Icterus

Jaundice (Icterus)

• this is a staining of the tissues with bilirubin or bilirubin complexes
• bile pigments have a strong affinity for elastic tissue and thus the yellowish colour can be easily seen in the sclera and mucous membranes in life and in the aorta at necropsy
• the serum bilirubion level gives an indication of the degree of icterus
  • dog's normal range is usually below 0.5mg/100ml
  • level is at least 2mg/100ml when jaundice is clinically evident

Causes

• overproduction of bilirubin
  • eg haemolytic crises
• diffuse liver disease
  • where there is a decreased uptake, conjugation, and secretion of bilirubin
• reduced outflow of bile into the gut
  • intrahepatic biliary obstruction eg foreign bodies, tumours, or fibrosis

Classification types

Haemolytic jaundice

• due to increased red cell destruction
  • results in increased amounts of bilirubin in the reticuloendothelial system
  • the production may be at a rate which exceeds the capacity of the liver to conjugate and eliminate it
• most of bilirubin is unconjugated
• bile pigment is not excreted in the urine
  • since the kidney can excrete only the water soluble conjugate
• diseases
  • Babesiosis
  • isoimmune reactions eg newborn foal whose dam has elaborated specific antibody against its red cells

Obstructive jaundice

• due to bile duct obstruction
• accumulation of conjugated bilirubin
• bile pigment is excreted in the urine
• bile pigment will be diminished in the faeces
• diseases
  • carcinoma involving the head of the pancreas

Hepatocellular jaundice

two factors are concerned in the production of jaundice following liver cell damage

• damage to liver cells can interfere with the passage of bile along the bile capillaries
  • eg intrahepatic obstruction
• Liver cell damage may cause failure of conjugation and therefore excretion failure of bile pigment