Changes

==Introduction==

==Introduction==

[[File:Jaundiced cat.jpg|thumb|right|Image of a jaundiced cat, note the discoloured pinnae<br><small>(Image source Sabar 2007, Wikimedia Commons)</small>]]

Bilirubin is formed from the metabolism of heme groups in the liver, spleen and bone marrow and is taken up and conjugated by hepatocytes before excretion in the bile. Increased levels are associated with accelerated haemolysis, hepatobiliary disease and cholestatic disorders. Bilirubin is a fairly crude marker of hepatic function. Refrences: [[NationWide Laboratories]][[File:Jaundiced cat.jpg|thumb|right|Image of a jaundiced cat, note the discoloured pinnae<br><small>(Image source Sabar 2007, Wikimedia Commons)</small>]]

Bilirubin is a pigment formed from the haem groups of haemoglobin molecules. [[Erythrocytes|Red blood cells]] either undergo phagocytosis in the case of ageing cells or haemolysis in haemolytic crises. Haemoglobin is freed from the red cells and is further broken down in the reticulo-endothelial system to haeme and globulin. Haeme is a mixture of iron and porphyrin. The enzymatic conversion occurs within cells of the monocyte-phagocyte system (MPS) when haemoglobin is released by the degradation of red blood cells.

[[Erythrocytes|Red blood cells]] either undergo phagocytosis in the case of ageing cells or haemolysis in haemolytic crises. Haemoglobin is freed from the red cells and is further broken down in the reticulo-endothelial system to haeme and globulin. Haeme is a mixture of iron and porphyrin. The enzymatic conversion occurs within cells of the monocyte-phagocyte system (MPS) when haemoglobin is released by the degradation of red blood cells.

Both the iron and globulin are recycled for further use in [[erythropoiesis]]. The porphyrin from haemoglobin breakdown is converted to biliverdin, a green pigment, which may contribute to the greenish appearance seen in local bruising. Biliverdin is subsequently changed into bilirubin. This '''unconjugated''' bilirubin is not water soluble and is thus bound to albumin to be transported in the blood to the [[Liver - Anatomy & Physiology|liver]].

Both the iron and globulin are recycled for further use in [[erythropoiesis]]. The porphyrin from haemoglobin breakdown is converted to biliverdin, a green pigment, which may contribute to the greenish appearance seen in local bruising. Biliverdin is subsequently changed into bilirubin. This '''unconjugated''' bilirubin is not water soluble and is thus bound to albumin to be transported in the blood to the [[Liver - Anatomy & Physiology|liver]].

==Hyperbilirubinaemia==

==Hyperbilirubinaemia==

Bilirubin increases when the production of bilirubin exceeds the ability of the liver to recover unconjugated bilirubin from the bloodstream and process it, or when clearance of the conjugated form is altered by impaired hepatocyte processes or obstruction to the discharge of bilirubin into the intestines. Clinically, this means that hyperbilirubinaemia can be caused by heamolysis or choleostasis - the next step diagnostically is to establish if the inciting cause is [[Icterus#Causes_of_Icterus|prehepatic]], [[Icterus#Hepatic_Jaundice|hepatic]] or [[Icterus#Hepatic_Jaundice|posthepatic]].

Bilirubin increases when the production of bilirubin exceeds the ability of the liver to recover unconjugated bilirubin from the bloodstream and process it, or when clearance of the conjugated form is altered by impaired hepatocyte processes or obstruction to the discharge of bilirubin into the intestines. Clinically, this means that hyperbilirubinaemia can be caused by heamolysis or choleostasis - the next step diagnostically is to establish if the inciting cause is [[Icterus#Causes_of_Icterus|prehepatic]], [[Icterus#Hepatic_Jaundice|hepatic]] or [[Icterus#Hepatic_Jaundice|posthepatic]].

==Bilirubin in horses==

==Bilirubin in horses==

Horses have a different biliary excretion system to other animals and also readily develop jaundice in response to anorexia or intestinal disruption, so hyperbilirubinaemia can be difficult to interpret in the horse and elevated unconjugated bilirubin levels in the absence of any clinical signs might be of little consequence.

Horses have a different biliary excretion system to other animals and also readily develop jaundice in response to anorexia or intestinal disruption, so hyperbilirubinaemia can be difficult to interpret in the horse and elevated unconjugated bilirubin levels in the absence of any clinical signs might be of little consequence.

==Identification==

==Identification==

The '''Van de Berg test''' can be used to distinguish conjugated from unconjugated bilirubin. Plasma from an icteric animal is treated with an aqueous solution of the reagent '''diazotised sulphanilic acid''' and this produces a red-purple colour reaction. The intensity of this colour is directly proportional to the amount of water soluble (conjugated ) bilirubin in the sample. Further addition of alcohol intensifies the colour if there is non-water soluble (unconjugated) bilirubin also present. The intensified colour is directly proportional to the total amount of bilirubin present in the sample and the difference between the two readings gives the amount of unconjugated bilirubin in the sample.

The '''Van de Berg test''' can be used to distinguish conjugated from unconjugated bilirubin. Plasma from an icteric animal is treated with an aqueous solution of the reagent '''diazotised sulphanilic acid''' and this produces a red-purple colour reaction. The intensity of this colour is directly proportional to the amount of water soluble (conjugated ) bilirubin in the sample. Further addition of alcohol intensifies the colour if there is non-water soluble (unconjugated) bilirubin also present. The intensified colour is directly proportional to the total amount of bilirubin present in the sample and the difference between the two readings gives the amount of unconjugated bilirubin in the sample.

 

[[Category:Blood Biochemistry Changes]]

[[Category:Blood Biochemistry Changes]]