Anaemia

1. HAEMORRHAGIC ANAEMIAS
    may be little initial change in haematological and serum biochemical markers
    consider the following to search for a source of possible blood loss:
   o Rectal examination
   o Gastroscopy
   o Airway endoscopy
   o Ultrasonography
   o Abdominocentesis
   o Urinalysis
   o Faecal occult blood testing
2. HAEMOLYTIC ANAEMIAS

o Intravascular haemolysis where red cells are simply lysed, is more acute and
characterised by free haemoglobinaemia and haemoglobinuria
o Extravascular haemolysis where red cells are removed by macrophages in spleen
and other sites, is considerably more common. In such cases free haemoglobin is
not released into the circulation, although bilirubin is expected to be increased.
 Immune-mediated haemolytic anaemia (IMHA) is usually insidious in onset and clinical
signs may include pyrexia, lethargy and weight loss. May be primary idiopathic or
associated with infectious diseases, drugs (esp. penicillins) and neoplastic diseases.
 Neonatal isoerythrolysis is typically seen in multiparous mares and is likely to recur in
future pregnancies. Severe acute cases can be seen within hours of birth characterised by
collapse, tachycardia and pallor. Subacute cases can develop insidiously during the first
week of life and may show less dramatic signs including jaundice.
 Equine Infectious Anaemia (NOTIFIABLE!) should be considered as a potential cause of
haemolytic anaemia in imported horses or horses which have received imported blood
products. Diagnosis may be confirmed by the traditional Coggins test, ELISA or PCR.
 Piroplasmosis should be considered especially in imported horses infected with Babesia
caballi or Theileria equi. Diagnosis may be confirmed by IFAT, ELISA or PCR.

3. NON-REGENERATIVE ANAEMIAS
    Failure of bone marrow may be caused by myelophthisis (destruction of normal bone
   marrow structure) or aplastic disease (functional failure of stem cells).
    Myelophthisis is usually caused by neoplastic disease (especially lymphoma) but may also
   be caused by fibrosis within the bone marrow.
    Aplastic anaemia has been reported secondary to bacterial or viral infection, chronic
   renal or hepatic disease, neoplasia, irradiation, drug therapy (e.g. phenylbutazone and
   chloramphenicol) or autoimmune disease. May be temporary or permanent.

The 3 classes of anaemia are:

1. Blood loss
2. Haemolysis
3. Non-regenerative (failure of erythropoiesis)

HAEMORRHAGE HAEMOLYSIS MARROW SUPPRESSION
External Infectious Chronic haemorrhage
Guttural pouch mycosis Piroplasmosis Chronic inflammation
Ethmoid haematoma Equine Infectious Anaemia Chronic renal failure
Urinary (renal/bladder/urethra) Neoplasia (tissue)
Coagulopathy Immune mediated Neoplasia (myeloid)
Primary (idiopathic) Low iron intake
Internal Penicillin/beta lactam Myelofibrosis
Haemothorax Lymphoma Immune mediated disease
Splenic tear/neoplasia

Infectious (Piro,EIA,Strep,Clos-
tridia) Phenylbutazone toxicity

Mesenteric vessel rupture Neonatal isoerythrolysis Chloramphenicol toxicity
Uterine artery rupture Exogenous erythropoietin use
GI mucosal ulceration Oxidative injury Viral suppression
Phenothiazines
Onions
Red maple
Thermal burns

IMPORTANT CLINICAL SIGNS TO NOTE AND MONITOR
Behaviour – Depression/lethargy/poor performance – offers an indication of severity and acuity.
Mucous membrane colour – Peracute anaemias from haemorrhage or haemolysis usually show
pallor. Pallor might also occur with chronic non-regenerative anaemias although this is variable.
Subacute to chronic haemolytic anaemias are more likely to show jaundice.
Pyrexia – Common in cases of immune mediated (e.g. idiopathic IMHA, neonatal isoerythrolysis,
paraneoplastic) or infectious causes (piroplasmosis, EIA).
Tachycardia/tachypnoea – as a compensatory response to poor oxygen carrying capacity.
Pigmenturia – Discoloured urine may be a result of intravascular haemolysis and clearance of free
haemoglobin (haemoglobinuria), blood loss into urine (e.g. renal haemorrhage) or bilirubin excretion
as urobilinogen.
ASSESSMENT OF HAEMATOLOGY
Erythrocyte size (MCV) and morphology may give an indication of the cause of anaemia. However,
bear in mind that foals normally have small erythrocytes and donkeys have very large
erythrocytes. Erythrocyte size is a reasonable but not entirely reliable indicator of regeneration

