SA clinical pathology Flashcards
What liver features can be tested for by clinical pathology?
Hepatocellular injury -> leakage of enzymes
Cholestasis (reduced/blocked bile excretion) -> release of enzymes induced by retained bile
Hepatocellular function - decreased production or catabolism of substances
Hepatic portal circulation - decreased extraction of substances absorbed from GIT
Where are liver enzymes found normally?
ALP and GGT - on hepatocyte cell membranes
ALT, AST and SDH - in hepatocyte cytosol (and AST in mitochondria)
Which liver enzymes are there and what are they specific for?
ALT - largely liver specific (but also muscle), small animals
AST and LDH - liver and muscle
SDH and GLDH - liver specific in all species, used in large animals, SDH unstable
ALP and GGT - used in large animals as indicators of liver damage
What does it mean if there are increased liver ‘leakage’ enzymes in the blood?
Indicates hepatocellular damage
Myocyte damage can cause mild increase of AST, LDH +/- ALT (check CK)
Artefact (haemolysis) can increase AST and LDH (check serum/plasma quality)
Magnitude of increase correlates with degree of hepatocellular damage but not with reversibility of injury, prognosis or hepatic function
Short half lives: days in dogs, hours in cats (so even small increases may be significant in cats)
Which ‘cholestatic’ enzymes are there, used in small animals? What else can be used so assess if cholestasis?
ALP - good se for dogs but poor se for cats, scottish terriers have higher activities GGT - more specific Bilirubin Bile acids - more sensitive Cholesterol
What forms of ALP are there?
2 isoenzymes: intestinal and non tissue specific (I-ALP not generally detected in plasma as short half life so lost in GI tract)
Measurable isoforms:
- Liver-ALP (L-ALP) - serum half life of approx 70h in dog and 6h in cat (so insensitive in cats)
- Bone-ALP (B-ALP) - usually causes only mild increases, negative prognostic marker in osteosarcoma
- C-ALP - unique to dogs, induced by corticosteroids, product of I-ALP gene but produced in hepatocytes
What happens to senescent red cells to produce bilirubin?
Breakdown of haemorrhage to bilirubin in macrophages of reticula-endothelial system (tissue macrophages, spleen, liver)
Unconjugated bilirubin is transported in blood via albumin to the liver
Taken up by facilitated diffusion by liver and conjugated with glucoronic acid
Conjugated bilirubin actively secreted into bile then into intestine
In intestine glucorionic acid is removed by bacteria and bilirubin is converted to urobilinogen
Some of urobilinogen is reabsorbed from gut and enters portal blood
Some of this participates in the enterohepatic urobilinogen cycel
Remainder of urobilinogen is transported in blood to kidney, converted to yellow urobilin and excreted
Types of hyperbilirubinaemia?
Prehepatic - secondary to haemolytic, check for anaemia
Hepatic - can be due to decreased bilirubin uptake, conjugation and excretion (so hepatocyte dysfunction and intrahepatic cholestasis)
Post-hepatic - secondary to obstruction of extra hepatic bile duct, serum cholesterol often high, ultrasound useful
How is bilirubin measured?
Total bilirubin Conjugated bilirubin (=direct bilirubin) Unconjugated = Til-DirBil (=indirect bilirubin)
Clinical signs of hyperbilirubinaemia?
Jaundice persists long after liver function turned to normal due to delta-bilirubin bound to albumin
If jaundice is due to delta-bilirubin there will be no bilirubinuria
Liver functions?
Detoxification
Synthesis of cholesterol, bile acids, plasma proteins, clotting factors
Breakdown of RBCs
Metabolism of carbohydrates, lipids and amino acids
Removal of bacteria
Storage of glycogen, iron, copper, vitamins
What markers are there of decreased hepatocellular function?
Decreased uptake and excretion of bilirubin and bile acids - increased (unconjugated) bilirubin and bile acids
Decreased conversion of ammonia to urea - increased ammonia, decreased urea
Decreased synthesis of metabolites - decreased albumin, cholesterol coagulation factors and inhibitors, glucose (but hypoalbuminaemia, hypoglycaemia, hypocholesterolaemia are insensitive markers for decreased liver function)
Decreased synthesis of coagulation proteins - decreased fibrinogen, increased PT and PTT
Decreased immunologic function - decreased clearance of toxins and antigens -> systemic stimulation -> increased Igs
What markers are there of alteration of hepatic blood flow (PSS)?
