Cat & Dog - Jaundice Tests

What are the diagnostic tests?

Jaundice (icterus) is a condition characterised by an accumulation of bilirubin (a bile pigment) in the skin, mucous membranes and sclera (whites of the eyes) causing them to appear yellow in colour.

What are the causes?

There are three major causes of icterus:-

• red blood cell destruction (haemolysis)
• liver disease
• cholestasis (obstruction of the bile duct)

Normally blood cells are continually replaced.  Old red blood cells are broken down into several components, of which one is bilirubin.  This is processed by the liver, stored in the gall bladder and ultimately plays a part in the digestive process.

Increased bilirubin in the blood (hyperbilirubinaemia) occurs when increased destruction of red blood cells exceeds the liver's capacity to cope with the increased levels of bilirubin.  These levels then build up in the bloodstream. This also occurs if there is a problem processing bilirubin or releasing it by the liver or gall bladder.  As the circulating bilirubin increases, body tissues (such as the whites of the eyes, the lips and the skin) take on a yellow tinge.

How is jaundice accurately diagnosed?

The first step usually involves haematology, (i.e. complete blood count, CBC) and biochemistry.  The CBC will often identify abnormalities which help to indicate the cause of the red cell destruction.  For example, the presence of red blood cells with certain physical characteristics may indicate immune-mediated destruction of the red cells.

Biochemistry will indicate hyperbilirubinaemia (i.e. increased serum bilirubin) when the cause of the jaundice is increased red blood cell destruction.  Urine analysis will confirm the presence of hyperbilirubinaemia since the amounts of bilirubin in the urine will also have increased.  These tests will also give an indication if the cause of the problem is liver disease (hepatitis) or gall bladder disease (cholycystitis), either of which may result in an increased white blood cell count.

Serum biochemistry tests for certain liver enzymes, are good indicators of problems affecting the liver, gall bladder or bile duct.  Urine analysis (particularly serial samples) will often substantiate a tentative diagnosis. For example bile duct obstruction will be indicated by the absence of the urinary pigment (urobilinogen) in serial urine samples.

Are further tests necessary to establish the cause of the jaundice?

This will depend upon the individual case.  Testing can include ultrasound scans and on occasion fine needle biopsies.  If the cause is suspected as being infectious further specific tests may be carried out to isolate the infectious organism.  This applies particularly to cats where tests for Feline leukaemia, Feline infectious peritonitis or sometimes fungal diseases may have to be conducted.

Please contact us if you have any concerns.