Diagnosing Jaundice

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.

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 one of which 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. This then circulates in the bloodstream. This can also occur if there is a problem processing the bilirubin or releasing it by the liver or gall bladder. If this starts to accumulate then tissues and the whites of the eyes or the lips take on a yellow tinge.

How is it 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 point to the cause of the red cell destruction. For example the presence of red blood cells with certain physical characteristics may support a diagnosis of immune mediated destruction of red cells or they may seem to be more fragile. Alternatively the jaundice may be due to red cell destruction (haemolysis).

Biochemistry will confirm the jaundice by indicating hyperbilirubinaemia, i.e. increased serum bilirubin. When the cause of the jaundice is increased red blood cell destruction, this hyperbilirubinaemia will occur with anaemia. Urine analysis would confirm the presence of hyperbilirubinaemia since the amounts of bilirubin in the urine will also have increased. Similarly these tests will also give an indication if the cause of the problem is liver disease or gall bladder disease, e.g. an increased white blood cell count may be noted in the case of inflammation of either the liver (hepatitis) or the gall bladder (cholecystitis).

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, e.g. bile duct obstruction simply by the absence of the urinary pigment, urobilinogen in serial samples.

Are further tests necessary to establish a definite diagnosis of jaundice?

This will depend upon the individual patient but testing can include ultrasound scans and, on occasion, fine needle biopsies, the samples from which will be subjected to various tests. If the cause is suspected as being infectious, further specific tests may be carried out. This applies particularly in the case of cats where tests for feline leukaemia, feline infectious peritonitis or sometimes fungal diseases may have to be conducted.