Decreased uptake and excretion of bile acids - increased bile acids (bilirubin not usually increased as major problem is the bile acids re-uptake from blood)
Decreased conversion of ammonia to urea - increased ammonia
Decreased immunologic function - decreased clearance of toxins and antigens -> systemic stimulation -> increased Igs
Where is ammonia produced and what happens to it?
Produced in GIT by protein digestion or bacteria metabolism
Enters liver via portal vein
Uptaken by hepatocytes to synthesise urea, amino acids, proteins
Urea diffuses to sinusoidal blood or bile canaliculi and is excreted through kidneys or intestine
Things to note when measuring blood ammonia?
Relatively insensitive
Only significant if raised (hepatic encephalopathy)
Not stable in vitro so should be measured immediately after blood sampled
Elevated in:
- congenital and acquired porto-systemic shunts and liver failure
Where are bile salts produced and what happens to them?
Produced by hepatocytes
Released into biliary system and then intestine - allow fat absorption and digestion
>90% then reabsorbed from ileum, enter portal vein, return to liver, re-circulate
Small amounts lost in faeces, replaced by liver
What can increased bile acids in the blood mean?
Reduced uptake/excretion by hepatocytes - reduced hepatocellular mass, impaired hepatocyte function
Disruption of enterohepatic circulation - portosystemic shunts, cholestasis/bile obstruction
No point measuring BA if bilirubin already increased (BA more sensitive)
Interpretation of fasting SBA?
> 25-30mmol/L are abnormal and indicate hepatobiliary pathology - can’t differentiate between cholestasis and liver failure
<25-30mmol/L cannot completely exclude portosystemic shunt, perform bile acid stimulation test (BAST) if still suspecting hepatic pathology
Interpretation of post prandial SBA? How to do it?
BA stimulation test/dynamic BA Take resting sample Fatty meal Post-prandial sample 2h after feeding >25-30mmol/L is abnormal and indicates hepatobiliary pathology - can't differentiate between cholestasis and liver failure
What extra hepatic diseases can cause elevation in liver enzymes?
Hypoxia GI and pancreatic disease Endocrine diseases (fat or glycogen accumulation) Sepsis = 'reactive hepatopathies'
How to determine if raised liver enzymes is due to ‘reactive hepatopathy’ due to extra hepatic disease?
Most have normal bile acids
Other markers of liver function will be normal - unless affected by primary disease
Bile acids may be markedly elevated in sepsis/SIRS/endotoxaemic shock
What haematology may be seen in liver disease?
Microcytosis - portosystemic shunts or severe liver insufficiency, likely due to altered iron transport or metabolism
Ovalocytes (elliptocytes) are frequently seen in cats with hepatic lipidosis
Acanthocytes - lipid disorders, disruption of normal vasculature (e.g. hepatic haemangiosarcoma)
Urinalysis in liver disease?
Often unremarkable but may see:
- isosthenuria or inappropriately low USG
- bilirubinuria (more than 2+ in dogs, any in cats)
- ammonium bitrate crystals or uroliths (40-70% of patients with portosystemic shunts)
Functions of the pancreas?
Exocrine acinar cells (98%) - secrete enzymes involves in initial digestion of food
- proteases (trypsin, chymotrypsin, elastase)
- lipases
- amylases
- high conc of bicarbonate in secretions
- aids B12 and zinc absorption
- antibacterial activity
- intestinal mucosal modulation
- proteases stored as inactive zymogens
Endocrine islet cells (2%) - secrete insulin and glucagon
Tests for exocrine pancreas integrity?
