Equine clinical pathology Flashcards
Causes of anaemia
Loss of red cells (haemorrhage)
Destruction of red cells (haemolysis)
Reduced production of red cells (by bone marrow)
Anaemia on cytology
the reticulocytes produced in the marrow are not released into the circulation in significant numbers, and so we do not see polychromasia or reticulocytosis in anaemias secondary to haemorrhage or haemolysis in horses
WHen do features of regenerative anaemia become evident in the circulating blood?
3-5 days following haemorrhage/haemolysis
Signs of regenerative anaemia
Macrocytosis (↑ MCV)
Increased red cell distribution width (RDW)
Anisocytosis on blood smear
Serial increase in PCV over time – provided plasma protein does not also increase, otherwise this could reflect dehydration
cells remain normochromic, so a reduction in MCHC is not seen
definitively diagnosed based on the finding of increased numbers of polychromatophils on bone marrow cytology - impractical
DDx for regenerative anaemias in horses
Haemorrhage
- external
- internal
Haemolysis
- IMHA
- oxidative damage
- Equine infectious Anaemia Virus
- Piroplasmosis
Locations of external haemorrhage in horses
E.g. guttural pouch, urinary, GI
IMHA in horses
Primary
Secondary
□ Infectious agents
® Clostridia
® Rhodococcus
® S. equi
□ Neoplasia
® Lymphoma (usually)
□ Drugs
® Penicillin
® TMPS
Causes of oxidative damage in horses
Onion
Red maple leaves
Equine Infectious Anaemia Virus (EIAV)
Notifiable!!
Seen in imported horses or those recieving imported blood products
Piroplasmosis in horses
Babesia, Theileria
Seen in imported horses
Differential diagnoses for non-regenerative anaemia in horses
Pre-regenerative
- re-check in 3-5days
Mild-moderate:
- anaemia of inflammatory/neoplastic diseases,
- anaemia secondary to chronic liver disease
- anaemia of chronic kidney disease
Moderate-marked:
- phenylbutazone toxicosis,
- chloramphenicol toxicosis,
- myelofibrosis,
- leukaemia
How much of teh total red blood cell mass is the speel capable of storing?
Up to 50%
Which hormone can induce splenic contraction?
Adrenaline
Can mask an underlying anaemia but should normalise within 40-60mins
When can splenic sequestration occur?
when horses are anaesthetised
this can lead to a reduction in PCV/HCT that can mimic anaemia
Blood groups in horses
complicated system of blood groups with eight main blood groups.
The EAA and EAQ groups are associated with the most transfusion reactions and neonatal isoerythrolysis cases and around 10-20% of horses will have naturally occurring alloantibodies, hence if blood transfusion is needed, then cross matching should always be performed prior to transfusion, in order to minimise the chances of transfusion reactions occurring.
Causes of neutrophilia in horses
can occur secondary to systemic inflammation, and it is uncommon to see left shift in these cases although toxic changes are sometimes seen.
Alternatively mild neutrophilia can occur secondary to endogenous (chronic stress) or exogenous steroids.
When can neutropenia be seen in horses?
associated with severe systemic inflammation (e.g. septic peritonitis) or endotoxaemia.
If monocytosis reflective of systemic inflammation in horses?
No - not part of the stress leukogram in horses
Most commonly used acute phase protein in horses
Serum amyloid A
- from <0.5 to >100ug/dL
Can also use fibrinogen
- less of an increase and takes longer
Markers of hepatocellular damage in horses
SDH, AST, GLDH
NOT ALT
Markers of biliary epithelial cell injury in horses
GGT and ALP
SDH
located in the hepatocyte cytoplasm
activity in serum will peak at around 2 days post injury, and normalise within 3 days
needs to be analysed within 4 hours
AST
located in the cytoplasm and mitochondria of hepatocytes
marker of more severe hepatocyte injury
less specific for hepatocellular injury as also in myocytes and RBCs (look at CK as well)
reach peak activities in serum at around 3-4 days post injury, and may be elevated for up to 10 days
GLDH
mitochrondrial location
marker of more severe (and irreversible) hepatocyte injury
reach peak activities in serum at around 3-4 days post injury, and may be elevated for up to 10 days
GGT
marker of biliary cell injury
increased in cholestasis or biliary hyperplasia
can also be released in small amounts in hepatocellular injury
ALP
marker of biliary cell injury but is considered less sensitive for this than GGT
Funtional hepatocellular markers
bile acids, ammonia and total bilirubin
bile acids and total bilirubin can be increased by other factors
Other non-specific biochemical markers of hepatic function include albumin, urea and cholesterol
animals with significant hepatocellular dysfunction can have low serum albumin, urea and cholesterol concentrations.
Serum bile acid concentration
more specific for hepatocellular dysfunction than serum bilirubin concentrations, however these can also be increased in cholestasis.
However no post prandial increases in serum bile acids occur because horses lack a gall bladder.
Total bilirubin concentrations
Increase while fasting because fasting causes mobilisation of fatty acids from fat into the circulation, and these fatty acids compete with bilirubin for uptake into hepatocytes.
What can hyperbilirubinaemia be associated with?
hepatocellular dysfunction, fasting cholestasis and haemolytic disorders.
Acute kidney injury - bloodwork
usually azotaemic with urea : creatinine ratios <10.
It is also common for renal tubular reabsorption of sodium and chloride to be reduced and so they become hyponatraemic and hypochloraemic secondary to urinary sodium and chloride losses.
Chronic kidney disease - bloodwork
azotaemic, with urea : creatinine ratios >10.
often hypophosphataemic, and hypercalcaemic (dependent on food and calcium intake).
can also be hyperkalaemic.
Urinalysis of healthy horse
should have urine specific gravity of > 1.020, and it is common for equine urine to contain high numbers of calcium carbonate and calcium phosphate crystals.
