Changes

==Causes of Icterus==

==Causes of Icterus==

===Prehepatic Jaundice===

===Pre-hepatic Jaundice===

This condition results from increased red blood cell destruction, overwhelming the capacity of the [[Liver - Anatomy & Physiology|liver]] to conjugate and excrete the bilirubin which is released into the plasma.  The majority of the bilirubin is therefore unconjugated and, unlike the conjugated form, this cannot be excreted by the [[Urinary System - Anatomy & Physiology|kidney]].  Possible causes of haemolysis and prehepatic jaundice include:

This condition results from increased red blood cell destruction, overwhelming the capacity of the [[Liver - Anatomy & Physiology|liver]] to conjugate and excrete the bilirubin which is released into the plasma.  The majority of the bilirubin is therefore unconjugated and, unlike the conjugated form, this cannot be excreted by the [[Urinary System - Anatomy & Physiology|kidney]].  Possible causes of haemolysis and prehepatic jaundice include:

*Haemolytic bacteria, including Clostridium haemolyticum in cattle and Leptospires in various species.

*'''Haemolytic bacteria''', including ''Clostridium haemolyticum'' in cattle and '''Leptospires''' in various species.

*Haemolytic parasites, including Babesiosis in cattle and dogs

*'''Haemolytic parasites''', including '''Babesiosis''' in cattle and dogs and ''Mycoplasma haemofelis'' in cats.

*Immune reactions to red blood cells, including:

*'''Immune reactions''' to red blood cells, including:

**Neonatal isoerthryolysis, resulting from the production of antibodies by the dam which are ingested by the neonate in colsotrum and subsequently cause destruction of red blood cells.  Bilirubin is able to cross the immature blood brain barrier and cause direct damage to the neurones of the brain, a phenomenon called '''kernicterus'''.

**'''Neonatal isoerthryolysis''', resulting from the production of antibodies by the dam which are ingested by the neonate in colsotrum and subsequently cause destruction of red blood cells.  Bilirubin is able to cross the immature blood brain barrier and cause direct damage to the neurones of the brain, a phenomenon called '''kernicterus'''.

**Autoimmune haemolytic anaemia or Immune-mediated haemolytic anaemia

**'''Autoimmune haemolytic anaemia''' or '''immune-mediated haemolytic anaemia'''.

**Destruction of red blood cells of lambs fed with colostrum from certain cattle

**Destruction of red blood cells of '''lambs fed with bovine colostrum'''.

*Hypophosphataemia, which may occur in Post-parturient Haemoglobinuria of cattle, rapid stabilisation of animals suffering from diabetic ketoacidosis with insulin and refeeding syndrome

*'''Hypophosphataemia''', which may occur in cattle with '''post-parturient haemoglobinuria''', in animals with '''diabetic ketoacidosis''' (DKA) which are rapidly stabilised with insulin and in '''refeeding syndrome'''.

*Inherited defects of red blood cell enzymes, including phosphofructokinase and pyruvate kinase

*'''Inherited defects of red blood cell enzymes''', including phosphofructokinase and pyruvate kinase.

*Microangiopathic damage to red blood cells as they pass through narrow or damaged blood vessels, as in haemangiosarcomata, disseminated intravascular coagulation (DIC) or vasculitis

*'''Microangiopathic damage''' to red blood cells as they pass through narrow or damaged blood vessels, as in '''haemangiosarcomata''', '''disseminated intravascular coagulation (DIC)''' or '''vasculitis'''.

*Oxidant damage to red blood cells, caused by paracetamol in cats, onion poisoning in dogs and copper toxicity in many species.  Ingestion of red maple leaves may also cause haemolysis in horses, as may brassicas (such as rape and kale) in cattle and sheep.

*'''Oxidant damage''' to red blood cells, caused by '''paracetamol''' in cats, '''onion poisoning''' in dogs and '''copper toxicity''' in many species.  Ingestion of red maple leaves may also cause haemolysis in horses, as may brassicas (such as rape and kale) in cattle and sheep.

Haemolysis which is sufficiently severe to cause icterus is likely to be life-threatening due to the reduction in oxygen-carrying capacity of the blood.  Animals affected acutely may require transfusions of whole blood, packed red blood cells or synthetic bovine haemoglobin and it may be advisable to provide oxygen by nasal catheter, flow-by or mask.  In addition, the presence of large amounts of haemoglobin may cause acute intrinsic renal failure (in addition to the pre-renal failure caused by the reduced oxygen delivery to the kidneys) and neonates may suffer from kernicterus, direct damage to the central nervous system by bilirubin.

Haemolysis which is sufficiently severe to cause icterus is likely to be life-threatening due to the reduction in oxygen-carrying capacity of the blood.  Animals affected acutely may require transfusions of whole blood, packed red blood cells or synthetic bovine haemoglobin and it may be advisable to provide oxygen by nasal catheter, flow-by or mask.  In addition, the presence of large amounts of haemoglobin may cause acute intrinsic renal failure (in addition to the pre-renal failure caused by reduced oxygen delivery to the kidneys) and neonates may suffer from kernicterus, direct damage to the central nervous system caused by bilirubin.

===Hepatic Jaundice===

===Hepatic Jaundice===

two factors are concerned in the production of jaundice following [[Liver - Anatomy & Physiology|liver]] cell damage

[[Liver - Anatomy & Physiology|Liver]] cell damage may lead to jaundice by two main mechanisms:

*damage to [[Liver - Anatomy & Physiology|liver]] cells can interfere with the passage of bile along the bile capillaries

*In '''acute hepatic necrosis''', bile flow is obstructed by the degree of swelling of damaged cells, obstructing the flow of bile in the canaliculi.

**eg intrahepatic obstruction

*[[Liver - Anatomy & Physiology|Liver]] cell damage may cause failure of conjugation and therefore excretion failure of bile pigment

 

This occurs due to an obstruction in the biliary tract which normally carriers bile from the liver and gall bladder to the duodenum.  Conjugated bilirubin is found in the urine but, in complete obstruction, urobilinogen will be absent from the urine and stercobilin from the faeces.  Possible causes of post-hepatic jaundice include:

*'''Intraluminal obstructions''':

**'''Choleliths''' ('gall stones') are much less common in animals than they are in humans.  They are usually composed of bilirubin salts in dogs and calcium carbonate in cats, although they are very rare in the latter species.

 

*due to bile duct obstruction

*due to bile duct obstruction

*accumulation of conjugated bilirubin

*accumulation of conjugated bilirubin