Amylase and lipase tests - identify injury to pancreatic cells (increases most often due to pancreatitis), pancreatitis should be based on a combo of these tests with compatible clinical and imaging signs (abdominal ultrasound)
DGGR - proven to correlate well with more specific tests and clinical pancreatitis, cut offs for pancreatitis diagnosis:
- >34 U/L in cats
- >216 U/L in dogs
Canine pancreatic lipase (cPL) - considered more specific and more sensitive than lipase and amylase, snap test available
TLI (trypsin like immunoreactivity) - used in dogs, cats, horses (species specific assays), detects trypsinogen, trypsin and trypsin bound to protease inhibitors, use in animals with clinical signs of maldigestion/malabsorption, high se and sp for exocrine pancreatic insufficiency, less useful fro pancreatitis, serum TLI < 2.5mg/L in dogs, < 8mg/L in cats
Amylase - function, half life, species used in?
Catalyses hydrolysis of complex starches Short half-life (hours) Salivary and intestinal not found in serum More useful in dogs than other species Can increase due to decreased GFR
Lipase - function, half life etc?
Catalyses hydrolysis of triglycerides
Very short half-life (2 hours)
Mostly from pancreas
Can increase (mildly) due to decreased GFR
Different tests have different positive and negative predictive value
Diagnosis of pancreatitis?
Elevation in lipase (and amylase) - suggestive but other causes possible, higher increase=higher likelihood, degree of increase doesn’t = severity of disease
Need compatible clinical signs
Additional tests - PLI (specific pancreatic lipase), ultrasound, fluid analysis, biopsy
Suggested criteria for diagnosis of acute pancreatitis in dogs?
Absence of surgical disease on abdominal radiographs or analysis of abdominal fluid
And abdominal ultrasound with evidence of primary pancretitis
And one or more of the following:
- Spec-cPL >400ug/L
- Positive SNAP-cPL
- Gross lipaemia
- Serum PE-1 >17.24 ng/ml
- Total lipase >3x the upper reference interval
Indications for cytology?
Lesion (nodule, mass, plaque) palpable externally or seen on imaging Organomegaly Cavitary effusion Cancer staging PUO
Problems reducing cytology sample quality?
Ruptured cells - incorrect sampling or smearing technique
Inadequate staining
Identifying cell types on cytology?
Inflammatory cells - neutrophilic, eosinophilic, lymphocytic, histiocytic, mixed
Tissue cells - expected from organ aspirated, abnormal cells
Normal cytology of skin and subutaneous tissue?
Few keratinocytes
Scant fat
Rare sebocytes
How to assess neoplastic cells and malignancy from cytology?
Cell arrangement
- discrete or cohesive
- any cytoarchitecture
Cell shape
- round, polygonal, spindle
Criteria of malignancy
- hypercellularity (in mesenchymal tumours)
- pleomorphism (anisocytosis, anisokaryosis)
- high/variable N:C ratio
- multinucleation
- karyomegaly
- mitoses (especially if atypical)
- nuclear moulding (rapid cell growth)
- large, angular, or variably sized nucleoli
Minimum of 3 criteria to be classified as malignant (nuclear are stronger) - adapt depending on specific organ/cell type, allow some with inflammation and in histiocytes
If absent criteria of malignancy -> benign or well differentiated malignant
How do round cell tumours, epithelial tumours and mesenchymal tumours typically present on cytology?
Round cell tumour - ‘sea’ of round, discrete cells
Epithelial tumour - ‘islands’ of cohesive polygonal cells
Mesenchymal tumour - spindle cells with indistinct edges embedded in extracellular ‘matrix’
What round cell tumours are there?
Histiocytoma Plasma cell tumour Mast cell tumour Lymphoma Transmissible venereal tumour (not in UK)
Histiocytoma - Typical presentation? Cytology?
Dome shaped, alopecia, may be ulcerated
Tend to regress in a few weeks
Often (but not only) in young dogs
Cytology - light blue cytoplasm fading into the background, small lymphocytes often present and may predominate at later stages, sometimes difficult to differentiate from plasma cell tumour and lymphoma
Histiocytic sarcoma - cytology?
Arises from interstitial dendritic cells
Usually marked cell pleomorphism with karyomegaluy and multinucleation
Localised or disseminated
Lymphoma - cytology?
Round cells with high nucleus to cytoplasm ratio
Large blasts (larger than a neutrophil)
Monomorphic population
Mast cell tumour - cytology?
Magenta granules in the cytoplasm - sometimes don’t stain well with Diff Quik (send some unstained slides to lab)
Poor granulation can be due to poor differentiation (usually means a more aggressive tumour)
