Clinical Pathology: Equine Clinical Pathology and Anaemia Flashcards
What must be considered about clinicopathological tests available in horses?
Accuracy, Precision
Sensitivity and Specificity
What is sensitivity and specificity?
Sensitivity- % of disease positive animals that correctly identified as positive
Specificity- % of disease negative animals that correctly identified as negative
What is PPV and NPV?
PPV- % of positive results that are actually positive
NPV- % of negative results that are actually negative
What can be used for diagnosis of laminitis risk in ponies?
Adiponectin concentration- hormone from fat
What is haematology, histology, cytology, urinalysis, coprology and serology?
Haematology- morphology of the blood and blood forming tissues
Histology- microscopic structure composition and function of tissues
Cytology- cells their origin, structure, function and pathology
Urinalysis- urine test
Coprology- shit
Serology- study of serum
What is the difference between serum and plasma?
Serum is allowing a clot and then taking centrifuged fluid- plasma with coagulation proteins removed
Plasma is mixing with anticoagulant then centrifuging
How does breed affect PCV, red blood cell count and haemaglobin?
Hot blooded horse has a higher PCV, RBCC, and haemoglobin
What blood proteins are there?
How is it measured?
What can affect the results?
Blood proteins- albumin, globulin, fibrinogen
Measured as total protein on refractometer
Icterus, lipaemia, haemolysis affect results
What does albumin do?
Controls colloid oncotic pressure
Binds cations and hormones
Binds to drugs
What different proteins show on serum protein electrophoresis?
Albumin
Y globulins- immunoglobulins
A- globulins- acute phase protein, a-lipoproteins, antithrombin III
B-globulins- complement, transferrin, plasminogen
What is hyperproteinaemia and what is a common cause?
Increases total protein- albumin, globulin or both
Dehydration
What is hyperglobulinaemia and what is the most common causes?
Increased globulins
Most common causes are chronic inflammation or tumour of B lymphocytes
What is panhypoproteinaemia?
Aggressive intravenous therapy causing severe protein loss
What can cause hypoalbuminaemia?
Albumin is a small molecule therefore
More loss across intestinal mucosa/glomerulus
Loss of effusion
Decreased production
What does hypoproteinaemia often cause in horses?
Pitting ventral oedema
What can cause oedema?
Increased hydrostatic pressure
Decreased oncotic pressure
Increased permeability
Impaired lymphatic drainage
What is a myopathy?
A disease of the muscle
What are the clinical signs of liver disease in horses?
Varied and non-specific
Weight loss
Colic
Anorexia
Photosensitisation
Neurological signs
Diarrhoea
Jaundice
What enzymes would be released from damage to the liver?
GGT
GLDH
AST
ALP
LDH
What is anaemia?
What three mechanisms can produce anaemia?
Anaemia is a reduction in circulating red blood cell volume or haemaglobin concentration
Blood loss
Increased RBC destruction
Decreased RBC production
Why should horses PCV not be assessed after or during excercise?
The spleen in horses is a reservoir for erythrocytes- PCV can increase by 0.25L/L
Also a platelet reservoir- 1/3 of platelets
What are the clinical signs of anaemia in horses?
Lack of oxygenation
Tachypneoa, tachycardia
Pallor
Excercise intollerance, lethargy, weakness- collapse
Underlying disease process
Fever, ictus, pigmenturia
What is hypovolaemic shock and what are its clinical signs?
When do clinical signs show?
A form of shock caused by severe hypovolaemia
Tachycardia
Tachypnoea
Hypothermia
Pale and dry mucous membranes
Prolonged CRT
Weak pulse
Cold extremities
Muscle weakness
Clinical signs of shock become apparent after 30% of blood loss
How is anaemia diagnosed in horses?
PCV-
Normal throroughbreds- 35-45%, Ponies and draught breeds 26-35%
History and clinical exam
External/internal blood loss
Evidence of clotting disorder
Evidence of haemolysis
Initial labs- complete blood count, total plasma protein, plasma fibrinogen, lactate, RBC morphology
What compensatory mechanisms for anaemia do horses have?
