Approach to jaundice Flashcards
(29 cards)
How can we best define the CS of jaundice?
- hyperbilirubinaemia causing yellowing of body tissues
Fill in the blank: bilirubin is a product of … metabolism
- haemoglobin
Fill in the blank: most of haemoglobin metabolism occurs in the …
- liver
Fill in the blank: once conjugated in the liver, bilirubin enters the GIT at the …
- biliary tree - into the duodenum - enters at the duodenal papilla
Fill in the blank: urobilin is excreted in …
- urine
Fill in the blank: stercobilin is excreted in …
- faeces
Why is hyperbilirubinaemia problematic?
-> renal tubular damage
At what concentration of bilirubin in the blood is jaundice/icterus seen?
- hyperbilrubinaemia = >50µmol/l
Categories of jaundice
Pre-hepatic
- before the liver
- relates to increased haemoglobin destruction
Hepatic
- the liver doesn’t do its job
- reduced conjugation of bilirubin
Post-hepatic
- the conjugated bilirubin cannot exit via the biliary system
Cause of pre-hepatic jaundice
Oversupply of precursors (haemoglobin/haeme) into the system = increased destruction of RBCs.
Haemolytic anaemia
Causes of haemolytic anaemia
Acquired defects
- hypophosphataemia
- oxidative damage
– e.g. toxic insults (onion, garlic, paracetamol)
– metabolic dz e.g. hyperthyroidism, DM, renal dz
Genetic defects
- Abyssinian and somali cats: hereditary haemolysis
- non-spherocytic haemolytic anaemia in beagles
- phosphofructokinase deficiency in spaniels
Immune-mediated
- primary
- secondary
— drugs/toxins
— other immune dz e.g. systemic lupus erythematosus
— infectious e.g. FeLV, lepto, mycoplasma
— neoplasia e.g. lymphoma
Mechanical injury
- turbulent blood flow
— neoplasia e.g. haemangiosarcoma
— DIC
Internal haemorrhage
- look for other adverse effects
How do we tell if jaundice is pre-hepatic?
Haematology
- anaemia
— regenerative
— microcytic, hypochromic
- blood smear
— spherocytes
— auto-agglutination
Imaging
(primarily looking for neoplastic causes of IMHA)
- 3 view CXR, lung and abdo US
- advanced imaging: CT with contrast
Serum and urine discolouration
- haemoglobinaemia
- haemoglobinuria
– pink urine (haemoglobinuria) an indicator of intravascular haemolysis
Further bloods/infectious dz screening
Toxin/drug risk
Other clues e.g. pyrexia, pallor, haemic murmur
Causes of hepatic jaundice
Metabolism and delivery of heme into the system is normal.
The ability of the liver to process the bilirubin and excrete it is poor i.e. the liver is failing in some way, or the intrahepatic biliary tree is damaged/compressed by the liver around ot.
Infectious (hepatitis)
- bacterial
- fungal
- viral (CAV, FIV, FIP, FeLV)
Inflammatory
- cholangiohepatitis
Neoplasia
- lymphoma, MCT, adenocarcinoma
Drugs/toxins
- paracetamol, NSAIDs, etc
Degenerative
- amyloidosis
- lipidosis (cats)
- cirrhosis
Proximal biliary dz
- cholangitis/cholangiohepatitis
Liver enzymes
- ALT
- AST
- GGT
- ALP
ALT - what is it? when does it elevate?
- part of the pyruvate cycle
- inside liver cells
- serum elevations are consistent with hepatocellular damage
— dependent on numbers of liver cells present e.g. cirrhosis may be low/normal
— depends on number of cells damaged e.g. focal neoplasia vs widespread infection
AST - what is it? when does it elevate?
- found in liver and muscle (skeletal and cardiac)
- often elevated through venipuncture
- CK elevations often found concurrently if due to muscle damage
- resultantly many people disregard AST elevations on biochem
GGT - what is it? when does it elevate?
- part of glutathione metabolism and present in biliary tract cells (and pancreas, spleen, heart, brain)
- similar to ALP in terms of determining biliary tract dz and obstruction
- probably more useful in combination as can give false positives alone (esp cats)
ALP - what is it? when does it elevate?
- widespread in the body but is found in concentrated amounts in the biliary tree
- other: bone, gut, steroid induced
- even small elevations in cats could be significant due to a shorter T1/2 cf dogs (6h vs 66h)
- reactive hepatopathies: hyperadrenocorticism, DM, thyroid dz
- elevation often reflects biliary dz, but can still reflect liver changes
- animals with bigger skeletal turnover (young animals) will have increased ALP
Liver function tests - examples
- bile acid stimulation test (BAST)
- clotting factors
- albumin
- urea
- ammonia
Use/accuracy of liver function tests
Up to 70% of the liver may be lost before affects on function are seen, due to large functional reserve
Bile acid stimulation test (BAST) - what does it assess?
Will assess liver function and biliary flow -> bile acids are synthesised in the liver, secreted into the bile and moved in the duodenum. Reabsorbed from the GIT and return to the liver via the portal vein to be recycled and re-excreted into the gall bladder: entero-hepatic recycling
- this means these are an excellent test of liver function and/or biliary tract dz, but they are poor at differentiating between hepatic and post hepatic jaundice
Take a sample before and after eating
Clotting factors - use, which ones?
All produced by the liver (except VIII and vWF) -> prolonged aPTT and PT
Albumin - use
- produced by the liver
- low values may support liver dz (<15g/l -> oedema/ascites)
Urea - use
- urea is an end product of protein metabolism and ammonia production
- low values support reduced liver function
