancy leads to development of antibodies to the blood factor during pregnancy (and persistent beyond this pregnancy)

» Queen- alloantibodies already present

» Equine Qa and Aa factors most often implicated.

» Feline Group B Queen to A or AB kittens

» Dogs usually only an issue if DEA 1.1. negative bitch has had a blood transfusion with DEA 1.1 +ve blood and had sufficient time to produce antibodies prior to colostrum intake

presentation

» Typically normal at birth

» Signs may develop as early as 5 hours- more usually 12-48 hours

» Subacute to peracute

» Lethargy, weakness, tachypnoea, icterus, pigmenturia, haemodynamic shock,

can be fatal

» Spun PCV from a Neonatal isoerythrolysis foal

• Initial sample on left- haemolysed/haemoglobinaemia

• Follow up sample 5 days later- icteric/bilirubinaemia

• NB neonates often have higher levels of bilirubin

EIAV- Equine Infectious Anaemia Virus

» Confirmed infected animals – destroyed

» In contacts restricted and tested twice in a 90 day period

» Coggins test – gold standard (Agar gel immunodiffusion AGID)

• ELISA test also available – possible false positive- confirm positives with Coggins Test

» Can get a false negative in acute stage- consider retesting 10-14 days after presentation

» Presentation can be variable, acute, subacute, chronic and carrier

EIAV- Equine Infectious Anaemia Virus

» Confirmed infected animals – destroyed

» In contacts restricted and tested twice in a 90 day period

» Coggins test – gold standard (Agar gel immunodiffusion AGID)

• ELISA test also available – possible false positive- confirm positives with Coggins Test

» Can get a false negative in acute stage- consider retesting 10-14 days after presentation

» Presentation can be variable, acute, subacute, chronic and carrier

Mycoplasma spp.

» Feline

• Mycoplasma hemofelis (not be confused with Mycoplasma felis)

• Mycoplasma haemominutum

• Mycoplasma turicensis

» Alpaca

• Mycoplasma haemolamae

» Cattle

• Mycoplasma weyonii

» Pigs

• Mycoplasma haemosuis, and Mycoplasma parvum

» Dogs

• Mycoplasma haemocanis

» PCR often more sensitive than blood smear examination

» Numbers of circulating organisms can be variable.

babesia

» Babesia canis reported in non-travelled UK dogs

Anaemias

Decreased Production

Reduced erythropoesis

» Decreased erythropoietin

» Refractory to erythropoietin

» Primary bone marrow disorder

• Damage

• Displacement/Replacment

Ineffective erythropoesis

» Destruction of erythrocyte precursors

» Defective erythrocytes

• Defective heme synthesis

• Abnormal erythroid maturation

• Defective nucleic acid metabolism

non-regenerative anaemias

» Whether anaemias are due to decreased or ineffective erythropoiesis –> non-regenerative

• Absence of reticuolcytes or polychromatophils in peripheral blood (and within bone marrow samples)

• Usually normocytic, normochromic, non-regenerative (anaemia present >5 days)

» Bone marrow disorders e.g.

• Haematopoetic neoplasia- damage or replacement of bone marrow by neoplastic population

• -Pure Red Cell Aplasia (PRCA)- possible immune mediated component -?destruction of early erythroid

• Myelofibrosis- can be a sequalae of PK deficiency

• Damage following inflammation, necrosis, toxicosis (e.g. oestrogen),

Anaemia of Chronic or Inflammatory Disease

» Mild, normocytic, normochromic, non-regenerative anaemia

• Most common cause of anaemia in veterinary patients

• Requires treatment of the underlying disease to resolve the anaemia

• Anaemia likely does not require further investigation, unless persistent, progresses to moderate/marked

» Inflammation -> shortened erythrocyte lifespans

» Inflammation and/or other -> sequestration of Fe – so unavailable for erythrocyte production

• Hepcidin production increased in response to IL-6 -> hepcidin binds to ferroportin -> internalises ferroportin so no longer in membranes -> macrophages cannot export Fe

• Alterations in ferritin production and transferrin receptors -> increased Fe storage and decreased availability

• Number of other cytokines have effects on Fe kinetics

» Inflammation -> cytokines reduce erythroid cell response to EPO and may reduce amount of EPO produced

non-regenerative anaemia - reduced erytropoeisis

» Normocytic, normochromic, mild to moderate -> severe if persistent

» Renal disease- chronic kidney disease

• Decreased production of EPO

» Endocrine

• Hypothyroidism

• Hypoadrenocorticism

• hypoandrogenism

» Liver disease or failure

Non-regenerative anaemia – Ineffective erythropoesis

» Nutritional deficiencies

• Fe – microcytic, hypochromic

• Folate or Cobalamin (B12) – normocytic, normochromic

• In humans macrocytic- not usually seen in veterinary species

• Dog breeds eg Giant Schnauzer – inherited malabsorption of B12

• Cattle – cobalt deficient soil grazing

• Copper- functional Fe deficiency- microcytic, hypochromic

» Inherited diseases

• Dyserythropoesis of English Springer Spaniels

• Congenital dyserythropoesis of polled Hereford calves

» FeLV- may cause hypoplasia (reduced) or erythroid neoplasia (ineffective) – macrocytic, normochromic

anaemias summary

Polycythemia or Erythrocytosis

» Increased red cells- if severe/persistent then may have sluggish movement of blood through vessels

» May be relative erythrocytosis- increased PCV in response to reduction in water e.g dehydration

» May be splenic contraction (physiologic erythrocytosis)– excitement

» May be pathologic

• Primary- polycythemia vera

• Secondary

• Appropriate- response to cardiac or respiratory disease, hyperthyroidism

• Inappropriate- e.g. Renal tumour-> hypoxia of renal tissue-> increased erythropoietin production, or other non-renal neoplasms