Spleen can mask the extent of blood loss for several hours post haemorrhage
Catecholamines induce vasoconstriction and increase cardiac output
Plamsa volume is expanded by withdrawl of fluid from the interstitium and increased reabsorption of water in the renal tubules via ADH
Fluid movement into the vascular system continues
Decline in the TPP
Decrease in PCV not seen till 12-24 hours post haemorrhage
Why is it difficult to diagnose regenerative vs non-regeneratvie anaemia in horses?
Peripheral signs of regeneration such as reticulocytosis and polychromasia rarely occur
Bone marrow evaluation may be required to confirm non-regeneratvie myeloid disorders
How can regenerative anaemia be diagnosed in horses?
Regenerative anaemia without anthing else casues hypoproteinaemia
Diagnostic evaluation of suspected haemolytic anaemia should inclue thorough blood smear, urinalysis, coombs and coggins test
What might be seen in a horse with haemolysis in its smear?
Spherocytes, heinz bodies, saline agglutination, erythrocye osmotic fragility and coombs test
What are the differential diagnoses for horses with anaemia?
Acute blood loss anaemia
Coagulopathies
Chronic blood loss anaemia
Haemolytic anaemia
Blood parasites
EIA
Oxidant induced haemolytic anaemia
Non-regen anaemia
What can cause acute blood loss anaemia?
Haemorrhage due to traumatic or surgical wounds
Guttural pouch mycosis
Uterine artery rupture
Mesenteric artery rupture- rare
Epitaxis- nose bleed- rare
Tumours- splenic disease, haemangiosarcoma
Thoracic large vessel rupture in race horses
Renal haemorrhage
Rib fracture- especially foals
What can cause coagulopathies in horses?
Rare- usually DIC consumptive coagulopathy secondary to sepsis, severe systemic inflammation vs inherited
Secondary to liver disease
How does chronic blood loss anaemia develop and what can cause it?
Allow the bone marrow to regenerate erythrocytes as they are lost, therefore anaemia only develops once the rate of erythropoiesis is exceeded by the rate of haemorrhage
Gradual tissue hypoxia allows physiological adaptation so clinical signs of anaemia masked until PCV drops <0.15l/l
Usually GIT bleeding- parasitic, neoplasia, gastric/duodenal ulceration, NSAID toxicosis, may be urogenital
What can cause haemolytic anaemia?
True immune mediated haemolytic anaemia rare
More likely secondary haemolytic:
Penacillin reaction
Clostridium perfringens
Injection site abscess
Lymphoma
What is EIA?
What blood parasites can cause anaemia?
Equine infectious anaemia- ehrlichiosis
Babesia divergens cause anaemia
What can cause non-regenerative anaemia in horses?
Bone marrow disorders
Anaemia of chronic disease
Iron deficiency- uncommon
Folic acid deficiency
How is acute blood loss diagnosed?
What are the treatment aims?
Based on history of recent haemorrhage, clinical signs and eventual development of anaemia accompanies by hypoproteinaemia
Identification and elimination of the cause, provision of nursing cate, ensuring adequate tissue perfusion, minimising stress
How can acute blood loss be diagnosed?
Blood transfusion is inadequate to support life
Stop bleeding- ligation, haemostats, pressure bandage
Unable to stop bleeding- permissive hypotension, maintain enough blood pressure to deliver O2 to heart/brain
Once bleeding stopped- replace circulating volume- hypertonic saline, crystalloids, colloids
Adjunctive therapy- iron, vit B12, anabolic steroids, corticosteroids, Vit C or antioxidants
Blood transfusion when >30% blood volume lost, clinical signs of hypovolaemic shock
What is anaemia?
What are the three physiological mechanisms of anaemia?
A reduction in circulating red blood cell volume or haemoglobin concentration
Functionally defined as decreased oxygen-carrying capacity of the blood
occurs when the PCV is reduced below that which is considered normal for the horses are, breed and use
Mechanisms
Blood loss
Increased destruction
Decreased production
Why does the spleen need to be taken into consideration for horses anaemia?
Reservoir for erythrocytes- PCV can increase by 0.25L/L
Also a platelet reservoir (1/3)
Therefore don’t assess Horses during or after exercise
Why do clinical signs of anaemia vary and what are the clinical signs?
Depends on how rapidly it develops
CS:
- Lack of oxygenation, tachypnoea, tachycardia
- Pallor
- Excercise intolerance, lethargy, weakness- collapse
- Underlying disease process- haemorrhage, pyrexia, anorexia, weight loss
- Fever, icterus, pigmenturia may accompany haemolysis
- Epistaxis, haematuria or melaena may signal chronic blood loss
What are the clinical signs of hypovolaemic shock?