and, as reticulocytes are not released into the peripheral circulation in horses, assessment of bone
marrow is a better means of classifying anaemia sub-types (see section on bone marrow
collection).
 low MCV (microcytic anaemia) may accompany iron deficiency or chronic disease.
 high MCV (macrocytic anaemia) typically accompanies haemolytic causes of anaemia or
haemorrhage and is an indicator of regeneration.
 high MCH or MCHC tends to suggest intravascular haemolysis (and free haemoglobin)
Blood smears should also be examined for:
 Schistocytes – haemolysis, DIC, neoplasia
 Heinz bodies or eccentrocytes – oxidant toxicity
 Howell Jolly bodies – regeneration
 Parasitaemia – Babesia caballi, Theileria equi
 Haemosiderophages – immune-mediated haemolysis?
 Spherocytes – immune-mediated haemolysis

SERUM BIOCHEMISTRY
Total serum proteins – Blood loss may be associated with hypoproteinaemia. Immune-mediated
haemolysis is often associated with increased globulins. Chronic inflammation, a frequent cause of
non-regenerative anaemia, may be associated with mild hypoalbuminaemia and
hyperglobulinaemia.
Acute phase proteins – Serum amyloid A may be increased as a result of inflammatory/neoplastic

lesions leading to blood loss, immune-mediated haemolysis or bone marrow suppression. Immune-
mediated haemolysis of various causes tends to be associated with an acute inflammatory response,

as do infectious diseases such as EIA and Piroplasmosis.
Bilirubin – haemolysis is typically associated with high total and indirect (unconjugated) bilirubin,
with normal direct (conjugated) bilirubin. Values are generally related to the acuity of the
haemolysis and can be >200 μmol/L. Other causes of increased bilirubin include anorexia which may
increase total values up to approximately 100 μmol/L (with normal direct fraction) and hepatic
insufficiency which will increase both indirect and direct fractions, with the latter fraction
occasionally >25% of total.

INVESTIGATING HAEMORRHAGIC ANAEMIAS
There may be little initial change in haematological and serum biochemical markers following whole
blood loss, as blood cells and plasma are lost in equal proportions and the spleen provides a reserve
supply of cells. By 24 hours, a decrease in PCV and RBC may be observed and there is usually an

accompanying hypoproteinaemia. Neutrophilia may be seen in some horses as a stress response. In
horses with acute or sub-acute haemorrhage clinical signs may develop when PCV drops to 15-20%.
In horses with more chronic haemorrhage clinical signs may not be seen until PCV drops to 12% or
less.
Consider the following to search for a source of possible blood loss:
Rectal examination – NB. Any faecal samples submitted for occult blood (see below) should precede
rectal examination.
Gastroscopy – bleeding gastric ulcers. Not a common cause of anaemia but is possible – especially in
foals/youngsters.
Endoscopy – for direct signs of bleeding and/or collection of tracheal wash/bronchoalveolar lavage
to look for presence of haemosiderophages (normal in exercising horses, abnormal in sedentary
horses).
Ultrasonography – haemothorax or haemoperitoneum may be evident as a cloudy, swirling effusion.
Abnormal masses may also be evident.
Abdominocentesis – for the presence of increased red cell content, phagocytosed red cells or
haemosiderophages.
Urinalysis – dipsticks will show “positive blood” if haemoglobinuria, haematuria or myoglobinuria is
present. Centrifugation and examination of sediment should enable differentiation of
haemoglobinuria from haematuria if the sample is fresh. Increased urobilinogen detected by
standard urine dipsticks supports a diagnosis of haemolysis.
Faecal occult blood testing is neither sensitive nor specific in horses.