Hyponatraemia in horses
can occur secondary to loss of isotonic fluids with subsequent fluid repletion, and this can occur due to GI sequestration of fluids as may occur in ileus, GI obstruction or gastric reflux.
Equine sweat is also slightly hypertonic, and so exercise and sweating can also lead to sodium losses and hyponatraemia.
Hypocalcaemia in horses
can be associated with colic
reported secondary to heavy exercise in horses due to calcium losses in sweat and metabolic alkalosis leading to increased calcium binding to proteins (thus reducing ionised calcium concentrations).
Lipid metabolism in horses
Triglycerides are hydrolysed in the intestine by pancreatic lipases before being absorbed by small intestinal enterocytes and then packaged with proteins to form chylomicrons
Removal of lipids from the circulation
by lipoprotein lipases which hydrolyse lipoproteins to release fatty acids, that can in turn be stored as TGs in muscle and adipose tissues or used as an energy source.
Lipoprotein lipase activity is enhanced by insulin.
Liberation of fatty acids from TGs in storage sites
catalysed by hormone sensitive lipases, the activity of which is enhanced by cortisol, adrenaline and glucagon.
Hyperlipidaemia
Mild to moderate increase in serum triglyceride concentrations (<5.7 mmol/L)
No gross lipaemia in sample
No clinical signs, often subclinical
Hyperlipaemia
Marked increase in serum triglyceride concentrations (>5.7 mmol/L)
Gross lipaemia in sample
Fatty infiltration of liver and other organs
Cause of hyperlipidaemias
usually occur secondary to underlying pathology which causes hyporexia (e.g. colic) and/or negative energy balance (e.g. pregnancy/lactation).
Glucagon is increased in periods of hyporexia/negative energy balance and cortisol/ACTH/catecholamines are all increased in illness, and these hormones all stimulate hormone sensitive lipase to mobilise fatty acids.
Some animals can get primary hyperlipidaemias (i.e. within underlying pathology) and these are more common in ponies (e.g. Shetlands) and donkeys and in obesity.
Cause of hyperlipaemia
usually occurs when there is additional factors that cause insulin resistance.
How much peritoneal fluid is normal in horses?
10-100mL
How much pleural fluid is normal in horses?
<8mL
Normal colour of body cavity effusions in horses
Slightly yellow, clear appearance.
Make up of normal body cavity effusions in horses
tend to have higher protein concentrations (up to 35 g/L) and nucleated cell counts (up to 12.0x10^9/L).
higher percentages of neutrophils compared with dogs and cats.
Transudates
diagnosed when an increased volume of effusion is noted and the fluid cell count is <10-12 x10^9 cells/L.
Protein poor transudates
fluid protein concentrations < 20g/L and can be associated with marked hypoalbuminaemia, acute uroabdomen or disorders that cause lymphatic obstruction
E.g. acute intestinal volvulus or torsion
Protein rich transudates
fluid protein concentrations > 20 g/L and can be associated with increased hydrostatic pressure in the vasculature that is causes by right sided congestive heart failure or portal hypertension.
These effusions can also be associated with chronic uroabdomen or neoplasia.
Exudates
high fluid nucleated cell counts (>10 x10^9 cells/L – usually higher)
Septic exudates
intracellular bacteria within neutrophils
Measurement of fluid and serum glucose can be performed, and if the fluid glucose is >2.8 mmol/L lower than that of the serum, then this is supportive of a septic aetiology.
Non-septic exudates
can occur secondary to ischaemic necrosis
Fluid lactate concentrations >1 mmol/L are supportive of ischaemic necrosis
higher fluid lactate concentrations are associated with a worse prognosis in both strangulating and non-strangulating lesions.
Non septic exudates can also be seen in neoplasia and in pancreatitis or bile leakage.
Septic joint fluid
usually have high numbers of neutrophils present on the slide (>10 per 40x field), although bacteria are usually not seen.
Evaluation of joint fluid cell counts
determined using an automated analyser, however because the fluid is quite viscous, sometimes it cannot pass through the narrow probe which draws the sample into the machine.
In these cases, the addition of hyaluronidase to the fluid (to break down the hyaluronic acid which gives joint fluid its viscous characteristic) may enable the fluid cell count to be determined.
cytology of the fluid to confirm the cells are neutrophils
Chemical synovitis
can be associated with joint fluid nucleated cell counts of up to 30 x10^9 cells/L (although usually <10 x10^9 cells/L).
What nucleated cell count would be informative as to whether or not a joint is septic?
> 100x10^9 cells/L are highly likely to be due to septic arthritis
Fluid cell counts would be considered abnormal when >10 x10^9 cells/L
Most useful findings on BAL
Neutrophilic inflammation
Haemorrhage
Neutrophilic inflammation on BAL
septic (e.g. bacterial) and non-septic causes
most common non-septic causes are equine asthma syndrome
BAL culture is recommended to rule out concurrent septic causes
Severe equine asthma syndrome on BAL
tends to affect older, stabled horses which have increased respiratory effort at rest in addition to exercise intolerance.
On the BAL there is increased neutrophils (>20%) and increased mucus
Mild-moderate equine asthma on BAL
tends to affect horses of any age, they tend to have minimal/subtle clinical signs at rest and their BALs tend to be less neutrophilic (<20%) and can contain increased numbers of mast cells, eosinophils and lymphocytes
Haemorrhage on BAL
can indicate exercise induced pulmonary haemorrhage (EIPH) which occurs following strenuous exercise
Exercise induced pulmonary haemorrhage on cytology
may be large numbers of erythrocytes, however the diagnosis would be made if macrophages containing haemosiderin (haemoglobin breakdown products) are seen in large numbers (usually >50%).