- Tachcardia
- Tachypnoea
- Hypothermia
- Pale and dry mucous membranes
- Prolonged CRT
- Weak pulse
- Cold extremities
- Muscle weakness
- Clinical signs become apparent after 30% of blood loss- 500kg = 13L
What is the normal PCV in TB, Ponies and Draught breeds?
How is anaemia diagnosis approached?
Normal PCV- TB 35-45%, Ponies and Draughts (26-35%)
- History and clinical exam
- Acute or chronic
- External/internal blood loss
- Evidence of a clotting disorder
- Evidence of haemolysis
- Initial labs- complete blood count, total plasma protein, plasma fibrinogen, lactate
- RBC morphology
What are the compensatory mechanisms for anaemia in horses?
- Spleen- masks the extent of blood loss for several hours post haemorrhage
- Catecholamines induce vasoconstriction and increase cardiac output
- Plasma volume is expanded by the withdrawal of fluid from the interstitium and increased reabsorption of water in the renal tubules and GI by ADH
- Fluid movement into the vascular system continues
- decline in the TPP
- Decrease in PCV not seen until 12-24 hr post haemorrhage
How is regenerative or non-regenerative anaemia distinguished?
Peripheral signs of regeneration such as reticulocytosis and polychromasia rarely occur in horses
Howell-Jolly bodies are occasionally found in eryhrocytes
Bone marrow evaluation may be required to confirm non-regen myeloid disorders
Diagnosis- rule in or out haemolysis
- Pink plasma if intravasculae
- Regenerative anaemia without concomitant hypoproteinaemia
- Diagnostic evaluation of suspected haemolytic anaemia- should include a thorough blood smear, urinalysis, coombs, Coggin
- Smear- spherocytes, Heinz bodies
- May see an increase in free HB, MCH, MCHC
What are the most likely differentials for clinical presentations of anaemia?
Acute blood loss anaemia
Coagulopathies
Chronic blood loss anaemia
Haemolytic anaemia
Blood parasites
Oxidant induced haemolytic anaemia
Non-regen anaemia:
bone marrow disorders, anaemia of chronic disease, iron deficiency, folic acid deficiency
What can cause acute blood loss anaemia in horses?
- Haemorrhage due to trauma or surgical wounds
- Guttural pouch mysosis
- Uterine artery rupture
- Mesenteric artery rupture- rare
- Epistaxis rare
- Tumours- splenic disease, haemangiosarcoma
- Thoracic large vessel rupture in race horses
- Renal haemorrhage
- Rib fracture
What can cause coagulopathies in horses?
Rare-
usually DIC secondary to sepsis or severe systemic inflamation
or
Secondary to liver disease
How is chronic blood loss different to acute?
What can cause chronic blood loss anaemia in horses?
What causes haemolytic anaemia?
Chronic- allows the bone marrow to regenerate, anaemia only develops once erythropoiesis is exceeded by the rate of loss
Chronic anaemia causes-
Usually GIT- parasitic, neoplasia, gastric/duodenal ulceration, NSAID toxicosis
Maybe urogenital blood loss
Haemolytic anaemia-
True immune-mediated haemolytic anaemia is rare, more likely secondary (penicillin, C. perfringens, injection site abscess, lymphoma)
Neonatal isoerythrolysis- immune-mediated anaemia
What are the aims of treating anaemia?
How is it treated?
Aims-
Identification, elimination of the cause, and provision of nursing care, ensuring adequate tissue perfusion, minimising stress
Treatments-
- Stop bleeding- ligation, haemostats, pressure bandage
- Unable to stop- permissive hypotension, maintain BP for brain/heart, do not dilute RBCs and increase haemorrhage
- Stopped bleeding- replace circulating volume- hypertonic saline, crystalloids, colloids, blood transfuction
Adjunct therapy- Iron, Vit B12, Anabolic steroid, Corticosteroids, Vit C or antioxidants
Blood transfusion- when >30% blood volume loss, increased latate PCV<15%
How is the amount of blood volume needed worked out for transfusion?
Blood volume = 80ml/kg
Blood deficit = (normal PCV - animal PCV) x (0.08 x weight)
