Liver Disease - Are Routine Diagnostic Tests of Value?

Icterus is the accumulation of yellow pigment in the blood and tissues. It is one of the most dramatic features of liver disease and is clinically recognised as jaundice. In healthy animals the red blood cells are normally removed from the circulation as they age. They are broken down into a number of components, one of which is bilirubin. This is processed in the liver and subsequently released from the liver into the intestines as one of the components of bile.

Hyperbilirubineamia is an increased concentration of bilirubin in the blood. It can occur for two reasons,

1.  An increased destruction of blood cells or

2.  Because the liver is unable to process the bilirubin

It is the accumulation of this pigment in the tissues that causes icterus or jaundice. 

What is normally involved in testing for liver disease?

All that is required initially is a small sample of blood obtained at around the same time as a urine sample. The blood sample will supply a complete blood count (CBC) and serum biochemistry analysis.

Complete Blood Count

CBC supplies the number and quality of the red blood cells, white blood cells and platelets. Red cell analysis will indicate any icterus present due to liver problems or breakdown of the red cells (haemolysis). The shape, size and appearance of the red blood cells is also analysed and this may give an indication regarding the presence of certain types of liver condition.

White cell count is also useful to indicate the presence of inflammation or infection. 

Serum Biochemistry

Serum biochemistry involves analysis of substances contained within the liquid portion of the blood. These include enzymes, fats, glucose and also metabolic waste products. Values for some of these constituents are often very helpful in assessing the presence of types of liver disease even if not supplying a definitive diagnosis of the liver problem. These enzymes include those found in liver cells, e.g. ALT (alanine aminotransferase) and AST (aspartate transaminase) although this enzyme is not entirely liver specific. However damage to the liver results in these enzymes circulating in the blood.

"Serum biochemistry involves analysis of substances contained within the liquid portion of the blood."

Other enzymes such as ALP (alkaline phosphotase) and GGT (gamma glutamyltransferase) are associated with cell membranes and can sometimes be useful in the unravelling of the liver problems. 

Bilirubin is an important biochemical test. Hyperbiliruibinaemia indicates an increased concentration of bilirubin in the blood. If haematology results indicate that this is not due to increased red blood cell destruction, it may be due to liver dysfunction.

Glucose, urea, cholesterol and albumin are among many substances made by the liver that are routinely measured in a serum biochemistry profile. A severe decrease in liver function can be reflected in a decrease in one or more of these substances.

Urine analysis

Kidneys constantly filter the blood to remove toxins and other waste, so occasionally we may see changes on urine analysis results before significant changes are noted with the blood indicative of liver disease. An example is an increase in the amount of bilirubin in the urine sample as is the presence of bilirubin crystals. This may point to an underlying liver disease which will later be shown on the blood analysis.

Is the serum biochemistry always abnormal when liver disease is present?

Sometimes liver disease is suspected on clinical signs but haematology and biochemistry may all be within normal limits.

Are other tests available then to help with the diagnosis?

There are several other tests which can be performed, probably the most important of which is a serum bile acid test. In addition, further testing may include ultrasound scans and liver biopsies as well as certain blood tests for specific infections. 

If you would like further information please do not hesitate to contact us. We will be happy to discuss additional or specialised tests which may be helpful.