INVESTIGATING HAEMOLYTIC ANAEMIAS
Most haemolytic anaemias in UK will be immune mediated or infectious.
Intravascular haemolysis (red cells simply lysed) is more acute and characterised by free
haemoglobinaemia and haemoglobinuria
Extravascular haemolysis (red cells removed by macrophages in spleen and other sites) is
considerably more common and the only indication that it is occurring may be slowly progressive
anaemia and the presence of spherocytes. Haemoglobinuria is not present.
Immune-mediated haemolytic anaemia (IMHA) is usually insidious in onset and clinical signs may
include pyrexia, lethargy and weight loss. Haematological analysis may reveal reduced RBC count,
increased spherocytes, macrocytosis, anisocytosis and biochemical analysis may reveal increased
bilirubin concentration. Identification of antibodies on erythrocytes with a Coombs test provides
further evidence of IMHA but is neither sensitive nor specific.
Primary idiopathic immune mediated anaemia in the absence of recognised causes does occur
although investigations should be performed into potential underlying causes. Many infectious
diseases, drugs and neoplastic diseases have the potential to trigger immune mediated haemolysis
Equine infectious anaemia (NOTIFIABLE!) should be considered as a potential cause of haemolytic
anaemia in imported horses or horses which have received imported blood products. Clinical signs

may be vague and can include recurrent pyrexia, weight loss and oedema in addition to anaemia.
Thrombocytopaenia is the most profound haematological abnormality. The diagnosis may be
confirmed by the traditional Coggins test, by ELISA or by PCR.
Piroplasmosis is another potential cause of haemolytic anaemia in imported horses (e.g. France,
Spain, Scandanavia, Americas) and is caused by infection with Babesia caballi or Theileria equi. The
potential for tick-borne spread within the UK exists.
The Direct Coombs test is used to examine for antibody (IgG and/or IgM) or complement attached to
erythrocyte membranes and may be positive in cases of immune-mediated anaemia. False negative
results are very common.

INVESTIGATING NON-REGENERATIVE ANAEMIAS
Sternal bone marrow aspirate and biopsy (see below) is a relatively straightforward procedure in
horses and aids significantly in the investigation of anaemias (as well as cases showing other
persistent abnormalities of leucocytes or platelets).
In normal horses there are similar numbers of cells from myeloid (WBC) and erythroid (RBC) series.
The reference range of the ratio of myeloid to erythroid cells is typically 0.5 to 1.5. Higher numbers
of erythroid series (low M:E ratio <0.5) infers a regenerative condition whereas lower erythroid series (high M:E ratio >1.5) infers non-regeneration.
Failure of bone marrow may be caused by myelophthitic disease (destruction of normal bone
marrow structure) or aplastic disease (functional failure of stem cells). Myeolphthisis is most
commonly caused by neoplastic disease (especially lymphoma) but may also be caused by
proliferation of fibrous tissue within the bone marrow. Aplastic anaemia has been reported
secondary to bacterial or viral infection, chronic renal or hepatic disease, neoplasia, irradiation, drug
therapy or autoimmune disease.
Whilst it is helpful to identify aplastic anaemia it is frequently impossible to determine the primary
cause of the aplasia although a presumptive diagnosis may be made from the horse’s hi story.
Aplasia associated with drug administration may be temporary or permanent. Phenylbutazone and
chloramphenicol have been reported as causes of aplasia.

Performing a bone marrow aspirate and biopsy

1. Collected from the sternum on the midline at the level of the points of the elbows in a horse
   standing square.
2. Following sedation and sterile preparation a 4 inch, 18-21 gauge spinal needle can be slowly
   “drilled” into the sternum and then the stylet removed and a 2 to 5 ml syringe attached
   containing a bead of EDTA solution in the hub.
3. A brief and gentle vacuum is then applied to the syringe in an attempt to obtain a single drop
   of bone marrow in the hub
4. Air-dried smears are then prepared and submitted for evaluation
5. If a free flowing sample is obtained this is likely to be heavily blood contaminated and
   unsuitable and if this is the case then a site slightly caudal or cranial to the original site is
   chosen and the procedure repeated. If no sample is obtained despite several attempts then
   the needle may be sitting in an intersternebral space rather than in a sternebra itself and the
   needle should be positioned a few centimetres in front or behind the previous site.
6. Ultrasound can be utilised to determine the position of the sternebrae but is not necessary
7. Bone marrow biopsy is performed at the same site with an 8 gauge Jamshidi needle which
   collects a small core of biopsy for a better evaluation of cell numbers within bone marrow.
   Biopsy provides considerably more information than aspirate alone